Vivian E. Shih

Cystathionine β‐synthase mutations in homocystinuria

The major cause of homocystinuria is mutation of the gene encoding the enzyme cystathionine β‐synthase (CBS). Deficiency of CBS activity results in elevated levels of homocysteine as well as methionine in plasma and urine and decreased levels of cystathionine and cysteine. Ninety‐two different disease‐associated mutations have been identified in the CBS gene in 310 examined homocystinuric alleles in more than a dozen laboratories around the world. Most of these mutations are missense, and the vast majority of these are private mutations. The two most frequently encountered of these mutations are the pyridoxine‐responsive I278T and the pyridoxine‐nonresponsive G307S. Mutations due to deaminations of methylcytosines represent 53% of all point substitutions in the coding region of the CBS gene. Hum Mutat 13:362–375, 1999.

Homocystinuria associated with decreased methylenetetrahydrofolate reductase activity

Summary A new type of homocystinuria is described. A variety of evidence indicates that patients with this type of homocystinuria are not deficient in cystathionine synthase activity. Fibroblasts from these patients were unable to grow as rapidly as control fibroblasts if homocystine replaced methionine in the culture medium. N 5 -Methyltetrahydrofolate-homocysteine methyltransferase activity in these cells was not markedly decreased, whereas methylenetetrahydrofolate reductase activity was significantly below normal. A deficiency of this reductase activity can explain the biochemical abnormalities in these patients.

Sulfite Oxidase Deficiency

Abstract Study of a 4 1/2-year-old boy with the unusual combination of acute infantile hemiplegia, ectopia lentis and the absence of homocystinuria showed large amounts of abnormal sulfur-containin...

Glutaric acidemia A metabolic disorder causing progressive choreoathetosis

A boy with glutaric acidemia had psychomotor retardation first noted at age 6 months, recurrent metabolic acidosis, and a progressive quadriparesis with choreoathetosis. He died at age 31/2 years. Cultured skin fibroblasts lacked glutaryl-CoA dehydrogenase activity. There was a biochemical, but not a clinical, response to dietary restriction of lysine and tryptophan. The caudate and putamen of the brain showed severe loss of nerve cells and fibers with proliferation of astrocytes, as well as markedly reduced γ-aminobutyric acid and glutamate decarboxylase activity.

Isolated sulfite oxidase deficiency: a case report with a novel mutation and review of the literature.

Isolated sulfite oxidase deficiency is a rare but devastating neurologic disease that usually presents in early infancy with seizures and alterations in muscle tone. Only 21 cases have been reported in the literature. We report a case of a newborn infant boy with isolated sulfite oxidase deficiency who presented with generalized seizures on his fourth day of life. Plasma total homocysteine was not detectable. Urinary sulfite, thiosulfate, and S-sulfocysteine levels were elevated. The patient began a low-methionine and low-cysteine diet and was treated with thiamine and dextromethorphan. However, he became increasingly microcephalic and was severely developmentally delayed. Mutation analysis of the sulfite oxidase gene revealed that the patient was homozygous for a novel 4-base pair deletion, and both of his parents were found to be heterozygous carriers of the same deletion. We reviewed the clinical, biochemical, neuroradiologic, and neuropathologic features in all published cases of isolated sulfite oxidase deficiency. Seizures or abnormal movements were prominent features in all cases. Developmental delays were reported in 17 cases. Ectopia lentis was detected in 9 cases. Clinical improvement with dietary therapy was seen in only 2 patients, both of whom presented after the age of 6 months and had relatively mild developmental delays. Plasma or urinary S-sulfocysteine levels were elevated in all cases. Urinary sulfite was detected in all except 1 case. Cerebral atrophy and cystic encephalomalacia were observed with neuroradiologic imaging and were noted in all 3 postmortem reports of isolated sulfite oxidase deficiency. The main alternative in the differential diagnosis of isolated sulfite oxidase deficiency is molybdenum cofactor deficiency.

Sepsis due to Escherichia coli in neonates with galactosemia.

Galactosemia, an inborn error of galactose metabolism, is characterized by jaundice, weight loss, lethargy and vomiting in the neonate and by cataracts, mental retardation and cirrhosis in later in...

A six-month, placebo-controlled trial of D-cycloserine co-administered with conventional antipsychotics in schizophrenia patients.

Rationaled-Cycloserine, a partial agonist at the glycine site of the N-methyl-d-aspartate receptor, has demonstrated inconsistent efficacy for negative and cognitive symptoms of schizophrenia. The strongest evidence for efficacy has come from studies using d-cycloserine at a dose of 50 mg/day added to conventional antipsychotics in trials of 8 weeks duration or less.ObjectiveTo assess the efficacy for negative symptoms and cognitive impairment of d-cycloserine augmentation of conventional antipsychotics in a 6-month trial.MethodsFifty-five schizophrenia patients with prominent negative symptoms, treated with conventional antipsychotics, were randomly assigned to treatment with d-cycloserine 50 mg/day or placebo for 6 months in a double-blind, parallel group design.ResultsTwenty-six subjects completed the 6-month trial; drop-out rates did not differ between treatment groups. d-Cycloserine treatment did not differ from placebo treatment on any primary outcome measure at 8 or 24 weeks, including response of negative symptoms and performance on a cognitive battery. Serum d-cycloserine concentrations did not correlate with response of negative symptoms.Conclusiond-Cycloserine did not exhibit therapeutic effects in this trial, possibly reflecting the high drop-out rate, a narrow range of therapeutic serum concentrations, a modest magnitude of therapeutic effect for the selected outcome measures, or loss of efficacy over time. Because d-cycloserine is a partial agonist with relatively low affinity for the glycine site, the magnitude of potential therapeutic effect may be smaller than that achieved by the higher-affinity full agonists, glycine and d-serine.

Low Vitamin B6 but Not Homocyst(e)ine Is Associated With Increased Risk of Stroke and Transient Ischemic Attack in the Era of Folic Acid Grain Fortification

Background and Purpose— The introduction of cereal grain folic acid fortification in 1998 has reduced homocyst(e)ine (tHcy) concentrations in the US population. We performed a case-control study to determine the risk of stroke and transient ischemic attack (TIA) associated with tHcy and low vitamin status in a postfortification US sample. Methods— Consecutive cases with new ischemic stroke/TIA were compared with matched controls. Fasting tHcy, folate, pyridoxal 5′-phosphate (PLP), B12, and MTHFR 677C→T genotype were measured. Results— Mean PLP was significantly lower in cases than controls (39.97 versus 84.1 nmol/L, P <0.0001). After stroke risk factors were controlled for, a strong independent association was present between stroke/TIA and low PLP (adjusted odds ratio [OR], 4.6; 95% CI, 1.4 to 15.1;P <0.001) but not elevated tHcy (OR, 0.92; 95% CI, 0.4 to 2.1). Conclusions— Low B6 but not tHcy was strongly associated with cerebrovascular disease in this postfortification, folate-replete sample.

Fetal Fatty Acid Oxidation Defects and Maternal Liver Disease in Pregnancy

OBJECTIVE: The objective was to evaluate the relationships between all types of fetal fatty acid oxidation defects and maternal liver disease, including acute fatty liver of pregnancy and hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome. METHODS: This was a case–control study comparing fetal fatty acid oxidation defects to the outcome of maternal liver disease. Fifty case infants with fatty acid oxidation defects were identified, with 25 matched controls collected per case. This generated a total of 50 case infants and 1,250 control infants. Pregnancies were evaluated for the presence of maternal liver disease (comprised of acute fatty liver of pregnancy, HELLP syndrome, and preeclampsia evolving into HELLP syndrome) using a conditional logistic regression model. Subgroup analysis compared long chain to short and medium chain fatty acid defects. RESULTS: Maternal liver disease was noted in 16.00% of all fatty acid oxidation defect pregnancies compared with 0.88% in the general population (odds ratio 20.4, 95% confidence interval 7.82–53.2). These pregnancies demonstrated an 18.1-fold increase in maternal liver disease when compared with our matched population controls with unaffected fetuses. All classifications of fatty acid oxidation defects were at high risk of developing maternal liver disease. Long chain defects were 50 times more likely than controls to develop maternal liver disease and short and medium chain defects were 12 times more likely to develop maternal liver disease. CONCLUSION: Maternal liver disease is significantly higher across the entire spectrum of fatty acid oxidation defects pregnancies compared with the matched control population. Notably, there is significant risk to the pregnancies with fetuses affected with short and medium chain defects, not just those with fetal long chain fatty acid oxidation defects as previously reported. Future studies should examine the pathophysiology of all infant fatty acid oxidation defects and its implications for maternal liver disease for improved future health outcomes. LEVEL OF EVIDENCE: II-2

Benign Methylmalonic Aciduria

Methylmalonic aciduria due to methylmalonyl-CoA mutase deficiency is usually considered to be a serious, often life-threatening disease. However, through routine screening of urine in neonates or screening of siblings of clinically affected neonates, we have identified eight children who have a benign clinical variant of this disorder. Their urinary methylmalonic acid levels have ranged from 1.0 to 3.4 mg per milligram of creatinine, with serum values ranging from an undetectable level to 1.7 mg per deciliter (130 nmol per liter). The children have not received dietary or vitamin therapy, have had normal growth and development (age range, 18 months to 13 years), and have performed as well as their unaffected siblings on psychometric testing. These children have no evidence of a deficiency of vitamin B12, which acts as a cofactor with methylmalonyl-CoA mutase, and they did not respond to the administration of vitamin B12. Two siblings were found by complementation analysis to have a defect in the methylmalonyl-CoA mutase apoenzyme; complementation analysis was not performed on the other patients. We conclude that the clinical spectrum of methylmalonyl-CoA mutase deficiency is wider than indicated by previously reported cases.