CblE type of homocystinuria: mild clinical phenotype in two patients homozygous for a novel mutation in the MTRR gene

Patients with the cblE type of homocystinuria usually present with megaloblastic anaemia, feeding difficulties, developmental delay and cerebral atrophy. We present a 14-year-old Spanish girl (patient 1) and a 10-year-old Portuguese boy (patient 2) with cblE disease and mild clinical phenotype. The main clinical feature in both patients was persistent megaloblastic anaemia observed at 3 years and at 2 months of age, respectively. Diagnosis was made at the ages of 9 and 7 years, respectively, owing to persistent macrocytosis despite cobalamin treatment. Plasma total homocysteine values at diagnosis were 91 μmol/L and 44 μmol/L, respectively, in the absence of methylmalonic aciduria. Neurological and neurophysiological examinations were normal except for two small lesions on brain MRI suggestive of ischaemia and slight abnormalities in somatosensitive evoked potentials. Enzymatic analysis, complementation studies and clearly reduced production of methylcobalamin from ⁵⁷Co-labelled cyanocobalamin indicated functional methionine synthase reductase deficiency due to the cblE defect. Genetic analysis confirmed that both patients are homozygous for a novel mutation c.1361C > T in the methionine synthase reductase gene leading to a replacement of serine by leucine (S454L) in a highly conserved FAD-binding domain. We propose that homozygosity for this novel mutation may be associated with a mild phenotype, although its long-term deleterious neurological consequences remain possible. Furthermore, we propose that even in the absence of apparent neurological involvement, total homocysteine should be investigated in patients with resistant megaloblastic anaemia to detect possible mild forms of the cblE type of homocystinuria. This revised version was published online in August 2006 with corrections to the Cover Date.     

Delayed diagnosis of homocystinuria by major deficiency in cystathionine beta synthase

INTRODUCTION: Homocystinuria due to cystathionine beta synthase (CBS) deficiency is a special type of hyperhomocysteinemia because of its clinical expression (thrombotic events, ectopic lens and mental retardation). It's a rare, hereditary recessive autosomic disease generally diagnosed during childhood. EXEGESIS: Thrombophilia examination in a 50-year-old man found a dramatically increase homocysteinemia. Homocystinuria, profile of plasmatic amino acids and reduced CBS activity, (0.05 microkat/kg protein; N = 1.5 +/- 0.8) confirmed homocystinuria's diagnosis. Family study demonstrates that three siblings suffer from homocystinuria. Vitamin enriched diet with pyridoxin, vitamin B12 and folates induced reducing hyperhomocysteinemia and homocystinuria. CONCLUSION: This case report, original because of the diagnosis age, suggests a hyperhomocysteinemia's screening in patients with recurrent thrombotic events.     

Gene analysis and prenatal diagnosis for two families of congenital factor V deficiency

Summary. We studied two families in which the probands had severe bleeding tendency and showed low plasma levels of coagulation factor V (FV) antigen and activity. Sequence analysis of the FV gene on proband 1 demonstrated a novel G16088C homozygous missense mutation in exon 3 resulting in an Asp 68 to His substitution and on proband 2, a C69969T homozygous missense mutation in exon 23 leading to Gly2079Val. The parents of both families were each heterozygous for the corresponding FV gene defect. During their second pregnancy, the two families requested prenatal diagnosis. Chorionic villi were analysed at 12 weeks of gestation and cord blood samples were tested at 22 weeks. Microsatellite analysis performed in family 1 showed that the foetus sample was not contaminated by maternal tissue. The foetus 1 was found to be heterozygous for the familiar G16088C mutation with lower FV activity in the cord blood; the foetus 2 was a normal one. The diagnosis was confirmed after the birth. This is the first report of prenatal diagnosis for FV deficiency.     

Successful prenatal molecular diagnosis of carbamyl-phosphate synthetase I deficiency in two at-risk pregnancies

Summary We report the two first prenatal diagnoses in an Italian family with a proband affected by neonatal carbamyl-phosphate synthetase I deficiency in which molecular analysis identified V457G and Q810R amino acid substitutions. We performed a prenatal diagnosis on genomic DNA isolated from chorionic villus and amniotic fluid samples collected at 13 weeks of gestation. In the first pregnacy, the fetus was compound heterozygous for the mutations and termination of pregnancy was elected. The genetic lesions were also confirmed on genomic DNA isolated from the fetus’s liver and skin fibroblasts. A few months later, we performed a second prenatal diagnosis in this family. The second fetus was heterozygous for the wild-type alleles. The pregnancy was continued and a girl was born at 41 weeks of gestation. We have confirmed the wild-type state on the baby’s DNA.     

Folate-responsive homocystinuria and megaloblastic anaemia in a female patient with functional methionine synthase deficiency (cblE disease)

This first detailed report of a female patient with functional methionine synthase deficiency due to the cblE defect describes treatment with several vitamins and cofactors and clinical progress for 17 years. Before treatment, major findings were microcephaly, psychomotor retardation, episodic reduced consciousness, megaloblastic anaemia, increased plasma free homocystine (> 20 µmol/L), low plasma methionine (< 10 µmol/L) and increased excretion of formiminoglutamate. On high-dose folic acid, biochemical abnormalities such as formiminoglutamate excretion and homocystinuria nearly normalized, but clinical and haematological abnormalities remained. On replacement of folate with methylcobalamin, alertness, motor function, speech and the electroencephalogram improved, biochemical features were similar, but the mean corpuscular volume increased. The best control was observed on a combination of folate and methylcobalamin. At 17 years of age she remains severely mentally retarded.In cultured fibroblasts methionine synthesis was reduced (0.03 nmol/mg/per 16h, controls 2.4-6.9); methionine synthase activity was normal under high reducing conditions but decreased on limiting the reducing agent, dithiothreitol, to 5 mmol/L (18% of total, controls 51-81%); formation of methylcobalamin was low (4.5% of total cobalamins, control 57.5%) and complementation studies indicated the cblE defect. Methionine formation showed only minor increases in cells grown in folate- or cobalamin-supplemented medium. Serine synthesis, which was low in normal medium, increased with cobalamin supplementation. These studies suggest further heterogeneity within cblE mutants, show the difficulty of establishing the enzyme defect in vitro, and indicate a role for folate in addition to cobalamin in treatment.     

Cloning and mapping of a cDNA for methionine synthase reductase, a flavoprotein defective in patients with homocystinuria

Methionine synthase catalyzes the remethylation of homocysteine to methionine via a reaction in which methylcobalamin serves as an intermediate methyl carrier. Over time, the cob(I)alamin cofactor of methionine synthase becomes oxidized to cob(II)alamin rendering the enzyme inactive. Regeneration of functional enzyme requires reductive methylation via a reaction in which S-adenosylmethionine is utilized as a methyl donor. Patients of the cblE complementation group of disorders of folate/cobalamin metabolism who are defective in reductive activation of methionine synthase exhibit megaloblastic anemia, developmental delay, hyperhomocysteinemia, and hypomethioninemia. Using consensus sequences to predicted binding sites for FMN, FAD, and NADPH, we have cloned a cDNA corresponding to the “methionine synthase reductase” reducing system required for maintenance of the methionine synthase in a functional state. The gene MTRR has been localized to chromosome 5p15.2–15.3. A predominant mRNA of 3.6 kb is detected by Northern blot analysis. The deduced protein is a novel member of the FNR family of electron transferases, containing 698 amino acids with a predicted molecular mass of 77,700. It shares 38% identity with human cytochrome P450 reductase and 43% with the C. elegans putative methionine synthase reductase. The authenticity of the cDNA sequence was confirmed by identification of mutations in cblE patients, including a 4-bp frameshift in two affected siblings and a 3-bp deletion in a third patient. The cloning of the cDNA will permit the diagnostic characterization of cblE patients and investigation of the potential role of polymorphisms of this enzyme as a risk factor in hyperhomocysteinemia-linked vascular disease.     

Methionine transamination in patients with homocystinuria due to cystathionine beta-synthase deficiency

To assess the ability of patients with homocystinuria due to cystathionine beta-synthase (CBS) deficiency to perform the reactions of the methionine transamination pathway, the concentrations of the products of this pathway were measured in plasma and urine. The results clearly demonstrate that CBS-deficient patients develop elevations of these metabolites once a threshold near 350 micromol/L for the concurrent plasma methionine concentration is exceeded. The absence of elevated methionine transamination products previously reported among 16 CBS-deficient B6-responsive patients may now be attributed to the fact that in those patients the plasma methionine concentrations were below this threshold. The observed elevations of transamination products were similar to those observed among patients with isolated hypermethioninemia. Plasma homocyst(e)ine did not exert a consistent effect on transamination metabolites, and betaine appeared to effect transamination chiefly by its tendency to elevate methionine. Even during betaine administration, the transamination pathway does not appear to be a quantitatively major route for the disposal of methionine.     

β-Glucuronidase deficiency: Enzyme studies in an affected family and prenatal diagnosis

A-glucuronidase deficiency found in serum, leukocytes and fibroblasts and an increased [³⁵S]sulphate incorporation in fibroblasts led us to diagnose two cases of type VII mucopolysaccharidosis in one family. In spite of the wide distribution of activities in serum from controls, decreased-glucuronidase activity allowed us to demonstrate the heterozygous status of the parents and two other children. Following these studies, an antenatal diagnosis was performed when the mother was pregnant again; amniotic fluid and cultured amniotic cells were used for enzyme activity determination. A heterozygous fetus was suspected and confirmed after birth. The reliability of various biological materials for enzymatic diagnosis and existence of genetic variants in the normal population are discussed.     

Newborn screening, prenatal diagnosis, and prenatal treatment of congenital adrenal hyperplasia due to 21-hydroxylase deficiency.

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency can be detected by newborn screening. Benefits of screening for affected newborns include the prevention of severe adrenal crisis, its sequelae, and progressive signs of androgen excess. First-trimester prenatal diagnosis is possible by HLA typing and/or DNA analysis of genes within the HLA complex of chorionic villus cells; for second-trimester diagnosis, hormonal measurement o f amniotic fluid and HLA typing or DNA analysis of amniotic cells are used. Results of prenatal treatment of CAH have varied, and the efficacy of prenatal treatment by maternal glucocorticoid therapy requires further investigation.     

Pyrimidine 5'-nucleotidase deficiency: studies of five cases in two Japanese families

Two new families with red cell pyrimidine 5'-nucleotidase (P5N) deficiencies were found in Japan. The enzyme activities were 4.8% in case 1 and 9.7% in case 2. The propositi showed characteristic hemolytic anemia with market basophilic stippling, increased reduced glutathione content and accumulation of pyrimidine nucleotides in the red cell. High Michaelis constants for cytidine monophosphate, normal thermostability, abnormal optimum pH in both cases, and normal electrophoretic mobility in case 1 and slower mobility in case 2 were shown, suggesting that the cause of P5N deficiency, at least in these cases, is due to the structural gene mutation.     

Effects of polymorphisms of methionine synthase and methionine synthase reductase on total plasma homocysteine in the NHLBI Family Heart Study

The metabolism of homocysteine requires contributions of several enzymes and vitamin cofactors. Earlier studies identified a common polymorphism of methylenetetrahydrofolate reductase that was associated with mild hyperhomocysteinemia. Common variants of two other enzymes involved in homocysteine metabolism, methionine synthase and methionine synthase reductase, have also been identified. Methionine synthase catalyzes the remethylation of homocysteine to form methionine and methionine synthase reductase is required for the reductive activation of the cobalamin-dependent methionine synthase. The methionine synthase gene (MTR) mutation is an A to G substitution, 2756A-->G, which converts an aspartate to a glycine codon. The methionine synthase reductase gene (MTRR) mutation is an A to G substitution, 66A-->G, that converts an isoleucine to a methionine residue. To determine if these polymorphisms were associated with mild hyperhomocysteinemia, we investigated subjects from two of the NHLBI Family Heart Study field centers, Framingham and Utah. Total plasma homocysteine concentrations were determined after an overnight fast and after a 4-h methionine load test. MTR and MTRR genotype data were available for 677 and 562 subjects, respectively. The geometric mean fasting homocysteine was unrelated to the MTR or MTRR genotype categories (AA, AG, GG). After a methionine load, a weak positive association was observed between change in homocysteine after a methionine load and the number of mutant MTR alleles (P-trend=0.04), but this association was not statistically significant according to the overall F-statistic (P=0.12). There was no significant interaction between MTR and MTRR genotype or between these genotypes and any of the vitamins with respect to homocysteine concentrations. This study provides no evidence that these common MTR and MTRR mutations are associated with alterations in plasma homocysteine.     

Pendred syndrome in two Galician families: insights into clinical phenotypes through cellular, genetic, and molecular studies

CONTEXT: We studied two families from Galicia (northwest Spain) with Pendred syndrome (PS) and unusual thyroid phenotypes. In family A, the proposita had a large goiter and hypothyroxinemia but normal TSH and free T3 (FT3). In family B, some affected members showed deafness but not goiter. OBJECTIVE: Our objective was to identify the mutations causing PS and molecular mechanisms underlying the thyroid phenotypes. INTERVENTIONS: Interventions included extraction of DNA and of thyroid tissue. PATIENTS: Propositi and 10 members of the two families participated in the study. MAIN OUTCOME MEASURES: Main outcome measures included SLC26A4 gene analysis, deiodinase activities in thyroid tissue, and c.416-1G-->A effects on SLC26A4 splicing. In addition, a primary PS thyrocyte culture, T-PS2, was obtained from propositus B and compared with another culture of normal human thyrocytes, NT, by Western blotting, confocal microscopy, and iodine uptake kinetics. RESULTS: Proposita A was heterozygous for c.578C-->T and c.279delT, presented with goiter, and had normal TSH and FT3 but low FT4 attributable to high type 1 and type 2 iodothyronine deiodinase activities in the goiter. Propositus B bore c.279delT and a novel mutation c.416-1G-->A; some deaf relatives were homozygous for c.416-1G-->A but did not present goiter. The c.279delT mutation was associated with identical haplotype in the two families. T-PS2 showed truncated pendrin retained intracellularly and high iodine uptake with low efflux leading to iodine retention. CONCLUSIONS: c.279delT is a founder mutation in Galicia. Proposita A adapted to poor organification by increasing deiodinase activities in the goiter, avoiding hypothyroidism. Lack of goiter in subjects homozygous for c.416-1G-->A was due to incomplete penetrance allowing synthesis of some wild-type pendrin. Intracellular iodine retention, as seen in T-PS2, could play a role in thyroid alterations in PS.     

Hereditary non-spherocytic haemolytic anaemia due to red blood cell glutathione synthetase deficiency in four unrelated patients from Spain: clinical and molecular studies

In four unrelated patients with chronic haemolysis and markedly reduced red blood cell (RBC) glutathione (49.5%, 12.6%, 11.5% and 15% of the normal concentration respectively), a severe glutathione synthetase (GSH-S, EC 6.3.2.3) deficiency was found. One case exhibited a neonatal haemolytic anaemia associated with oxoprolinuria, but without neurological manifestations. The family study revealed GSH-S activity in both parents to be around half the normal level, a finding consistent with the presumed autosomal recessive mode of inheritance of this enzymopathy. Two cases exhibited a well-compensated haemolytic syndrome without anaemia or splenomegaly at steady state. One of these cases was diagnosed after an episode of acute haemolytic anaemia after fava bean ingestion. The remaining patient suffered from moderate to severe chronic non-spherocytic haemolytic anaemia and splenomegaly, and required occasional blood transfusion for a haemolytic crisis associated with drug ingestion. In this patient, the anaemia was corrected by splenectomy. In addition to GSH-S, a panel of 16 other RBC enzyme activities was also studied in all the patients. Hexokinase, aldolase, glucose-6-phosphate dehydrogenase and pyruvate kinase activities all increased; these increases were to be expected, given the rise in the number of circulating reticulocytes. In two patients, the incubation of RBCs with hydrogen peroxide revealed an enhanced production of malonyldialdehyde. DNA analysis showed a homozygous state for 656 A-->G mutation in patients 2 and 3. The GSH-S gene of patient 1, studied elsewhere, revealed an 808 T-->C. The GSH-S gene of patient 4 was not available for study. The present study demonstrates that GSH-S deficiency is also present in Spain and further supports the molecular and clinical heterogeneity of this enzymopathy     

The intellectual abilities of early-treated individuals with pyridoxine-nonresponsive homocystinuria due to cystathionine beta-synthase deficiency

The pathological sequelae of untreated homocystinuria due to cystathionine -synthase deficiency include ectopia lentis, osteoporosis, thromboembolic events and mental retardation. They occur at a significantly higher rate with poorer mental capabilities (mean IQ = 57) in the untreated pyridoxine-nonresponsive individuals. The mental capabilities of 23 pyridoxine-nonresponsive individuals with 339 patient-years of treatment were assessed using age-appropriate psychometric tests and were compared to those of 10 unaffected siblings (controls). Of the 23 individuals, 19 were diagnosed through newborn screening with early treatment, two were late-detected and two were untreated at the time of assessment. Thirteen of the newborn, screened group who were compliant with treatment had no complications, while the remaining 6, who had poor compliance, developed complications. Good compliance was defined by a lifetime plasma free homocystine median < 11 mol/L. The newborn screened, good compliance group (n = 13) with a mean age of 14.4 years (range 4.4–24.9) had mean full-scale IQ (FIQ) of 105.8 (range 84–120), while the poorly compliant group (n = 6) with a mean age of 19.9 years (range 13.8–25.5) had a mean FIQ of 80.8 (range 40–103). The control group (n = 10) with mean age of 19.4 years (range 9.7–32.9) years had a mean FIQ of 102 (range 76–116). The two late-detected patients aged 18.9 and 18.8 years had FIQ of 80 and 102, while the two untreated patients aged 22.4 and 11.7 years had FIQ of 52 and 53, respectively. There was no statistical evidence of significant differences between the compliant, early-treated individuals and their unaffected siblings (controls) except for the FIQ, which was significantly higher than that of the unaffected siblings (p = 0.0397). These data, despite the relatively small numbers, suggest that early treatment with good biochemical control (lifetime plasma free homocystine median < 11 mol/L) seems to prevent mental retardation.