Clinica Chimica Acta, 202 (1991) 141-148
141
0 1991 Elsevier Science Publishers B.V. All rights reserved 0009~8981/91/$03.50
CCA 05098
Raised urinary excretion of inorganic pyrophosphate in asymptomatic members of a hypophosphatasia kindred J.D. Macfarlane
I, B.J.H.M. Poorthuis 2, R.A. Mulivor and A.M. Caswell 4
’
Departments of’ Rheumatology and ’ Paediatrics and Clinical Genetics, University of Leiden (The Netherlands), ’ Coriell Institute for Medical Research, New Jersey (USA) and ’ Department of Biochemistry and Molecular Biology, University of Leeds, Leeds (UK)
(Received 19 November 1990; revision received 29 July 1991; accepted 5 August 1991) Key words: Heritable disorder; Genetics; Alkaline phosphatase:
Phosphate; Phosphoethanolamine
Summary We report the screening of an Anglo-Welsh kindred in which two children were affected by different clinical forms of hypophosphatasia. Among the clinically normal adult members of the kindred, a raised urinary concentration of pyrophosphate was the commonest biochemical abnormality. The concentration of phosphate in serum was elevated in only one adult member of the kindred, the mother of the propositus. Consanguinity in this kindred suggests probable recessive inheritance, and the obligate heterozygotes each exhibited a low serum AP activity plus one other biochemical abnormality indicative of a carrier state.
Introduction Hypophosphatasia (HP), an inherited disorder characterised by a lack of activity of the enzyme alkaline phosphatase (AP; EC 3.1.3.11, encompasses a spectrum of clinical presentations ranging from a severely undermineralized skeleton in utero to fractures in the adult [l]. Only the bone/liver/ kidney or tissue nonspecific isoenzyme (TNSAP) of AP is involved but disease severity in the paediatric forms seems to be better related (inversely) to the age at presentation than to the total
Correspondence to: Dr. J.D. Macfarlane, Department of Rheumatology, Gebouw 1, C2-Q, University Hospital, Postbus 9600, 2300 RC Leiden, The Netherlands.
142
AP activity in serum. These aspects and the related dental problems have been well reviewed [l-3]. Biochemical abnormalities associated with the reduced AP activity include increased concentrations of phosphoethanolamine (PEA) [1,4-61 and inorganic pyrophosphate (PPi) [7] in urine, of phosphate (Pi> in serum [8,9] and of PPi [lo-121 and pyridoxal 5’-phosphate [13] in the plasma. The inheritance of HP is usually considered to be autosomal recessive though analysis of some kindreds, particularly those with affected adults, would suggest a dominant pattern [14-161. It is possible that a different type of genetic mutation is present in these latter kindreds. However, understanding the pattern of inheritance of HP is difficult, partly because in many studies of kindreds, the clinical, biochemical and radiological changes in the relatives have not been adequately defined. Several biochemical measurements have been used in attempts to detect carriers of HP, including activity of AP in serum, and concentrations of PPi in plasma and of PPi in plasma and of PPi and PEA in urine [2,11]. The measurement of urinary PPi has the added attraction that it is apparently not influenced by other bone diseases or diet. In a study of the kindred of a patient with adult HP, we measured serum and leucocyte AP activities and urinary PPi and PEA concentrations, and observed that the urinary excretion of PPi appeared to be the most sensitive indicator of the carrier state [17]. Another recent study of the kindreds of several severely affected infants from a highly inbred Canadian Mennonite group suggests that an elevated serum Pi concentration is also a marker for carriers of HP [18]. However, it is not clear whether this abnormality is restricted to Canadian Mennonite carriers of HP and/or to carriers of the severest forms of HP. We here report biochemical studies of a further kindred in which we have assessed the usefulness of the urinary concentration of PPi and the serum concentration of Pi in the identification of putative carriers of HP. This kindred is of particular interest because there is evidence of inbreeding. Kindred
The propositus V 2 (see pedigree, Fig. 11, one of twins, was delivered by Caesarean section at 33 weeks of pregnancy after premature rupture of the membranes. She was grossly dysmorphic and died a few hours later from respiratory insufficiency. The diagnosis of HP was confirmed by the demonstration of a reduced serum AP activity, limb deformities and a typical histological picture. The other, dizygotic, twin has never shown clinical, biochemical or radiological evidence of HP and will not be considered further in this report. The diagnosis of HP in V 2 prompted re-evaluation of her elder brother V 1. He had failed to thrive from early infancy and at 16 months spontaneously lost a lower incisor. These problems together with developing skull abnormalities (frontal bossing) strongly suggested a diagnosis of HP, and subsequent biochemical studies showed a reduced serum AP activity, a raised serum Pi concentration and raised urinary concentrations of PEA and PPi (Table I). Radiographs showed premature fusion of the sagittal suture and metaphyseal irregularities at several sites in long bones.
* obligate hetermggotes l
see legend
Fig. 1. Pedigree of inbred kindred with hypophosphatasia. 0, identifies asymptomatic family members exhibiting two biochemical abnormalities compatible with hypophosphatasia carrier status.
TABLE I Biochemical investigations in a kindred with hypophosphatasia Family member
III III III III III III III III IV IV IV V
a b ’ d
1. 3. 5. 8. 9. 10. 11. 12. 1. 2. 3. 1.
Sex Age (yr)
F F M F F F F M F M F M
76 75 70 63 59 57 51 47 31 26 23 2
Serum AP, U/I Method A %TNSAP (M75-190) a (F68-211) 86.5 86.1 73.9 b 125.8 149.0 127.3 120.6 49.4 b 45.4 b 43.4 b 82.1 122.0 c
97.1 96.5 98.1 95.3 96.2 95.6 97.3 96.6 95.6 97.5 96.9
Method
Serum Pi
Urinary PEA
Urinary PPi
mmo’/’ (0.81-1.45)
~mol/mmol (< 11)
creatinine (
141
0 1991 Elsevier Science Publishers B.V. All rights reserved 0009~8981/91/$03.50
CCA 05098
Raised urinary excretion of inorganic pyrophosphate in asymptomatic members of a hypophosphatasia kindred J.D. Macfarlane
I, B.J.H.M. Poorthuis 2, R.A. Mulivor and A.M. Caswell 4
’
Departments of’ Rheumatology and ’ Paediatrics and Clinical Genetics, University of Leiden (The Netherlands), ’ Coriell Institute for Medical Research, New Jersey (USA) and ’ Department of Biochemistry and Molecular Biology, University of Leeds, Leeds (UK)
(Received 19 November 1990; revision received 29 July 1991; accepted 5 August 1991) Key words: Heritable disorder; Genetics; Alkaline phosphatase:
Phosphate; Phosphoethanolamine
Summary We report the screening of an Anglo-Welsh kindred in which two children were affected by different clinical forms of hypophosphatasia. Among the clinically normal adult members of the kindred, a raised urinary concentration of pyrophosphate was the commonest biochemical abnormality. The concentration of phosphate in serum was elevated in only one adult member of the kindred, the mother of the propositus. Consanguinity in this kindred suggests probable recessive inheritance, and the obligate heterozygotes each exhibited a low serum AP activity plus one other biochemical abnormality indicative of a carrier state.
Introduction Hypophosphatasia (HP), an inherited disorder characterised by a lack of activity of the enzyme alkaline phosphatase (AP; EC 3.1.3.11, encompasses a spectrum of clinical presentations ranging from a severely undermineralized skeleton in utero to fractures in the adult [l]. Only the bone/liver/ kidney or tissue nonspecific isoenzyme (TNSAP) of AP is involved but disease severity in the paediatric forms seems to be better related (inversely) to the age at presentation than to the total
Correspondence to: Dr. J.D. Macfarlane, Department of Rheumatology, Gebouw 1, C2-Q, University Hospital, Postbus 9600, 2300 RC Leiden, The Netherlands.
142
AP activity in serum. These aspects and the related dental problems have been well reviewed [l-3]. Biochemical abnormalities associated with the reduced AP activity include increased concentrations of phosphoethanolamine (PEA) [1,4-61 and inorganic pyrophosphate (PPi) [7] in urine, of phosphate (Pi> in serum [8,9] and of PPi [lo-121 and pyridoxal 5’-phosphate [13] in the plasma. The inheritance of HP is usually considered to be autosomal recessive though analysis of some kindreds, particularly those with affected adults, would suggest a dominant pattern [14-161. It is possible that a different type of genetic mutation is present in these latter kindreds. However, understanding the pattern of inheritance of HP is difficult, partly because in many studies of kindreds, the clinical, biochemical and radiological changes in the relatives have not been adequately defined. Several biochemical measurements have been used in attempts to detect carriers of HP, including activity of AP in serum, and concentrations of PPi in plasma and of PPi in plasma and of PPi and PEA in urine [2,11]. The measurement of urinary PPi has the added attraction that it is apparently not influenced by other bone diseases or diet. In a study of the kindred of a patient with adult HP, we measured serum and leucocyte AP activities and urinary PPi and PEA concentrations, and observed that the urinary excretion of PPi appeared to be the most sensitive indicator of the carrier state [17]. Another recent study of the kindreds of several severely affected infants from a highly inbred Canadian Mennonite group suggests that an elevated serum Pi concentration is also a marker for carriers of HP [18]. However, it is not clear whether this abnormality is restricted to Canadian Mennonite carriers of HP and/or to carriers of the severest forms of HP. We here report biochemical studies of a further kindred in which we have assessed the usefulness of the urinary concentration of PPi and the serum concentration of Pi in the identification of putative carriers of HP. This kindred is of particular interest because there is evidence of inbreeding. Kindred
The propositus V 2 (see pedigree, Fig. 11, one of twins, was delivered by Caesarean section at 33 weeks of pregnancy after premature rupture of the membranes. She was grossly dysmorphic and died a few hours later from respiratory insufficiency. The diagnosis of HP was confirmed by the demonstration of a reduced serum AP activity, limb deformities and a typical histological picture. The other, dizygotic, twin has never shown clinical, biochemical or radiological evidence of HP and will not be considered further in this report. The diagnosis of HP in V 2 prompted re-evaluation of her elder brother V 1. He had failed to thrive from early infancy and at 16 months spontaneously lost a lower incisor. These problems together with developing skull abnormalities (frontal bossing) strongly suggested a diagnosis of HP, and subsequent biochemical studies showed a reduced serum AP activity, a raised serum Pi concentration and raised urinary concentrations of PEA and PPi (Table I). Radiographs showed premature fusion of the sagittal suture and metaphyseal irregularities at several sites in long bones.
* obligate hetermggotes l
see legend
Fig. 1. Pedigree of inbred kindred with hypophosphatasia. 0, identifies asymptomatic family members exhibiting two biochemical abnormalities compatible with hypophosphatasia carrier status.
TABLE I Biochemical investigations in a kindred with hypophosphatasia Family member
III III III III III III III III IV IV IV V
a b ’ d
1. 3. 5. 8. 9. 10. 11. 12. 1. 2. 3. 1.
Sex Age (yr)
F F M F F F F M F M F M
76 75 70 63 59 57 51 47 31 26 23 2
Serum AP, U/I Method A %TNSAP (M75-190) a (F68-211) 86.5 86.1 73.9 b 125.8 149.0 127.3 120.6 49.4 b 45.4 b 43.4 b 82.1 122.0 c
97.1 96.5 98.1 95.3 96.2 95.6 97.3 96.6 95.6 97.5 96.9
Method
Serum Pi
Urinary PEA
Urinary PPi
mmo’/’ (0.81-1.45)
~mol/mmol (< 11)
creatinine (
