J. Inher. Metab. Dis. 15 (1992) 188-197 © SSIEMand KluwerAcademicPublishers.Printedin the Netherlands
Persistent Hypermethioninaemia with Dominant Inheritance H. J. BLOM1'2., A. J. DAVtDSON3, J. D. FINKELSTEIN4, A. S. LUDER3, I. BERNARDINI1, J. J. MARTIN't, A. TANGERMAN5, J. M. F. TRIJBELS2, S. H. MUDD6, S. L GOODMAN3 and W. A. GAHL 1 1Section on Human Biochemical Genetics, Human Genetics Branch, National Institute of Child Health and Human Development, Bethesda, MD 20892, USA; 2Department of Pediatrics, University Hospital, Nijmegen, The Netherlands; 3Department of Pediatrics, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Denver, CO 80262, USA; 4Department of Veteran Affairs Medical Center, Washington, DC 20422, USA; 5Division of Gastrointestinal and Liver Diseases, Department of Medicine, University Hospital Nijmegen, The Netherlands; 6National Institute of Mental Health, Bethesda, MD 20892, USA Summary: A clinically benign form of persistent hypermethioninaemia with probable dominant inheritance was demonstrated in three generations of one family. Plasma methionine concentrations were between 87 and 475 pmol/L (normal mean 26/~mol/L; range 10-40 #mol/L); urinary methionine and homocystine concentrations were normal. Plasma homocystine, cystathionine, cystine and tyrosine were virtually normal. The concentrations in serum and urine of metabolites formed by the methionine transamination pathway were normal or moderately elevated. Methionine loading of two affected family members revealed a diminished ability to catabolize methionine, but the activities of methionine adenosyltransferase and cystathionine fl-synthase were not decreased in fibroblasts from four affected family members. Fibroblast methylenetetrahydrofolate reductase activity and its inhibition by S-adenosylmethioninewere also normal, indicating normal regulation of NS-methyltetrahydrofolate-dependent homocysteine remethylation. Serum folate concentrations were not increased. The findings in this family differ from those previously described for known defects of methionine degradation. Since the hepatic and fibroblast isoenzymes of methionine adenosyltransferase differ in their genetic control, this family's biochemical findings appear consistent with a mutation in the structural gene for the hepatic methionine adenosyltransferase isoenzyme. The known inborn errors of methionine catabolism include deficiencies of cystathionine fl-synthase (CS) (EC 4.2.1.22) (McKusick 23620), y-cystathionase (EC 4.4.1.1) Correspondence: Dr H. J. Blom, Department of Pediatrics, University Hospital Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands MS received 23.5.91 Accepted 25.11.91 188
Dominant Hypermethioninaemia
189
(McKusick 21950) and hepatic methionine adenosyltransferase (MAT) (EC 2.5.1.6) (McKusick 25085). All these defects involve the transsulphuration pathway (Figure 1). Hepatic MAT deficiency, considered a benign disorder (Gahl et al 1988; Mudd et al 1989; Finkelstein 1990), results in elevated plasma and urine methionine levels, yCystathionase deficiency, also apparently benign, is characterized by increased cystathionine concentrations, with normal levels of other transsulphuration metabolites. CS deficiency is associated with premature atherosclerosis, thromboembolism, ectopia lentis, osteoporosis and mental retardation (Boers et al 1983; Mudd et al 1985; Ueland and Refsum 1989). Both methionine and homocysteine levels are usually increased in CS-deficient patients. Hypermethioninaemia can originate also from liver disease, tyrosinaemia type I (McKusick 276700), or the ingestion of D-methionine or 6-azauridine. It can occur transiently in young children on high-protein diets, or be persistent with normal hepatic MAT, with or without myopathy, in association with high folate levels (Mudd et al 1989). A single patient with persistent hypermethioninaemia, normal hepatic MAT and normal folate levels has been reported with developmental delay and failure to thrive (Jhaveri et al 1982). Recently, a pedigree was described with hypermethioninaemia, decreased hepatic adenosylhomocysteine hydrolase (EC 3.3.1.1) activity and severe clinical manifestations, including failure to thrive, mental and motor retardation, facial dysmorphisms, and cardiomyopathy (Labrune et al 1990). All three defined defects of methionine catabolism are considered to be inherited as autosomal recessive traits. In the present report, we describe our investigation of a new form of persistent hypermethioninaemia inherited in a dominant fashion in three generations of one family.
I TRANSAMINATION 1 i PATHWAY I
TRANSSULFURATIONPATHWAY
J
iI '7
l
8
,3 i
1
i / CYSTEINE SULFATE
tranamlthylltlon
S-ADENOSYL- = HOMOCYSTE,NE
2
l9 3-METHYLTHIOPROPIONATE
[
[
~ S-ADENOSYLMETHIONINE
METHANETHIOL ! SULFATE o...o.o,ox,oE
DIMETHYLSULFIDE
Figure 1 Methionine metabolism: (1) methionine adenosyltransferase; (2) methyltransferase; (3) S-adenosylhomocysteine hydrolase; (4) betaine-homocysteine methyltransferase; (5) 5methyltetrahydrofolate-homocysteine methyltransferase; (6) cystathionine fl-synthase; (7) 7cystathionase; (8) transaminase; (9) branched-chain 2-oxoacid dehydrogenase J. Inher. Metab. Dis.
15 (1992)
190
Blom et al.
METHODS
Amino acids were quantitated using an LKB 4150 alpha plus amino acid analyser (LKB Biochrom, Ltd., Cambridge, UK). Heparinized plasma was deproteinized with 5% sulphosalicylic acid within 30min of collection, filtered through 0.22 #m Millipore membranes (Millipore Corp., Bedford, MA, USA), and stored at - 2 0 ° C prior to analysis. Urine samples were collected over 24 hours and also stored at - 2 0 ° C prior to analysis. Amino acids:
Methionine loading: After an overnight fast, an oral dose of 0.1 g L-methionine/kg body weight was administered to the two sisters, II-1 and II-2. Details of the loading procedure and control values in 23 healthy volunteers have been previously described (Blom et al i989a). Transamination metabolites: The transamination metabolites measured in urine and non-deproteinized serum consisted of 4-methylthio-2-oxobutyrate and methanethiol mixed sulphides. The assays in serum have been described previously (Blom et al 1989b). The sum of the concentrations of these metabolites represents a relative measure of the amount of methionine degraded via the transamination pathway (Gahl et al 1988; Blom et al 1989b).
Normal fibroblasts (GM 3651, GM 5659, GM 3440, GM 5757, GM 1501, GM 1489, GM 5758) were obtained from the Human Mutant Cell Repository (Camden, NJ, USA). As described previously (Blom et al 1990), fibroblasts were grown to confluence in Eagle's minimum essential medium containing 10% fetal bovine serum (Gibco, Grand Island, NY, USA), and harvested by trypsinization. Ceil culture:
Enzymes: Fibroblasts were washed three times and suspended in 0.1 mol/L KH2PO 4 (pH 7.4), sonicated, and centrifuged at 2500 g for 10 min. MAT and CS were assayed as described by Mudd et al (1965), with some modifications (Gahl et al 1987). Methylenetetrahydrofolate reductase (MTHFR, EC 1.1.99.15) was assayed according to Finkelstein et al (1978). Protein was measured by the Bio-Rad protein assay.
FAMILY REPORT
Two caucasian male first cousins (III-1, III-2) were ascertained by the presence of hypermethioninaemia on neonatal screening for CS deficiency. Because their hypermethioninaemia persisted during the first year of life, fluctuating between 87 and 475 #mol/L (Table 1), they and other family members were further investigated. Figure 2 gives the family pedigree. The probands' mothers (II-1 age 31, and II-2 age 30) were sisters and they and their father (I-1 age 53) also exhibited hypermethioninaemia (Table 2). The sisters' mother (I-2), one brother (II-4), and the husband (II-3) of II-2 were tested for hypermethioninaemia and found to be normal. Another brother (II-5) died of astrosarcoma at age 25 years. Urinary excretion of methionine was normal in all family members tested (Table 2). Recently, II-2 gave birth to a second body (III-3), who was also positive for hypermethioninaemia on neonatal screening. J. Inher. Metab. Dis. 15 (1992)
191
Dominant Hypermethioninaemia
Table 1 Plasma methionine concentrations of III-1 and III-2 in their first 2 years of life Age
(months) 0 1 2 3 4 7 8 9 10 20
Plasma methionine (#mol/L) III-1
111-2
475 474 277 209 87 152 161
176 389 358 138 t98 173 221
I
II
Ill Figure 2 Pedigree of the hypermethioninaemic family, showing a pattern of dominant inheritance. II-5 died of astrosarcoma
On physical examination, both the mothers (II-1 and II-2) and their children (III1 and iII-2), who were seen on several occasions during their first year of life, were normal, with no hepatomegaly. All ate normal diets with normal protein intakes. There was no history of liver disease, hepatitis, transfusions, exposure to hepatotoxins, or manifestations suggestive of thromboembolic events. They were receiving no medications, in particular no 6-azauridine. There was no history of consanguinity. The children's birth, growth, and development were entirely normal. None of the affected family members showed the fetor due to increased dimethylsulphide expiration associated with extensive methionine degradation via the transamination pathway (Gout et al 1975; Gaht et al 1988; Blom et al 1989b). Homocytine, cystathionine, cystine and tyrosine concentrations were normal in plasma and urine of the probands and their mothers and in the plasma of III-3 and of I-1. Routine liver function tests including alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase and gammaglutamyltranspeptidase were normal for H I - I , II-1, III-2 and II-2.
d. Inher. Metab. Dis. 15 (1992)
192
Biota et al.
Table 2 Plasma and urine methionine in family members (Fig. 2) Methionine
III- 1 111-2 III-3 II-i II-2 II-4 1I-5 1-2 I- 1 Normal children Mean (n = 10) Range Normal adults Mean (n = 16) Range
Plasma
Urine
(/~mol/L)
(/zmol/24 h)
See Table 1 See Table 1 156 137, 77 104, 73 42 34 55 203
51 50 142 141 -
26 10-40
46 16-130
26 10-42
63 22-225
RESULTS AND DISCUSSION The cause of hypermethioninaemia in this kindred was investigated systematically. Generalized liver disease was ruled out by the normal liver function tests and normal tyrosine levels. No family member manifested hyperhomocystinaemia or any clinical symptoms of homocystinuria due to CS deficiency. Fibroblast CS activities of II-1 (9.2 nmol (rag protein)- i (135 rain)- 1) and II-2 (14.3 nmol (rag protein)- i (135 rain)- 1) were within the range of the four concurrently assayed normals (6.3, 6.6, 6.8 and 22.3 nmol (rag protein) -1 (135 rain)-1) and the CS activities of the probands III-I (56.7nmol (rag protein) -I (135rain) -1) and III-2 (31.1nmol (rag protein) -1 (135 rain)-1) were actually higher than the normal levels. These results prompted investigation of methionine catabolism, which occurs by either transamination or adenosylation and subsequent transsulphuration (Figure 1). Transsulphuration predominates in humans, although up to 20% of methionine degradation may occur via the transamination pathway in the presence of hepatic MAT deficiency (Gahl et al 1988; Blom et al 1989b). The ability of the two affected sisters to catabolize methionine was tested by loading them with 0.1 g L-methionine/kg body weight. In normal control subjects this produces a rapid increase in plasma methionine followed by a gradual decrease (Figure 3). In the two sisters (II-1 and II-2) plasma methionine concentrations rose more rapidly, but decreased very slowly, and remained more than three standard deviations above the normal mean 8 hours after loading (Figure 3). This resembled methionine loading tests for homozygote CS-deficient patients (Blom et al 198%). The transamination pathway was investigated by measuring the sum of two of its metabolites, 4-methylthio-2-oxobutyrate and methanethiol mixed disulphides (Gahl J. Inher. Metab. Dis. 15 (1992)
Dominant Hypermethioninaemia 2000
193
Plasma Methionine C o n c e n t r a t i o n
1000
/ ,'/I ~ T
-o
/,'N 0 0
(/zmol/I)
T
I
I
4
8
T i m e (h) Figure 3 Plasma methionine concentrations before (Oh) and after (1-8 h) oral L-methionine loading in 23 normals (+) and the two hypermethioninaemic women II-1 (O) and II-2 (O). Bars give SD of the mean et al 1988; Blom et al 1989b), in serum and urine. After an overnight fast, the serum levels for III-1, II-1, III-2 and II-2 (0.53, 0.48, 0.68 and 0.81 #mol/L) were within the normal range (0.32-1.20#mol/L, n--23). Urine levels were also normal in II-1 (1.1mmol/mol creatinine) and II-2 (2.2mmol/mol creatinine), and only slightly elevated in III-1 (3.9 mmol/mol creatinine) and III-2 (3.0mmol/mol creatinine). (The normal range is 0.7-2.1 mmol/mol creatinine, n = 23.) After a methionine load, the serum concentrations of the transamination metabolites remained normal for II-2 but for II-1 were more than three standard deviations above the normal mean 2-8 hours after loading (Figure 4). These findings confirm that the methionine transamination pathway was intact; any elevations probably reflect increased concentrations of the substrate, methionine. MAT deficiency could explain this family's hypermethioninaemia, although the patients' plasma methionine concentrations were lower than usually reported in MAT deficiency (Gout et al 1975; Finkelstein et al 1975; Gaull et al 1981a; Gahl et al 1988; Mudd et al 1989). Fibroblast MAT activities were normal in III-1 (2.8nmol (mg protein)- 1 (120 min)- 1) and II-1 (2.9 nmol (mg protein)- 1 (120 min)- 1 and slightly decreased in III-2 (1.Snmol (mg protein) -1 (120min) -1) and II-2 (2.2nmol (mg protein)-: (120min) -1. The values of four concurrently assayed normals were 2.5, 2.9, 3.6 and 3.8 nmol (mg protein)-1 (120 min)-1. The fibroblast isoenzyme of MAT differs in its genetic control from the hepatic isoenzymes which handle the bulk of the body's methionine adenosylation (Gahl et al 1988; Mudd et al 1989; Finkelstein 1990), so a partial hepatic MAT deficiency remains possible. The normal or only moderately elevated concentrations of transamination metabolites in our family compared with one MAT-deficient patient (Gahl et al 1988) correlated with the low degree of hypermethioninaemia. A liver biopsy, which does not appear medically J. lnher. Metab. Dis. 15 (1992)
Blom et al.
194
26
Transamination M e t a b o l i t e s (/~mol/I)
/,O/
~" ~'~ ~ , . . ~
/ 13
/
/
/
----i- . . . . . . 0
z~
8
T i m e (h) Figure 4 Serum transamination pathway metabolites before (Oh) and after (1-8h) oral L-methionine loading in 10 normal women (+) and the two hypermethioninaemicwomen II1 (O) and II-2 (O). Bars gives SD of the mean. (Normal men were excluded because of the observed difference in methionine catabolism via the transamination pathway between premenopausal women and young men after methionine loading. (Blom et al 1988)) indicated, could assess hepatic MAT activity as well as the concentration of Sadenosylmethionine, which, if decreased in the face of hypermethioninaemia, would virtually assure the presence of a functional MAT deficiency. Excessive remethylation of homocysteine, using either NLmethyltetrahydrofolate or betaine as methyl donor, offered an alternative explanation for the hypermethioninaemia in this family. The formation of NLmethyltetrahydrofolate by methylenetetrahydrofolate reductase (MTHFR) is inhibited by S-adenosylmethionine (Kutzbach and Stokstad 1967; Jencks and Matthews 1987), and the betaine-dependent methylation of homocysteine is inhibited by methionine (Finkelstein et al 1972; Finkelstein and Martin 1986). A failure of either of these regulatory inhibitions might lead to a higher steady-state level of methionine, despite a normal transsulphuration. Mean fibroblast MTHFR activities (_+_SD) of four affected family members (II-t, II-2, III-1 and III-2) were 4.2 4- 1.4 nmol (mg protein)- 1 h- 1 (range 3.0-5.8), compared with 6.5 + 2.0nmol (mg protein)-1 h-1 (range 4.4-8.3) for the four normal subjects. In the presence of 0.2 mmol/L S-adenosylmethionine, the mean activity of MTHFR (_ SD) of the family members was 64 + 12% of the uninhibited value; for controls it was 71 _+ 9% of the uninhibited value. This normal S-adenosylmethionine inhibition of MTHFR runs counter to the hypothesis that excess homocysteine remethylation occurred due to unregulated synthesis of 5-methyltetrahydrofolate.Betaine-homocysteine methyltransferase present in human liver (Ericson 1960; Finkelstein 1990) and kidney (Mudd et al 1970a; McKeever et al 1991) is not measurable in cultured human fibroblasts (Mudd et al 1970b). Therefore, its regulation could not be tested. J. lnher. Metab. Dis. 15 (1992)
Dominant Hypermethioninaemia
195
Four patients with hypermethioninaemia, apparently normal hepatic MAT activity, and increased folate concentrations have been reported. Ten-fold elevated serum folate concentrations were noted in three clinically normal hypermethioninaemic neonates by Tsuchiyama et al (1982), and elevated serum fotate concentrations were reported in a girl with persistent hypermethioninaemia accompanied by myopathy and poor mental development (Gaull et al 1981b). However, the serum folate levels of our patients III-1 and III-2 were 7.6ng/ml and 33.1 ng/ml, respectively (normal < 30 ng/ml), ruling out this type of hypermethioninaemia in the present family. We are left with a kindred in which benign hypermethioninaemia appears to be dominantly inherited. One possible explanation is that the affected family members are heterozygous for a mutation in the structural gene for hepatic MAT, which produces a deviant gene dosage effect upon the catalytic activity such that the heterozygote form has less than 50% of the normal activity but more than in previously described patients with severe deficiencies of hepatic MAT. Such a mutation would be consistent also with the moderately increased concentrations of transamination pathway metabolites in urine of III-1 and III-2, and in serum of II2 after methionine loading (Figure 4). Liver MAT exists in two forms, a dimer (~z) and a tetramer (~4) of the same subunit (Cabrero et al 1987). Negative functional interactions between mutant and normal subunits therefore provide one mechanism for the postulated deviant gene dosage effect. Cabrero et al (1988) reported that in human hepatic cirrhosis there is a specific loss of the tetramer as compared to the dimer, as well as a decrease in overall hepatic MAT activity and suggested that this decrease may explain the hypermethioninaemia of cirrhosis. The possibilities exist that a mutation in the structural gene for MAT, or in that for a currently hypothetical MAT-processing enzyme, might lead to a failure of conversion of the dimeric form of hepatic MAT to the tetrameric form. Further investigations into these possibilities and their functional implications await the availability of appropriate tissues for study. ACKNOWLEDGEMENT This project was supported in part by grant no. MCJ000252, US Department of Health & Human Services, Public Health Service, Bureau of Maternal and Child Health and Resources Development, a grant (RR-69) from the General Clinical Research Center Program, National Institutes of Health, Rockville, MD, USA and The Netherlands Heart Foundation. Dr Finkelstein is supported by grant DK-13048 from the National Institutes of Health and by the Medical Research Service, Department of Veterans Affairs. REFERENCES Blom HJ, Boers GJH, van den Elzen PAM, van Roessel JJM, Trijbels JMF, Tangerman A (1988) Differences between premenopausal women and young men in the transamination pathway of methionine catabolism, and the protection against vascular disease. Eur J Clin Invest 18:633-639 Blom HJ, Boers GHJ, Trijbets JMF, van Roessel JJM, Tangerman A (t989a) Cystathionine synthase deficient patients do not utilize the transamination pathway of methionine to reduce hypermethioninemiaand homocystinemia.Metabolism 38:577-582 J. Inher. Metab. Dis. 15 (1992)
196
Blom et al.
Blom H J, Boers GHJ, van den Elzen PAM, Gahl WA, Tangerman A (1989b) Transamination of methionine in humans. Clin Sei 76:43-49 Blom HJ, Andersson HC, Seppala R, Tietze F, Gahl WA (1990) Defective glucuronic acid transport from lysosomes of infantile free sialic acid storage disease fibroblasts. Biochem J 268:621-625 Boers GHJ, Smals AGH, Drayer JIM, Trijbets JMF, Leermakers AI, Kloppenborg PW (1983) Pyridoxine treatment does not prevent homocystinemia after methionine loading in adult homocystinuria patients. Metabolism 32:390-397 Cabrero C, Puerta J, Alemany S (1987) Purification and comparison of two forms of Sadenosyl-L-methionine synthetase from rat liver. Eur J Biochem 170:299-304 Cabrero C, Duce AM, Ortiz P, Alemany S, Mato JM (1988) Specific loss of the high-molecular weight form of S-adenosyl-S-methionine synthase in human liver cirrhosis. Hepatology 8: t530-1534 Ericson LE (1960) Betaine-homocysteine-methyl-transferases. I. Distribution in nature. Acta Chem Scand 14:2102-2112 Finkelstein JD (1990) Methionine metabolism in mammals. J Nutr Biochem 1:228-237 Finketstein JD, Martin JJ (1986) Methionine metabolism in mammals. Adaptation to methionine excess. J Biol Chem 261:1582-1587 Finkelstein JD, Harris BJ, Kyle WE (1972) Methionine metabolism in mammals: Kinetic study of betaine-homocysteine methyltransferase. Arch Biochem Biophys 153:320-324 Finkelstein JD, Kyle WE, Martin JJ (1975) Abnormal methionine adenosyltransferase in hypermethioninemia. Biochem Biophys Res Commun 66:149t-1497 Finkelstein JD, Martin JJ, Kyle WE, Harris BJ (1978) Methionine metabolism in mammals: Regulation of methylenetetrahydrofolate reductase content of rat tissues. Arch Biochem Biophys 181:153-160 Gahl WA, Finkelstein JD, Mullen KD et al (1987) Hepatic methionine adenosyltransferase deficiency in a 31-year-old man. Am J Hum Genet 40:39-49 Gahl WA, Bernardini I, Finkelstein JD et al (1988) Transsulfuration in an adult with hepatic methionine adenosyltransferase deficiency. J Ctin Invest 81:390-397 Gaull GE, Tallan HH, Lonsdale D, Przyrembel H, Schaffner F, von Bassewitz DB (1981a) Hypermethioninemia associated with methionine adenosyltransferase deficiency: clinical, morphologic, and biochemical observations on four patients. J Pediatr 98:734-741 Gaull GE, Bender AN, Vulovic D, Tallan HH, Schaffner F (1981b) Methioninemia and myopathy: a new disorder. Ann Neurol 9:423-432 Gout JP, Serre JC, Dieterlen M e t al (1975) Une nouvelle cause d'hypermethioninemie de l'enfant. Arch Franc Ped 34:416-423 Jencks DA, Matthews RG (1987) Allosteric inhibition of methylenetetrahydrofolate reductase by adenosylmethionine. J Biol Chem 262:2485-2493 Jhaveri BM, Buist NRM, Gaull GE, Tallan HH (1982) Intermittent hypermethioninemia associated with normal hepatic methionine adenosyltransferase activity: report of a case. J Inher Metab Dis 5:101-105 Kutzbach C, Stokstad ELR (1967) Feedback inhibition of methylene-tetrahydrofolate reductase in rat liver by S-adenosylmethionine. Biochim Biophys Acta 139:217220 Labrune P, Perignon JL, Rault M et al (1990) Familial hypermethioninemia partially responsive to dietary restriction. J Pediatr 117:220-226 McKeever MP, Weir DG, Molloy A, Scott JM (1991) Betaine-homocysteine methyltransferase: organ distribution in man, pig and rat and subcellular distribution in the rat. Clin Sci 81: 551-556 Mudd SH, Finkelstein JD, Irreverre F, Laster L (1965) Transsulfuration in mammals. Microassays and tissue distributions of three enzymes of pathway. J Biol Chem 240: 43824392 Mudd SH, Levy HL, Morrow G I I I (1970a) Deranged B~2 metabolism: Effects on sulfur amino acid metabolism. Biochem Med 4:193-214
J. tnher. Metab. Dis. 15 (1992)
Dominant Hypermethioninaemia
197
Mudd SH, Uhlendorf BW, Hinds KR (1970b) Deranged B12 metabolism: studies of fibroblasts grown in tissue culture. Biochem Med 4:215-239 Mudd SH, Skovby F, Levy HL et al (1985) The natural history of homocytinuria due to cystathionine fl-synthase deficiency. Am J Hum. Genet 37:1-31 Madd SH, Levy HL, Skovby F (1989) Disorders of transsulfuration. In Scriver LR, Beaudet AL, Sly WS, Valle D eds. The Metabolic Basis of Inherited Disease, 6th edn. New York: McGraw-Hill, 693-734 Tsuchiyama A Oyanagi K, Nakata F et al (1982) A new type of hypermethioninemia in neonates. Tohoko J Exp Med 138:281-288 Ueland PM, Refsum H (1989) Plasma homocysteine, a risk factor for vascular disease: plasma levels in health, disease, and drug therapy. J Lab Clin Med 114:473-501
J. Inher. Metab. Dis. 15 (1992) 197
© SSIEM and Ktuwer AcademicPublishers. Printed in the Netherlands BOOK
REVIEW
Peroxisomes
- a p e r s o n a l account. Frank Roels. VUB Press, Brussels, 1991, about
£13 This monograph by Professor Frank Roels describes his experiences with peroxisomes over a period of more than 20 years. The content is a personal view, but since he has been involved with peroxisomes as morphological curiosities, as markers of Zellweger syndrome by their absence, and in more recent years as indicators of peroxisomal dysfunction by their abnormal dimensions or shapes, it is a very valuable and readable text. The author draws together morphological, histochemical and biochemical evidence and relates this to function in the normal and in peroxisomal disorders, and to the biogenesis of peroxisomes. Some of the views expressed might be considered controversial but there are few people who have had such extensive peroxisomal experience, and the arguments should be taken seriously. This text, and the extensive reference list (around 400 references are cited) complements the recent article in the Journal (1991; 14: 853-857). It should be read by all who have even a passing interest in peroxisomes and metabolic disorders. The one question to which I failed to find the answer is "What happened when he kissed the toad?" B. D. Lake
J. Inher. Metab. Dis. 15 (1992)
Persistent Hypermethioninaemia with Dominant Inheritance H. J. BLOM1'2., A. J. DAVtDSON3, J. D. FINKELSTEIN4, A. S. LUDER3, I. BERNARDINI1, J. J. MARTIN't, A. TANGERMAN5, J. M. F. TRIJBELS2, S. H. MUDD6, S. L GOODMAN3 and W. A. GAHL 1 1Section on Human Biochemical Genetics, Human Genetics Branch, National Institute of Child Health and Human Development, Bethesda, MD 20892, USA; 2Department of Pediatrics, University Hospital, Nijmegen, The Netherlands; 3Department of Pediatrics, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Denver, CO 80262, USA; 4Department of Veteran Affairs Medical Center, Washington, DC 20422, USA; 5Division of Gastrointestinal and Liver Diseases, Department of Medicine, University Hospital Nijmegen, The Netherlands; 6National Institute of Mental Health, Bethesda, MD 20892, USA Summary: A clinically benign form of persistent hypermethioninaemia with probable dominant inheritance was demonstrated in three generations of one family. Plasma methionine concentrations were between 87 and 475 pmol/L (normal mean 26/~mol/L; range 10-40 #mol/L); urinary methionine and homocystine concentrations were normal. Plasma homocystine, cystathionine, cystine and tyrosine were virtually normal. The concentrations in serum and urine of metabolites formed by the methionine transamination pathway were normal or moderately elevated. Methionine loading of two affected family members revealed a diminished ability to catabolize methionine, but the activities of methionine adenosyltransferase and cystathionine fl-synthase were not decreased in fibroblasts from four affected family members. Fibroblast methylenetetrahydrofolate reductase activity and its inhibition by S-adenosylmethioninewere also normal, indicating normal regulation of NS-methyltetrahydrofolate-dependent homocysteine remethylation. Serum folate concentrations were not increased. The findings in this family differ from those previously described for known defects of methionine degradation. Since the hepatic and fibroblast isoenzymes of methionine adenosyltransferase differ in their genetic control, this family's biochemical findings appear consistent with a mutation in the structural gene for the hepatic methionine adenosyltransferase isoenzyme. The known inborn errors of methionine catabolism include deficiencies of cystathionine fl-synthase (CS) (EC 4.2.1.22) (McKusick 23620), y-cystathionase (EC 4.4.1.1) Correspondence: Dr H. J. Blom, Department of Pediatrics, University Hospital Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands MS received 23.5.91 Accepted 25.11.91 188
Dominant Hypermethioninaemia
189
(McKusick 21950) and hepatic methionine adenosyltransferase (MAT) (EC 2.5.1.6) (McKusick 25085). All these defects involve the transsulphuration pathway (Figure 1). Hepatic MAT deficiency, considered a benign disorder (Gahl et al 1988; Mudd et al 1989; Finkelstein 1990), results in elevated plasma and urine methionine levels, yCystathionase deficiency, also apparently benign, is characterized by increased cystathionine concentrations, with normal levels of other transsulphuration metabolites. CS deficiency is associated with premature atherosclerosis, thromboembolism, ectopia lentis, osteoporosis and mental retardation (Boers et al 1983; Mudd et al 1985; Ueland and Refsum 1989). Both methionine and homocysteine levels are usually increased in CS-deficient patients. Hypermethioninaemia can originate also from liver disease, tyrosinaemia type I (McKusick 276700), or the ingestion of D-methionine or 6-azauridine. It can occur transiently in young children on high-protein diets, or be persistent with normal hepatic MAT, with or without myopathy, in association with high folate levels (Mudd et al 1989). A single patient with persistent hypermethioninaemia, normal hepatic MAT and normal folate levels has been reported with developmental delay and failure to thrive (Jhaveri et al 1982). Recently, a pedigree was described with hypermethioninaemia, decreased hepatic adenosylhomocysteine hydrolase (EC 3.3.1.1) activity and severe clinical manifestations, including failure to thrive, mental and motor retardation, facial dysmorphisms, and cardiomyopathy (Labrune et al 1990). All three defined defects of methionine catabolism are considered to be inherited as autosomal recessive traits. In the present report, we describe our investigation of a new form of persistent hypermethioninaemia inherited in a dominant fashion in three generations of one family.
I TRANSAMINATION 1 i PATHWAY I
TRANSSULFURATIONPATHWAY
J
iI '7
l
8
,3 i
1
i / CYSTEINE SULFATE
tranamlthylltlon
S-ADENOSYL- = HOMOCYSTE,NE
2
l9 3-METHYLTHIOPROPIONATE
[
[
~ S-ADENOSYLMETHIONINE
METHANETHIOL ! SULFATE o...o.o,ox,oE
DIMETHYLSULFIDE
Figure 1 Methionine metabolism: (1) methionine adenosyltransferase; (2) methyltransferase; (3) S-adenosylhomocysteine hydrolase; (4) betaine-homocysteine methyltransferase; (5) 5methyltetrahydrofolate-homocysteine methyltransferase; (6) cystathionine fl-synthase; (7) 7cystathionase; (8) transaminase; (9) branched-chain 2-oxoacid dehydrogenase J. Inher. Metab. Dis.
15 (1992)
190
Blom et al.
METHODS
Amino acids were quantitated using an LKB 4150 alpha plus amino acid analyser (LKB Biochrom, Ltd., Cambridge, UK). Heparinized plasma was deproteinized with 5% sulphosalicylic acid within 30min of collection, filtered through 0.22 #m Millipore membranes (Millipore Corp., Bedford, MA, USA), and stored at - 2 0 ° C prior to analysis. Urine samples were collected over 24 hours and also stored at - 2 0 ° C prior to analysis. Amino acids:
Methionine loading: After an overnight fast, an oral dose of 0.1 g L-methionine/kg body weight was administered to the two sisters, II-1 and II-2. Details of the loading procedure and control values in 23 healthy volunteers have been previously described (Blom et al i989a). Transamination metabolites: The transamination metabolites measured in urine and non-deproteinized serum consisted of 4-methylthio-2-oxobutyrate and methanethiol mixed sulphides. The assays in serum have been described previously (Blom et al 1989b). The sum of the concentrations of these metabolites represents a relative measure of the amount of methionine degraded via the transamination pathway (Gahl et al 1988; Blom et al 1989b).
Normal fibroblasts (GM 3651, GM 5659, GM 3440, GM 5757, GM 1501, GM 1489, GM 5758) were obtained from the Human Mutant Cell Repository (Camden, NJ, USA). As described previously (Blom et al 1990), fibroblasts were grown to confluence in Eagle's minimum essential medium containing 10% fetal bovine serum (Gibco, Grand Island, NY, USA), and harvested by trypsinization. Ceil culture:
Enzymes: Fibroblasts were washed three times and suspended in 0.1 mol/L KH2PO 4 (pH 7.4), sonicated, and centrifuged at 2500 g for 10 min. MAT and CS were assayed as described by Mudd et al (1965), with some modifications (Gahl et al 1987). Methylenetetrahydrofolate reductase (MTHFR, EC 1.1.99.15) was assayed according to Finkelstein et al (1978). Protein was measured by the Bio-Rad protein assay.
FAMILY REPORT
Two caucasian male first cousins (III-1, III-2) were ascertained by the presence of hypermethioninaemia on neonatal screening for CS deficiency. Because their hypermethioninaemia persisted during the first year of life, fluctuating between 87 and 475 #mol/L (Table 1), they and other family members were further investigated. Figure 2 gives the family pedigree. The probands' mothers (II-1 age 31, and II-2 age 30) were sisters and they and their father (I-1 age 53) also exhibited hypermethioninaemia (Table 2). The sisters' mother (I-2), one brother (II-4), and the husband (II-3) of II-2 were tested for hypermethioninaemia and found to be normal. Another brother (II-5) died of astrosarcoma at age 25 years. Urinary excretion of methionine was normal in all family members tested (Table 2). Recently, II-2 gave birth to a second body (III-3), who was also positive for hypermethioninaemia on neonatal screening. J. Inher. Metab. Dis. 15 (1992)
191
Dominant Hypermethioninaemia
Table 1 Plasma methionine concentrations of III-1 and III-2 in their first 2 years of life Age
(months) 0 1 2 3 4 7 8 9 10 20
Plasma methionine (#mol/L) III-1
111-2
475 474 277 209 87 152 161
176 389 358 138 t98 173 221
I
II
Ill Figure 2 Pedigree of the hypermethioninaemic family, showing a pattern of dominant inheritance. II-5 died of astrosarcoma
On physical examination, both the mothers (II-1 and II-2) and their children (III1 and iII-2), who were seen on several occasions during their first year of life, were normal, with no hepatomegaly. All ate normal diets with normal protein intakes. There was no history of liver disease, hepatitis, transfusions, exposure to hepatotoxins, or manifestations suggestive of thromboembolic events. They were receiving no medications, in particular no 6-azauridine. There was no history of consanguinity. The children's birth, growth, and development were entirely normal. None of the affected family members showed the fetor due to increased dimethylsulphide expiration associated with extensive methionine degradation via the transamination pathway (Gout et al 1975; Gaht et al 1988; Blom et al 1989b). Homocytine, cystathionine, cystine and tyrosine concentrations were normal in plasma and urine of the probands and their mothers and in the plasma of III-3 and of I-1. Routine liver function tests including alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase and gammaglutamyltranspeptidase were normal for H I - I , II-1, III-2 and II-2.
d. Inher. Metab. Dis. 15 (1992)
192
Biota et al.
Table 2 Plasma and urine methionine in family members (Fig. 2) Methionine
III- 1 111-2 III-3 II-i II-2 II-4 1I-5 1-2 I- 1 Normal children Mean (n = 10) Range Normal adults Mean (n = 16) Range
Plasma
Urine
(/~mol/L)
(/zmol/24 h)
See Table 1 See Table 1 156 137, 77 104, 73 42 34 55 203
51 50 142 141 -
26 10-40
46 16-130
26 10-42
63 22-225
RESULTS AND DISCUSSION The cause of hypermethioninaemia in this kindred was investigated systematically. Generalized liver disease was ruled out by the normal liver function tests and normal tyrosine levels. No family member manifested hyperhomocystinaemia or any clinical symptoms of homocystinuria due to CS deficiency. Fibroblast CS activities of II-1 (9.2 nmol (rag protein)- i (135 rain)- 1) and II-2 (14.3 nmol (rag protein)- i (135 rain)- 1) were within the range of the four concurrently assayed normals (6.3, 6.6, 6.8 and 22.3 nmol (rag protein) -1 (135 rain)-1) and the CS activities of the probands III-I (56.7nmol (rag protein) -I (135rain) -1) and III-2 (31.1nmol (rag protein) -1 (135 rain)-1) were actually higher than the normal levels. These results prompted investigation of methionine catabolism, which occurs by either transamination or adenosylation and subsequent transsulphuration (Figure 1). Transsulphuration predominates in humans, although up to 20% of methionine degradation may occur via the transamination pathway in the presence of hepatic MAT deficiency (Gahl et al 1988; Blom et al 1989b). The ability of the two affected sisters to catabolize methionine was tested by loading them with 0.1 g L-methionine/kg body weight. In normal control subjects this produces a rapid increase in plasma methionine followed by a gradual decrease (Figure 3). In the two sisters (II-1 and II-2) plasma methionine concentrations rose more rapidly, but decreased very slowly, and remained more than three standard deviations above the normal mean 8 hours after loading (Figure 3). This resembled methionine loading tests for homozygote CS-deficient patients (Blom et al 198%). The transamination pathway was investigated by measuring the sum of two of its metabolites, 4-methylthio-2-oxobutyrate and methanethiol mixed disulphides (Gahl J. Inher. Metab. Dis. 15 (1992)
Dominant Hypermethioninaemia 2000
193
Plasma Methionine C o n c e n t r a t i o n
1000
/ ,'/I ~ T
-o
/,'N 0 0
(/zmol/I)
T
I
I
4
8
T i m e (h) Figure 3 Plasma methionine concentrations before (Oh) and after (1-8 h) oral L-methionine loading in 23 normals (+) and the two hypermethioninaemic women II-1 (O) and II-2 (O). Bars give SD of the mean et al 1988; Blom et al 1989b), in serum and urine. After an overnight fast, the serum levels for III-1, II-1, III-2 and II-2 (0.53, 0.48, 0.68 and 0.81 #mol/L) were within the normal range (0.32-1.20#mol/L, n--23). Urine levels were also normal in II-1 (1.1mmol/mol creatinine) and II-2 (2.2mmol/mol creatinine), and only slightly elevated in III-1 (3.9 mmol/mol creatinine) and III-2 (3.0mmol/mol creatinine). (The normal range is 0.7-2.1 mmol/mol creatinine, n = 23.) After a methionine load, the serum concentrations of the transamination metabolites remained normal for II-2 but for II-1 were more than three standard deviations above the normal mean 2-8 hours after loading (Figure 4). These findings confirm that the methionine transamination pathway was intact; any elevations probably reflect increased concentrations of the substrate, methionine. MAT deficiency could explain this family's hypermethioninaemia, although the patients' plasma methionine concentrations were lower than usually reported in MAT deficiency (Gout et al 1975; Finkelstein et al 1975; Gaull et al 1981a; Gahl et al 1988; Mudd et al 1989). Fibroblast MAT activities were normal in III-1 (2.8nmol (mg protein)- 1 (120 min)- 1) and II-1 (2.9 nmol (mg protein)- 1 (120 min)- 1 and slightly decreased in III-2 (1.Snmol (mg protein) -1 (120min) -1) and II-2 (2.2nmol (mg protein)-: (120min) -1. The values of four concurrently assayed normals were 2.5, 2.9, 3.6 and 3.8 nmol (mg protein)-1 (120 min)-1. The fibroblast isoenzyme of MAT differs in its genetic control from the hepatic isoenzymes which handle the bulk of the body's methionine adenosylation (Gahl et al 1988; Mudd et al 1989; Finkelstein 1990), so a partial hepatic MAT deficiency remains possible. The normal or only moderately elevated concentrations of transamination metabolites in our family compared with one MAT-deficient patient (Gahl et al 1988) correlated with the low degree of hypermethioninaemia. A liver biopsy, which does not appear medically J. lnher. Metab. Dis. 15 (1992)
Blom et al.
194
26
Transamination M e t a b o l i t e s (/~mol/I)
/,O/
~" ~'~ ~ , . . ~
/ 13
/
/
/
----i- . . . . . . 0
z~
8
T i m e (h) Figure 4 Serum transamination pathway metabolites before (Oh) and after (1-8h) oral L-methionine loading in 10 normal women (+) and the two hypermethioninaemicwomen II1 (O) and II-2 (O). Bars gives SD of the mean. (Normal men were excluded because of the observed difference in methionine catabolism via the transamination pathway between premenopausal women and young men after methionine loading. (Blom et al 1988)) indicated, could assess hepatic MAT activity as well as the concentration of Sadenosylmethionine, which, if decreased in the face of hypermethioninaemia, would virtually assure the presence of a functional MAT deficiency. Excessive remethylation of homocysteine, using either NLmethyltetrahydrofolate or betaine as methyl donor, offered an alternative explanation for the hypermethioninaemia in this family. The formation of NLmethyltetrahydrofolate by methylenetetrahydrofolate reductase (MTHFR) is inhibited by S-adenosylmethionine (Kutzbach and Stokstad 1967; Jencks and Matthews 1987), and the betaine-dependent methylation of homocysteine is inhibited by methionine (Finkelstein et al 1972; Finkelstein and Martin 1986). A failure of either of these regulatory inhibitions might lead to a higher steady-state level of methionine, despite a normal transsulphuration. Mean fibroblast MTHFR activities (_+_SD) of four affected family members (II-t, II-2, III-1 and III-2) were 4.2 4- 1.4 nmol (mg protein)- 1 h- 1 (range 3.0-5.8), compared with 6.5 + 2.0nmol (mg protein)-1 h-1 (range 4.4-8.3) for the four normal subjects. In the presence of 0.2 mmol/L S-adenosylmethionine, the mean activity of MTHFR (_ SD) of the family members was 64 + 12% of the uninhibited value; for controls it was 71 _+ 9% of the uninhibited value. This normal S-adenosylmethionine inhibition of MTHFR runs counter to the hypothesis that excess homocysteine remethylation occurred due to unregulated synthesis of 5-methyltetrahydrofolate.Betaine-homocysteine methyltransferase present in human liver (Ericson 1960; Finkelstein 1990) and kidney (Mudd et al 1970a; McKeever et al 1991) is not measurable in cultured human fibroblasts (Mudd et al 1970b). Therefore, its regulation could not be tested. J. lnher. Metab. Dis. 15 (1992)
Dominant Hypermethioninaemia
195
Four patients with hypermethioninaemia, apparently normal hepatic MAT activity, and increased folate concentrations have been reported. Ten-fold elevated serum folate concentrations were noted in three clinically normal hypermethioninaemic neonates by Tsuchiyama et al (1982), and elevated serum fotate concentrations were reported in a girl with persistent hypermethioninaemia accompanied by myopathy and poor mental development (Gaull et al 1981b). However, the serum folate levels of our patients III-1 and III-2 were 7.6ng/ml and 33.1 ng/ml, respectively (normal < 30 ng/ml), ruling out this type of hypermethioninaemia in the present family. We are left with a kindred in which benign hypermethioninaemia appears to be dominantly inherited. One possible explanation is that the affected family members are heterozygous for a mutation in the structural gene for hepatic MAT, which produces a deviant gene dosage effect upon the catalytic activity such that the heterozygote form has less than 50% of the normal activity but more than in previously described patients with severe deficiencies of hepatic MAT. Such a mutation would be consistent also with the moderately increased concentrations of transamination pathway metabolites in urine of III-1 and III-2, and in serum of II2 after methionine loading (Figure 4). Liver MAT exists in two forms, a dimer (~z) and a tetramer (~4) of the same subunit (Cabrero et al 1987). Negative functional interactions between mutant and normal subunits therefore provide one mechanism for the postulated deviant gene dosage effect. Cabrero et al (1988) reported that in human hepatic cirrhosis there is a specific loss of the tetramer as compared to the dimer, as well as a decrease in overall hepatic MAT activity and suggested that this decrease may explain the hypermethioninaemia of cirrhosis. The possibilities exist that a mutation in the structural gene for MAT, or in that for a currently hypothetical MAT-processing enzyme, might lead to a failure of conversion of the dimeric form of hepatic MAT to the tetrameric form. Further investigations into these possibilities and their functional implications await the availability of appropriate tissues for study. ACKNOWLEDGEMENT This project was supported in part by grant no. MCJ000252, US Department of Health & Human Services, Public Health Service, Bureau of Maternal and Child Health and Resources Development, a grant (RR-69) from the General Clinical Research Center Program, National Institutes of Health, Rockville, MD, USA and The Netherlands Heart Foundation. Dr Finkelstein is supported by grant DK-13048 from the National Institutes of Health and by the Medical Research Service, Department of Veterans Affairs. REFERENCES Blom HJ, Boers GJH, van den Elzen PAM, van Roessel JJM, Trijbels JMF, Tangerman A (1988) Differences between premenopausal women and young men in the transamination pathway of methionine catabolism, and the protection against vascular disease. Eur J Clin Invest 18:633-639 Blom HJ, Boers GHJ, Trijbets JMF, van Roessel JJM, Tangerman A (t989a) Cystathionine synthase deficient patients do not utilize the transamination pathway of methionine to reduce hypermethioninemiaand homocystinemia.Metabolism 38:577-582 J. Inher. Metab. Dis. 15 (1992)
196
Blom et al.
Blom H J, Boers GHJ, van den Elzen PAM, Gahl WA, Tangerman A (1989b) Transamination of methionine in humans. Clin Sei 76:43-49 Blom HJ, Andersson HC, Seppala R, Tietze F, Gahl WA (1990) Defective glucuronic acid transport from lysosomes of infantile free sialic acid storage disease fibroblasts. Biochem J 268:621-625 Boers GHJ, Smals AGH, Drayer JIM, Trijbets JMF, Leermakers AI, Kloppenborg PW (1983) Pyridoxine treatment does not prevent homocystinemia after methionine loading in adult homocystinuria patients. Metabolism 32:390-397 Cabrero C, Puerta J, Alemany S (1987) Purification and comparison of two forms of Sadenosyl-L-methionine synthetase from rat liver. Eur J Biochem 170:299-304 Cabrero C, Duce AM, Ortiz P, Alemany S, Mato JM (1988) Specific loss of the high-molecular weight form of S-adenosyl-S-methionine synthase in human liver cirrhosis. Hepatology 8: t530-1534 Ericson LE (1960) Betaine-homocysteine-methyl-transferases. I. Distribution in nature. Acta Chem Scand 14:2102-2112 Finkelstein JD (1990) Methionine metabolism in mammals. J Nutr Biochem 1:228-237 Finketstein JD, Martin JJ (1986) Methionine metabolism in mammals. Adaptation to methionine excess. J Biol Chem 261:1582-1587 Finkelstein JD, Harris BJ, Kyle WE (1972) Methionine metabolism in mammals: Kinetic study of betaine-homocysteine methyltransferase. Arch Biochem Biophys 153:320-324 Finkelstein JD, Kyle WE, Martin JJ (1975) Abnormal methionine adenosyltransferase in hypermethioninemia. Biochem Biophys Res Commun 66:149t-1497 Finkelstein JD, Martin JJ, Kyle WE, Harris BJ (1978) Methionine metabolism in mammals: Regulation of methylenetetrahydrofolate reductase content of rat tissues. Arch Biochem Biophys 181:153-160 Gahl WA, Finkelstein JD, Mullen KD et al (1987) Hepatic methionine adenosyltransferase deficiency in a 31-year-old man. Am J Hum Genet 40:39-49 Gahl WA, Bernardini I, Finkelstein JD et al (1988) Transsulfuration in an adult with hepatic methionine adenosyltransferase deficiency. J Ctin Invest 81:390-397 Gaull GE, Tallan HH, Lonsdale D, Przyrembel H, Schaffner F, von Bassewitz DB (1981a) Hypermethioninemia associated with methionine adenosyltransferase deficiency: clinical, morphologic, and biochemical observations on four patients. J Pediatr 98:734-741 Gaull GE, Bender AN, Vulovic D, Tallan HH, Schaffner F (1981b) Methioninemia and myopathy: a new disorder. Ann Neurol 9:423-432 Gout JP, Serre JC, Dieterlen M e t al (1975) Une nouvelle cause d'hypermethioninemie de l'enfant. Arch Franc Ped 34:416-423 Jencks DA, Matthews RG (1987) Allosteric inhibition of methylenetetrahydrofolate reductase by adenosylmethionine. J Biol Chem 262:2485-2493 Jhaveri BM, Buist NRM, Gaull GE, Tallan HH (1982) Intermittent hypermethioninemia associated with normal hepatic methionine adenosyltransferase activity: report of a case. J Inher Metab Dis 5:101-105 Kutzbach C, Stokstad ELR (1967) Feedback inhibition of methylene-tetrahydrofolate reductase in rat liver by S-adenosylmethionine. Biochim Biophys Acta 139:217220 Labrune P, Perignon JL, Rault M et al (1990) Familial hypermethioninemia partially responsive to dietary restriction. J Pediatr 117:220-226 McKeever MP, Weir DG, Molloy A, Scott JM (1991) Betaine-homocysteine methyltransferase: organ distribution in man, pig and rat and subcellular distribution in the rat. Clin Sci 81: 551-556 Mudd SH, Finkelstein JD, Irreverre F, Laster L (1965) Transsulfuration in mammals. Microassays and tissue distributions of three enzymes of pathway. J Biol Chem 240: 43824392 Mudd SH, Levy HL, Morrow G I I I (1970a) Deranged B~2 metabolism: Effects on sulfur amino acid metabolism. Biochem Med 4:193-214
J. tnher. Metab. Dis. 15 (1992)
Dominant Hypermethioninaemia
197
Mudd SH, Uhlendorf BW, Hinds KR (1970b) Deranged B12 metabolism: studies of fibroblasts grown in tissue culture. Biochem Med 4:215-239 Mudd SH, Skovby F, Levy HL et al (1985) The natural history of homocytinuria due to cystathionine fl-synthase deficiency. Am J Hum. Genet 37:1-31 Madd SH, Levy HL, Skovby F (1989) Disorders of transsulfuration. In Scriver LR, Beaudet AL, Sly WS, Valle D eds. The Metabolic Basis of Inherited Disease, 6th edn. New York: McGraw-Hill, 693-734 Tsuchiyama A Oyanagi K, Nakata F et al (1982) A new type of hypermethioninemia in neonates. Tohoko J Exp Med 138:281-288 Ueland PM, Refsum H (1989) Plasma homocysteine, a risk factor for vascular disease: plasma levels in health, disease, and drug therapy. J Lab Clin Med 114:473-501
J. Inher. Metab. Dis. 15 (1992) 197
© SSIEM and Ktuwer AcademicPublishers. Printed in the Netherlands BOOK
REVIEW
Peroxisomes
- a p e r s o n a l account. Frank Roels. VUB Press, Brussels, 1991, about
£13 This monograph by Professor Frank Roels describes his experiences with peroxisomes over a period of more than 20 years. The content is a personal view, but since he has been involved with peroxisomes as morphological curiosities, as markers of Zellweger syndrome by their absence, and in more recent years as indicators of peroxisomal dysfunction by their abnormal dimensions or shapes, it is a very valuable and readable text. The author draws together morphological, histochemical and biochemical evidence and relates this to function in the normal and in peroxisomal disorders, and to the biogenesis of peroxisomes. Some of the views expressed might be considered controversial but there are few people who have had such extensive peroxisomal experience, and the arguments should be taken seriously. This text, and the extensive reference list (around 400 references are cited) complements the recent article in the Journal (1991; 14: 853-857). It should be read by all who have even a passing interest in peroxisomes and metabolic disorders. The one question to which I failed to find the answer is "What happened when he kissed the toad?" B. D. Lake
J. Inher. Metab. Dis. 15 (1992)
