Maternal homocystinuria: studies of an untreated mother and fetus

Potential Misdiagnosis of Hyperhomocysteinemia due to Cystathionine Beta-Synthase Deficiency During Pregnancy

Extreme hyperhomocysteinemia with low cystathionine and cysteine is virtually diagnostic of cystathionine beta-synthase (CBS) deficiency since remethylation defects and hypermethioninemia due to other inborn errors cause elevated serum cystathionine. However, a pregnant CBS deficient patient was found to have elevated cystathionine in addition to elevated total homocysteine and methionine at 23 weeks of gestation and post-delivery cystathionine decreased to the lower level of normal. A second patient with cystathionine values during gestation also showed a rise from the low pre-pregnant value to massive elevation by delivery. Her infant had severe hyperhomocysteinemia in cord blood with a massive elevation of cystathionine, S-adenosylmethionine, and S-adenosylhomocysteine. The infant corrected her homocysteine value by 2 months and is not affected. This data demonstrates that the fetus when exposed to high homocysteine and methionine has increased synthesis of cystathionine which cannot be cleared because the fetus lacks cystathionine gamma-lyase, and thus cystathionine is returned to the mother's circulation. This situation could lead to a misdiagnosis of the cause of hyperhomocysteinemia in a previously undiagnosed pregnant CBS deficient patient. Assays combining homocysteine with cystathionine measurements are commonly available from commercial laboratories in the USA. The recognition of CBS deficiency vs. remethylation disorders is important in order to maximize treatment. The cord blood values revealed a major disturbance in methionine metabolism including a potential for impaired transmethylation reactions in the fetus due to the buildup of S-adenosylhomocysteine. It is possible that monitoring maternal cystathionine during gestation could provide another measure of fetal exposure to homocysteine.

Maternal homocystinuria and Moebius syndrome? Vascular aetiology

A case of Moebius syndrome is reported in an infant of a mother known to have pyridoxine-unresponsive homocystinuria. The authors suggest that Moebius syndrome could result from early vascular insufficiency or disruption occurring early in development related to maternal homocystinuria. Moebius syndrome consists of congenital complete or partial facial nerve palsy with or without paralysis of other cranial nerves and often in association with other malformations of the limbs and orofacial structures, but usually without gross structural brain abnormalities.

Maternal homozygosity for the common MTHFR mutation as a potential risk factor for offspring with limb defects

A common mutation, C677T, in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene leads to altered homocysteine metabolism, and has been associated with the occurrence of neural tube defects (NTD). Administration of folic acid decreases this risk. There is also evidence that periconceptional supplementation of mothers with folic acid can decrease the risk of limb defects in the offspring. Here we describe a child with a transverse terminal defect of one hand, whose mother is homozygous for the C677T MTHFR mutation. We suggest that homozygosity for the MTHFR mutation may be a risk factor for transverse terminal limb defect/s by an effect mediated through altered folate and homocysteine metabolism. Further studies of mothers of infants with limb reduction defects for the MTHFR mutation may be of help in establishing this association. A simple intervention in the form of folic acid supplementation would be protective, should an association be established.

Inborn errors of metabolism and pregnancy

An increasing number of women with inborn errors of metabolism are now reaching child-bearing age. For certain disorders there are maternal risks associated with pregnancy. These may be related to an increased likelihood of metabolic decompensation (e.g. disorders of the urea cycle) or to increased stress to systems already compromised by disease (e.g. cardiomyopathy in GSD III). Detrimental effects upon the fetus may also be caused by maternal disease, as occurs with phenylketonuria, or from medication used to treat the mother's condition. Less commonly, fetal inborn errors may adversely effect the mother's health--e.g. fetal long-chain acyl-CoA dehydrogenase deficiency and the maternal HELLP syndrome (haemolysis, elevated liver enzymes and low platelets) and AFLP (acute fatty liver of pregnancy). Because of the rarity of individual disorders, our knowledge of risks associated with pregnancy is limited. Even for more common inborn errors such as phenylketonuria, there remain a number of questions that have not been fully answered.

Role of amniotic fluid homocysteine level and of fetal 5, 10-methylenetetrahydrafolate reductase genotype in the etiology of neural tube defects

A mutation in the gene 5,10-methylenetetrahydrofolate reductase (MTHFR), leading to altered homocysteine metabolism, has been identified in parents and fetuses with fetal neural tube defects. We sought to determine which is of greater importance in fetal neural tube defect formation: the fetal MTHFR mutation or elevated amniotic fluid homocysteine level. We retrieved stored amniotic fluid from cases of isolated fetal neural tube defect diagnosed from 1988 to 1998 (n = 80), and from normal controls matched for race, month and year of amniocentesis, and maternal age. The presence or absence of the 677C-->T mutation of MTHFR was determined and homocysteine levels were measured; cases and controls were compared. Significantly more cases than controls were heterozygous or homozygous for the 677C-->T MTHFR mutation (44% vs 17%, P < or = 0.001). Cases were also significantly more likely than controls to have an amniotic fluid homocysteine level above the 90th centile (>1.85 micromol per liter); 27% vs 10%, P = 0.02. Thirty one cases and 12 controls had an abnormal genotype; however, amniotic fluid homocysteine levels were not significantly different between these two groups (6/31, or 19% of cases had an elevated homocysteine compared to 1/12, or 8% of controls; P = 0.65). In contrast, 40 cases and 60 controls had a normal genotype; the neural tube defect cases had significantly higher homocysteine levels (13/40, or 32% of cases had an elevated homocysteine level compared to only 6/60, or 10% of controls; P = 0.008). Although both abnormal fetal MTHFR genotype and abnormal amniotic fluid homocysteine concentration are significantly associated with neural tube defects, the association with amniotic fluid homocysteine concentration is significant regardless of the fetal MTHFR genotype. The relationship between maternal and fetal homocysteine metabolism is complex.

Neural tube defects and elevated homocysteine levels in amniotic fluid

OBJECTIVE

Our purpose was to study maternal blood and amniotic fluid concentrations of homocysteine and relevant vitamins in relation to neural tube defects.

STUDY DESIGN

Concentrations of total homocysteine, folate, and vitamins B12 and B6 were measured in maternal blood and amniotic fluid of 27 women carrying a fetus with a neural tube defect and 31 control women carrying a healthy fetus.

RESULTS

The mean total homocysteine concentration in amniotic fluid of the study group was significantly higher than that of the control group. The mean concentrations of total homocysteine in blood and the vitamins folate, B12, and B6 in, respectively, blood and amniotic fluid were not significantly different between the groups. The mean concentrations of homocysteine and vitamin B6 were significantly lower in amniotic fluid than in blood in both groups, whereas vitamin B12 in amniotic fluid was higher than in blood.

CONCLUSION

These results support the hypothesis that at least the cause of a subset of neural tube defects could reside in a primary or secondary maternal or fetal derangement of homocysteine metabolism.

Cerebral infarction after caesarean section due to heterozygosity for homocystinuria; a case report

Eleven days after a caesarean section cerebral infarction was diagnosed. The underlying cause appeared to be a heterozygous form of homocystinuria. This inborn error in methionine metabolism increases the risk of premature arteriosclerosis, even in heterozygotes. The biochemical abnormalities can be prevented in most of the patients by treatment with vitamin B6 (pyridoxine).

Management of inborn errors of metabolism during pregnancy

An increasing number of women with inherited metabolic disorders survive, conceive and have children. In order to safeguard the health of the mother and the developing embryo, fetus, and newborn during pregnancy, delivery, and the neonatal period it is necessary to be aware of the range of metabolic disorders, the risks to mothers and children, and appropriate management strategies. The roles of the Paediatrician, Obstetrician and Dietitian in the management of Maternal Hyperphenylalaninaemia and phenylketonuria are reviewed.