1328
of the n-6 type. There is observational evidence from studies in the Faroes that diets high in n-3 EFAs are associated with prolonged gestation and hence somewhat larger babies;4 conversely, women who ingested diets low in long-chain n-3 EFAs tended to be delivered earlier with smaller babies, although their diets were deficient in other respects as well.5 Progression from observation to intervention has shown clearly that diets high in n-3 EFAs are associated with prolongation of gestation. When pregnant rats were fed diets with a total EFA intake proportional to the minimum recommended and with either no n-3 EFAs or a proportion of fish oil, length of gestation was significantly prolonged in those receiving fish oil. 6,7 One study6 also reported prolongation of labour and consequently a higher stillbirth rate. A universal finding from rat pregnancy investigations was of a decreased birthweight after maternal fish oil ingestion during pregnancy.6-8 This year, Olsen et al9 reported a randomised control trial of dietary fish oil supplementation in human pregnancy; they found that gestation was significantly prolonged, by about 4 days, but that the birthweight of the babies was, if anything, slightly greater after maternal fish oil ingestion. These results could suggest either a species difference or a different mechanism for the two purpose
are
end-points. Administration of fish oil to pregnant rats was associated with reduction in the uterine concentration of PGE2.6PGE2is a potent inducer of parturition in women and has been used as such for more than 20 years. The events that lead up to the spontaneous onset of labour in women have still not been clarified, but PGs are almost certainly involved, at least as a secondary factor. A PG-associated mechanism might therefore contribute to the extended gestation. Renal PGE2 production was reduced in pregnant rats consuming fish oil, as has been reported in nonpregnant women taking dietary fish oil supplements.1o Under normal conditions PGE2 makes a limited contribution to maintenance of renal blood flow but this mechanism becomes more important under stress. 11 Does the lengthening of pregnancy by 4 days4,9 have any clinical relevance? It might. If a similar effect could be evoked acutely in threatened premature labour, this would give time for administration of steroids to accelerate pulmonary maturation. Rat pups whose dams had been fed a diet supplemented with fish oil showed some evidence of enhanced maturation of fetal lung phosphatidylcholine synthesis.8 If such an effect is not species specific, it might enhance the possibility of accelerated lung maturation. Nevertheless, we should remain cautious. An above normal bleeding time has been repeatedly found during ingestion of fish-rich diets12 by non-pregnant subjects, although no clinical abnormalities have been encountered. A fall in platelet count of between 4% and 35% has been observed in most studies ;13 such a
fall is likewise a sign of worsening pre-eclampsia, and could thus cause confusion, especially if fish oils were being used prophylactically against the condition. 14-17 Structure, biosynthesis and metabolism. In: Bygdeman M, Berger GS, Keith LG, eds. Prostaglandins and their inhibitors in clinical obstetrics and gynaecology. Lancaster: MTP, 1986: 13-26. 2. Leaf A, Weber PC. Cardiovascular effects of n-3 fatty acids. N Engl J Med 1988; 318: 549-57. 3. Thiery M, Amy JJ. Inhibition of labour. In: Bygdeman M, Berger GS, Keith LG, eds. Prostaglandins and their inhibitors in clinical obstetrics and gynaecology. Lancaster: MTP, 1986: 203-31. 4. Olsen SF, Hansen Hs, Sørensen TIA, et al. Intake of marine fat, rich in (n-3)-polyunsaturated fatty acids, may increase birthweight by prolonging gestation. Lancet 1986; ii: 367-69. 5. Crawford MA, Doyle W, Craft IL, Laurance BM. A comparison of food intakes during pregnancy and birthweight in high and low socioeconomic groups. Prog Lipid Res 1986; 25: 249-54. 6. Leaver HA, Lytton FD, Dyson H, Watson ML, Mellor DJ. The effect of dietary &ohgr;3 and &ohgr;6 polyunsaturated fatty acids on gestation, parturition and prostaglandin E2 in intrauterine tissues and the kidney. Prog Lipid Res 1986; 25: 143-46. 7. Olsen SF, Hansen HS, Jensen B. Fish oil versus arachis oil food 1. Green K.
supplementation in relation to pregnancy duration in rats. Prostaglandins Leukot Essent Fatty Acids 1990; 40: 255-60. 8. Clarke SD, Benjamin L, Bell L, Phinney SD. Fetal growth and fetal lung phospholipid content in rats fed safflower oil, menhaden oil or hydrogenated coconut oil. Am J Clin Nutr 1988; 47: 828-35. 9. Olsen SF, Sørensen JD, Secher NJ, et al. Randomised controlled trial of effect of fish-oil supplementation on pregnancy duration. Lancet 1992; 339: 1003-07.
Knapp HR, Fitzgerald GA. The antihypertensive effects of fish oil. N Engl J Med 1989; 320: 1037-43. 11. Lote C. Prostaglandins and the renal system. Prostaglandin Perspect 1988; 10.
4: 18-20. 12.
Rogers S, James KS, Butland BK, Etherington MD, O’Brien JR, Jones JG. Effects of a fish oil supplement on serum lipids, blood pressure, bleeding time and haemostatic and rheological variables. Atherosclerosis 1987; 63: 137-43.
Broughton Pipkin F. Fish-oil and pre-eclampsia. Br J Obstet Gynaecol 1991; 98: 737. 14. Secher NJ, Olsen SF. Fish oil and pre-eclampsia. Br J Obstet Gynaecol 13.
1990; 97: 1077-79. Gunn TR, Stewart IF. The control of gestational proteinuric hypertension with dietary marine lipids. Aust NZ J Med
15.
Starling MB,
16.
Dyerberg J, Bang HO. Pre-eclampsia and prostaglandins. Lancet 1985; i:
17.
Wang Y, Kay HH, Killam AP. Decreased levels of polyunsaturated fatty acids in preeclampsia. Am J Obstet Gynecol 1991; 164: 812-18.
1990; 20: 357. 1267.
Congenital bilateral absence of the vas deferens and cystic fibrosis Most males with cystic fibrosis have aspermia as a result of absence of the vas deferens. Congenital bilateral absence of the vas deferens (CBAVD) in healthy males without evidence of cystic fibrosis may be discovered during investigations for infertility, and accounts for 1-2% of male sterility 2,3 The frequency of unilateral congenital absence of the vas deferens is more difficult to ascertain, since fertility is usually unimpaired, but estimates from a series of vasectomies 4 suggest that 1-8 per thousand men are affected.4 Cystic fibrosis (CF) is the commonest severe autosomal recessive disorder in white populations, affecting 1 in 2500 live births. Sporadic cases of CBAVD have been recognised in otherwise healthy men, but the existence of 7 reported familial cases led to the suggestion that autosomal recessive inheritance might be important in this condition as well. Anguiano and colleagues5 now suggest that CBAVD
1329
may sometimes represent
a
very
mild, primarily
genital form of CF. There have been remarkable advances in knowledge of the gene causing CF since it
our was
mapped chromosome 7 and subsequently cloned.6°’ The gene extends over about 250 kb of genomic DNA, with 27 coding regions (exons). The messenger RNA, which is 6-2 kb long, contains an open reading frame capable of encoding a polypeptide of 1480 aminoacids. The CF gene protein product is called CFTR (cystic fibrosis transmembrane regulator). A specific deletion of three base-pairs in exon 10, found in nearly 70% of north European CF chromosomes, causes the loss of the aminoacid phenylalanine at position 508 (AF508). The most common half dozen mutations account for about 85% of north European CF chromosomes, and more than 150 other rarer to
mutations have been identified. The clinical course of CF can vary considerably, and the correlation of CF mutations with various phenotypes has been reported. Although there are exceptions,8 AF508 homozygosity is usually associated with severe disease, including pancreatic insufficiency. Other milder mutations seem to be dominant to OF508-ie, patients with AF508/nonAF508 or non-AF508/non-AF508 genotypes are less likely to have pancreatic involvement. The severity of lung disease is the main determinant of CF morbidity and mortality, but there is no clear correlation between genotype and lung function independent of pancreatic function. Dumar and colleagues9,lo reported the results of AF508 screening in men presenting with azoospennia and aplasia of the epididymis and vas deferens. 8 of the 19 patients were heterozygous for the AF508 deletion; all but 1 of the 8 had chronic sinusitis, and 2 patients had a raised sweat chloride concentration of almost 100 mmol/l. This frequency of AF508 heterozygosity was much higher than the expected population frequency of CF gene carriers (1 in 25), and led to speculation that these patients might have a different, as yet unidentified, CF mutation on the other allele, and effectively have a specific mild form of cystic fibrosis. Anguiano et a15 investigated 25 patients with CBAVD for six common CF mutations. 16 of the 25 men (64%) had at least one detectable CF mutation, sixteen times the expected population frequency. 13 patients were heterozygous for one CF mutation (AF508, G551D, Q493X, or Y9012X). The remaining 3 men were found to be compound
heterozygotes (with
different CF mutations on their chromosomes: AF508/D1270N in one case, and AF508/G576A in the other two). All 16 patients were essentially healthy: none has any manifestations of pulmonary disease or pancreatic insufficiency but some have chronic sinusitis. Sweat electrolytes were measured in 13 of these men-results were normal in 9, raised in 3, and equivocal in 1. 1 man had a distant cousin with history suggestive of CF, but the two
remaining patients had no family history of the disease. 1 patient (a AF508 heterozygote) had a brother with documented CBAVD, but no genotype is given for this sibling. If one combines the results of the two groups, 44 with CBAVD have been studied, 24 of whom have been shown to have at least one abnormal CF gene, including 3 who are known compound heterozygotes. Since a limited range of mutations has been tested for, it is very possible that other rare mutations remain undiscovered among this men
group.
There are several genetic implications that must be addressed. First, we need to consider the possibility of milder forms of CF in patients with symptoms such as chronic sinusitis or infertility as a result of CBAVD. DNA from such patients can be analysed for mutations in the CF gene. Any patients who are found to have CF, or to be CF carriers, will need careful genetic counselling, together with their partners, who could also be offered screening for CF carrier status. Spermatogenesis in men with CBAVD is normal, and sperm can be harvested microscopically from the epididymal remnant for use in in-vitro fertilisation programmes. However, if the man’s wife also carries a CF gene there will be a considerable risk of CF in any offspring. When the mutations are known in both partners, it will be possible to offer prenatal diagnosis by chorion villus biopsy at 10 weeks’ gestation. Nevertheless, in some cases it will be difficult to predict the likely severity of the disease in the fetus, especially when rarer mutations are involved. For these reasons, the continuing contribution to the International CF Consortium of genotype/phenotype correlations is very important. Male siblings of males with CBAVD due to CF have a 1 in 4 risk of being similarly affected, and counselling together with DNA analysis may be appropriate to circumvent the need for other investigations into infertility. now
1.
Kaplan E, Schwachman H, Perlmutter AD, Rule E, Khaw KT, Holsclaw OS. Reproductive failure in males with cystic fibrosis. N Engl J Med
1968; 279: 65-69. 2. Dubin L, Amelar RD. Etiologic factors in 1294 consecutive cases of male infertility. Fertil Steril 1971; 22: 469-74. 3. Jequier AM, Ansell ID, Bullimore NJ. Congenital absence of the vasa deferentia presenting with infertility. J Androl 1985; 6: 15-19. 4. Martin RA, Jones KL, Downey EC. Congenital absence of the vas deferens: recurrence in a family. Am J Med Genet 1992; 42: 714-15. 5. Anguiano A, Oates RD, Amon JA, et al. Congenital bilateral absence of the vas deferens: a primarily genital form of cystic fibrosis. JAMA 1992; 267: 1794-97. 6. Rommens JM, Ianuzzi MC, Kerem B, et al. Identification of the cystic fibrosis gene: chromosome walking and jumping. Science 1989; 245: 1059-65. 7. Riordan JR, Rommens JM, Kerem B, et al. Identification of the cystic fibrosis gene: cloning and characterisation of complementary DNA. Science 1989; 245: 1066-73. 8. Tizzano EF, Buchwald M. Cystic fibrosis: beyond the gene to therapy. J Pediatr 1992; 120: 337-49. 9. Dumar V, Gervais R, Rigot JM, et al. Abnormal distribution of CF &Dgr;F508 allele in azoospermic men with congenital aplasia of epididymis and vas deferens. Lancet 1990; 336: 512. 10. Rigot JM, Lafitte JJ, Dumar V, et al. Cystic fibrosis and congenital absence of the vas deferens. N Engl J Med 1991; 325: 64-65.
of the n-6 type. There is observational evidence from studies in the Faroes that diets high in n-3 EFAs are associated with prolonged gestation and hence somewhat larger babies;4 conversely, women who ingested diets low in long-chain n-3 EFAs tended to be delivered earlier with smaller babies, although their diets were deficient in other respects as well.5 Progression from observation to intervention has shown clearly that diets high in n-3 EFAs are associated with prolongation of gestation. When pregnant rats were fed diets with a total EFA intake proportional to the minimum recommended and with either no n-3 EFAs or a proportion of fish oil, length of gestation was significantly prolonged in those receiving fish oil. 6,7 One study6 also reported prolongation of labour and consequently a higher stillbirth rate. A universal finding from rat pregnancy investigations was of a decreased birthweight after maternal fish oil ingestion during pregnancy.6-8 This year, Olsen et al9 reported a randomised control trial of dietary fish oil supplementation in human pregnancy; they found that gestation was significantly prolonged, by about 4 days, but that the birthweight of the babies was, if anything, slightly greater after maternal fish oil ingestion. These results could suggest either a species difference or a different mechanism for the two purpose
are
end-points. Administration of fish oil to pregnant rats was associated with reduction in the uterine concentration of PGE2.6PGE2is a potent inducer of parturition in women and has been used as such for more than 20 years. The events that lead up to the spontaneous onset of labour in women have still not been clarified, but PGs are almost certainly involved, at least as a secondary factor. A PG-associated mechanism might therefore contribute to the extended gestation. Renal PGE2 production was reduced in pregnant rats consuming fish oil, as has been reported in nonpregnant women taking dietary fish oil supplements.1o Under normal conditions PGE2 makes a limited contribution to maintenance of renal blood flow but this mechanism becomes more important under stress. 11 Does the lengthening of pregnancy by 4 days4,9 have any clinical relevance? It might. If a similar effect could be evoked acutely in threatened premature labour, this would give time for administration of steroids to accelerate pulmonary maturation. Rat pups whose dams had been fed a diet supplemented with fish oil showed some evidence of enhanced maturation of fetal lung phosphatidylcholine synthesis.8 If such an effect is not species specific, it might enhance the possibility of accelerated lung maturation. Nevertheless, we should remain cautious. An above normal bleeding time has been repeatedly found during ingestion of fish-rich diets12 by non-pregnant subjects, although no clinical abnormalities have been encountered. A fall in platelet count of between 4% and 35% has been observed in most studies ;13 such a
fall is likewise a sign of worsening pre-eclampsia, and could thus cause confusion, especially if fish oils were being used prophylactically against the condition. 14-17 Structure, biosynthesis and metabolism. In: Bygdeman M, Berger GS, Keith LG, eds. Prostaglandins and their inhibitors in clinical obstetrics and gynaecology. Lancaster: MTP, 1986: 13-26. 2. Leaf A, Weber PC. Cardiovascular effects of n-3 fatty acids. N Engl J Med 1988; 318: 549-57. 3. Thiery M, Amy JJ. Inhibition of labour. In: Bygdeman M, Berger GS, Keith LG, eds. Prostaglandins and their inhibitors in clinical obstetrics and gynaecology. Lancaster: MTP, 1986: 203-31. 4. Olsen SF, Hansen Hs, Sørensen TIA, et al. Intake of marine fat, rich in (n-3)-polyunsaturated fatty acids, may increase birthweight by prolonging gestation. Lancet 1986; ii: 367-69. 5. Crawford MA, Doyle W, Craft IL, Laurance BM. A comparison of food intakes during pregnancy and birthweight in high and low socioeconomic groups. Prog Lipid Res 1986; 25: 249-54. 6. Leaver HA, Lytton FD, Dyson H, Watson ML, Mellor DJ. The effect of dietary &ohgr;3 and &ohgr;6 polyunsaturated fatty acids on gestation, parturition and prostaglandin E2 in intrauterine tissues and the kidney. Prog Lipid Res 1986; 25: 143-46. 7. Olsen SF, Hansen HS, Jensen B. Fish oil versus arachis oil food 1. Green K.
supplementation in relation to pregnancy duration in rats. Prostaglandins Leukot Essent Fatty Acids 1990; 40: 255-60. 8. Clarke SD, Benjamin L, Bell L, Phinney SD. Fetal growth and fetal lung phospholipid content in rats fed safflower oil, menhaden oil or hydrogenated coconut oil. Am J Clin Nutr 1988; 47: 828-35. 9. Olsen SF, Sørensen JD, Secher NJ, et al. Randomised controlled trial of effect of fish-oil supplementation on pregnancy duration. Lancet 1992; 339: 1003-07.
Knapp HR, Fitzgerald GA. The antihypertensive effects of fish oil. N Engl J Med 1989; 320: 1037-43. 11. Lote C. Prostaglandins and the renal system. Prostaglandin Perspect 1988; 10.
4: 18-20. 12.
Rogers S, James KS, Butland BK, Etherington MD, O’Brien JR, Jones JG. Effects of a fish oil supplement on serum lipids, blood pressure, bleeding time and haemostatic and rheological variables. Atherosclerosis 1987; 63: 137-43.
Broughton Pipkin F. Fish-oil and pre-eclampsia. Br J Obstet Gynaecol 1991; 98: 737. 14. Secher NJ, Olsen SF. Fish oil and pre-eclampsia. Br J Obstet Gynaecol 13.
1990; 97: 1077-79. Gunn TR, Stewart IF. The control of gestational proteinuric hypertension with dietary marine lipids. Aust NZ J Med
15.
Starling MB,
16.
Dyerberg J, Bang HO. Pre-eclampsia and prostaglandins. Lancet 1985; i:
17.
Wang Y, Kay HH, Killam AP. Decreased levels of polyunsaturated fatty acids in preeclampsia. Am J Obstet Gynecol 1991; 164: 812-18.
1990; 20: 357. 1267.
Congenital bilateral absence of the vas deferens and cystic fibrosis Most males with cystic fibrosis have aspermia as a result of absence of the vas deferens. Congenital bilateral absence of the vas deferens (CBAVD) in healthy males without evidence of cystic fibrosis may be discovered during investigations for infertility, and accounts for 1-2% of male sterility 2,3 The frequency of unilateral congenital absence of the vas deferens is more difficult to ascertain, since fertility is usually unimpaired, but estimates from a series of vasectomies 4 suggest that 1-8 per thousand men are affected.4 Cystic fibrosis (CF) is the commonest severe autosomal recessive disorder in white populations, affecting 1 in 2500 live births. Sporadic cases of CBAVD have been recognised in otherwise healthy men, but the existence of 7 reported familial cases led to the suggestion that autosomal recessive inheritance might be important in this condition as well. Anguiano and colleagues5 now suggest that CBAVD
1329
may sometimes represent
a
very
mild, primarily
genital form of CF. There have been remarkable advances in knowledge of the gene causing CF since it
our was
mapped chromosome 7 and subsequently cloned.6°’ The gene extends over about 250 kb of genomic DNA, with 27 coding regions (exons). The messenger RNA, which is 6-2 kb long, contains an open reading frame capable of encoding a polypeptide of 1480 aminoacids. The CF gene protein product is called CFTR (cystic fibrosis transmembrane regulator). A specific deletion of three base-pairs in exon 10, found in nearly 70% of north European CF chromosomes, causes the loss of the aminoacid phenylalanine at position 508 (AF508). The most common half dozen mutations account for about 85% of north European CF chromosomes, and more than 150 other rarer to
mutations have been identified. The clinical course of CF can vary considerably, and the correlation of CF mutations with various phenotypes has been reported. Although there are exceptions,8 AF508 homozygosity is usually associated with severe disease, including pancreatic insufficiency. Other milder mutations seem to be dominant to OF508-ie, patients with AF508/nonAF508 or non-AF508/non-AF508 genotypes are less likely to have pancreatic involvement. The severity of lung disease is the main determinant of CF morbidity and mortality, but there is no clear correlation between genotype and lung function independent of pancreatic function. Dumar and colleagues9,lo reported the results of AF508 screening in men presenting with azoospennia and aplasia of the epididymis and vas deferens. 8 of the 19 patients were heterozygous for the AF508 deletion; all but 1 of the 8 had chronic sinusitis, and 2 patients had a raised sweat chloride concentration of almost 100 mmol/l. This frequency of AF508 heterozygosity was much higher than the expected population frequency of CF gene carriers (1 in 25), and led to speculation that these patients might have a different, as yet unidentified, CF mutation on the other allele, and effectively have a specific mild form of cystic fibrosis. Anguiano et a15 investigated 25 patients with CBAVD for six common CF mutations. 16 of the 25 men (64%) had at least one detectable CF mutation, sixteen times the expected population frequency. 13 patients were heterozygous for one CF mutation (AF508, G551D, Q493X, or Y9012X). The remaining 3 men were found to be compound
heterozygotes (with
different CF mutations on their chromosomes: AF508/D1270N in one case, and AF508/G576A in the other two). All 16 patients were essentially healthy: none has any manifestations of pulmonary disease or pancreatic insufficiency but some have chronic sinusitis. Sweat electrolytes were measured in 13 of these men-results were normal in 9, raised in 3, and equivocal in 1. 1 man had a distant cousin with history suggestive of CF, but the two
remaining patients had no family history of the disease. 1 patient (a AF508 heterozygote) had a brother with documented CBAVD, but no genotype is given for this sibling. If one combines the results of the two groups, 44 with CBAVD have been studied, 24 of whom have been shown to have at least one abnormal CF gene, including 3 who are known compound heterozygotes. Since a limited range of mutations has been tested for, it is very possible that other rare mutations remain undiscovered among this men
group.
There are several genetic implications that must be addressed. First, we need to consider the possibility of milder forms of CF in patients with symptoms such as chronic sinusitis or infertility as a result of CBAVD. DNA from such patients can be analysed for mutations in the CF gene. Any patients who are found to have CF, or to be CF carriers, will need careful genetic counselling, together with their partners, who could also be offered screening for CF carrier status. Spermatogenesis in men with CBAVD is normal, and sperm can be harvested microscopically from the epididymal remnant for use in in-vitro fertilisation programmes. However, if the man’s wife also carries a CF gene there will be a considerable risk of CF in any offspring. When the mutations are known in both partners, it will be possible to offer prenatal diagnosis by chorion villus biopsy at 10 weeks’ gestation. Nevertheless, in some cases it will be difficult to predict the likely severity of the disease in the fetus, especially when rarer mutations are involved. For these reasons, the continuing contribution to the International CF Consortium of genotype/phenotype correlations is very important. Male siblings of males with CBAVD due to CF have a 1 in 4 risk of being similarly affected, and counselling together with DNA analysis may be appropriate to circumvent the need for other investigations into infertility. now
1.
Kaplan E, Schwachman H, Perlmutter AD, Rule E, Khaw KT, Holsclaw OS. Reproductive failure in males with cystic fibrosis. N Engl J Med
1968; 279: 65-69. 2. Dubin L, Amelar RD. Etiologic factors in 1294 consecutive cases of male infertility. Fertil Steril 1971; 22: 469-74. 3. Jequier AM, Ansell ID, Bullimore NJ. Congenital absence of the vasa deferentia presenting with infertility. J Androl 1985; 6: 15-19. 4. Martin RA, Jones KL, Downey EC. Congenital absence of the vas deferens: recurrence in a family. Am J Med Genet 1992; 42: 714-15. 5. Anguiano A, Oates RD, Amon JA, et al. Congenital bilateral absence of the vas deferens: a primarily genital form of cystic fibrosis. JAMA 1992; 267: 1794-97. 6. Rommens JM, Ianuzzi MC, Kerem B, et al. Identification of the cystic fibrosis gene: chromosome walking and jumping. Science 1989; 245: 1059-65. 7. Riordan JR, Rommens JM, Kerem B, et al. Identification of the cystic fibrosis gene: cloning and characterisation of complementary DNA. Science 1989; 245: 1066-73. 8. Tizzano EF, Buchwald M. Cystic fibrosis: beyond the gene to therapy. J Pediatr 1992; 120: 337-49. 9. Dumar V, Gervais R, Rigot JM, et al. Abnormal distribution of CF &Dgr;F508 allele in azoospermic men with congenital aplasia of epididymis and vas deferens. Lancet 1990; 336: 512. 10. Rigot JM, Lafitte JJ, Dumar V, et al. Cystic fibrosis and congenital absence of the vas deferens. N Engl J Med 1991; 325: 64-65.
