Atypical riboflavin-responsive glutaric aciduria, and deficient peroxisomal glutaryl-CoA oxidase activity: a new peroxisomal disorder

Investigation of cultured skin fibroblasts in a patient with atypical riboflavin-responsive glutaric acidura revealed a marked deficiency of peroxisomal glutaryl-CoA oxidase. This is the first patient to be reported with glutaric aciduria caused by a peroxisomal rather than a mitochondrial dysfunction. This enzyme appears to be specific for glutaryl-CoA, as lauryl-CoA and dodecanedioyl-CoA oxidase activities in the fibroblasts were both normal. The urinary excretion of glutaric acid (0.5 mmol mmol creatinine-1) suggests that the flux through this pathway is considerably less than the mitochondrial flux through glutaryl-CoA dehydrogenase. The elevated glutaric acid excretion (to 0.8 mmol mmol creatinine-1) in response to lysine loading suggests that lysine is a precursor.

Medium-chain acyl-CoA dehydrogenase deficiency: a useful diagnosis five years after death

We report a family in whom a fatal case of medium-chain acyl-CoA dehydrogenase (MCAD; EC 1.3.99.3) deficiency was diagnosed by enzymatic analysis of heart tissue that had been stored for five years. Three healthy siblings underwent subsequent investigation with the 3-phenylpropionic acid loading test. All siblings had been asymptomatic; however, one (age 2.5 years) excreted large amounts of 3-phenylpropionylglycine in response to the load and exhibited an organic aciduria consistent with the diagnosis of MCAD deficiency. The other two siblings did not demonstrate 3-phenylpropionylglycinuria after the loading test. This case underlines the importance of considering family history and using appropriate diagnostic tests in the recognition of hereditary metabolic disorders.

Medium-chain acyl-CoA dehydrogenase deficiency: a useful diagnosis five years after death

We report a family in whom a fatal case of medium-chain acyl-CoA dehydrogenase (MCAD; EC 1.3.99.3) deficiency was diagnosed by enzymatic analysis of heart tissue that had been stored for five years. Three healthy siblings underwent subsequent investigation with the 3-phenylpropionic acid loading test. All siblings had been asymptomatic; however, one (age 2.5 years) excreted large amounts of 3-phenylpropionylglycine in response to the load and exhibited an organic aciduria consistent with the diagnosis of MCAD deficiency. The other two siblings did not demonstrate 3-phenylpropionylglycinuria after the loading test. This case underlines the importance of considering family history and using appropriate diagnostic tests in the recognition of hereditary metabolic disorders.

Identification of a common mutation in patients with medium-chain acyl-CoA dehydrogenase deficiency

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is one of the most common recessively inherited metabolic diseases in man. We have studied fibroblast cultures obtained from three patients with MCAD deficiency by sequencing the entire coding region of MCAD mRNA. A single A to G nucleotide replacement which resulted in lysine329-to-glutamic acid329 substitution of the MCAD protein was identified in all cultures. Furthermore, this point mutation was present in 91% (31 of 34) of mutant MCAD alleles, indicating that the majority of cases with MCAD deficiency are caused by this type of mutation.

D(+)-glyceric aciduria: etiology and clinical consequences

A family comprising mother, father, and five children is described. Four of the children were found to excrete massive amounts of D(+)-glyceric acid in their urine. This was verified by gas chromatography-mass spectrometry and the configuration determined by capillary gas chromatography of O-acetylated menthyl esters. The excretion ranged from 10.8 to 19.9 mmol/24 h. The remaining child and the parents showed no evidence of this unusual metabolite. The virtual absence of clinical manifestations in this family was particularly interesting. Only two of the children showed any clinical abnormality and this was limited to mild microcephaly and speech delay; the other two children found to excrete large amounts of D(+)-glycerate were healthy and developmentally normal at 7 y and 9 y of age. There was a marked increase in the excretion rate of D(+)-glycerate in response to both oral fructose and serine loading. These results are consistent with a deficiency of D(+)-glycerate kinase and indicate the potentially benign nature of this disorder.

Trichothiodystrophy, mental retardation, short stature, ataxia, and gonadal dysfunction in three Moroccan siblings

Three sibs, a boy and two girls, born to Moroccan consanguineous parents, were affected with a syndrome characterized by brittle hair, mental retardation, short stature, ataxia, and gonadal dysfunction. The hair in these three patients displayed the morphological and biochemical hallmarks of trichothiodystrophy (TTD). Gonadal function tests showed abnormal gonadotropic responses to LHRH, consistent with delayed puberty in the male and ovarian failure in both females. Comparison with previously reported cases of TTD associated with mental retardation suggests genetic heterogeneity, although specific biochemical markers are needed in order to answer this question.

Analysis of abnormal urinary metabolites in the newborn period in medium-chain acyl-CoA dehydrogenase deficiency

In order to determine which are useful early diagnostic markers for medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, we have analysed urine from an asymptomatic neonate. Profiling of urinary organic acids followed by peak confirmation by electron impact mass spectrometry revealed a high suberate/adipate ratio (greater than 1.0) and the presence of n-hexanoylglycine (HG). Acylcarnitine analysis by fast atom bombardment mass spectrometry (FAB-MS) was inconclusive, but FAB-MS/MS (tandem mass spectrometry) revealed diagnostic amounts of octanoylcarnitine and hexanoylcarnitine. Quantitative analysis of acylglycines by stable isotope dilution and chemical ionization mass spectrometry revealed a 30-fold increase in HG and increased suberylglycine, but no increase in 3-phenylpropionylglycine.

A comparison of [9,10-3H]palmitic and [9,10-3H]myristic acids for the detection of defects of fatty acid oxidation in intact cultured fibroblasts

The production of tritiated water from [9,10-3H]myristic acid can be used as a screening assay for the detection of medium-chain acyl-CoA dehydrogenase deficiency, multiple acyl-CoA dehydrogenation defects (glutaric aciduria type 2 and ethylmalonic-adipic aciduria types), and some types of hydroxydicarboxylic aciduria. Comparison with the release of tritiated water from [9,10-3H]palmitic acid may give an indication of the chain-length specificity of the metabolic defect. In a case of ethylmalonic-adipic aciduria such a prediction has been confirmed by examination of accumulated intermediates in the affected fibroblasts.

Primary hyperoxaluria (L-glyceric aciduria) in the cat: a newly recognised inherited disease

The clinical features of a newly recognised inherited disease, primary hyperoxaluria in the cat, are reported. Affected cats developed acute renal failure between five and nine months old owing to the deposition of oxalate crystals in the tubules of the kidney. In addition to the signs attributable to kidney failure the affected animals became profoundly weak; there was evidence of denervation atrophy in skeletal muscle, and accumulations of neurofilaments were found in the proximal axons of the ventral horn cells and dorsal root ganglion cells of the spinal cord. Examination of urine from affected cats revealed L-glyceric aciduria and intermittent hyperoxaluria suggesting that the disease is a feline analogue of the human disorder, primary hyperoxaluria type 2. This supposition was confirmed by liver enzyme studies.

Disorders of mitochondrial beta-oxidation: prenatal and early postnatal diagnosis and their relevance to Reye's syndrome and sudden infant death

There are still many problems with the diagnosis and classification of inherited disorders of mitochondrial beta-oxidation. At present only the acyl-CoA dehydrogenase step of the beta-oxidation spiral has been explored in any detail and a large number of patients have disorders that cannot be properly characterized. beta-Oxidation defects may present in a wide variety of ways, the most dramatic being acute encephalopathy with hepatic involvement (atypical Reye's syndrome) or 'sudden' death. Investigations may include urinary and plasma organic acids, metabolic stress tests and assays of overall metabolic pathways or of specific enzymes in cultured fibroblasts, lymphocytes, or other material. Early postnatal diagnosis presents particular difficulties but in medium-chain acyl-CoA dehydrogenase deficiency the diagnosis may be apparent from careful examination of urine. There is as yet little general experience in prenatal diagnosis of this group of disorders except for glutaric aciduria type II. Single prenatal diagnoses of medium-chain acyl-CoA dehydrogenase deficiency and of an incompletely characterized defect of medium-chain fatty acid oxidation have been performed.

Family size limitation: a method for demonstrating recessive inheritance

Limitation of family size after the birth of a child with a serious disorder poses a problem in demonstrating autosomal recessive inheritance. In this paper methods are presented for distinguishing autosomal recessive inheritance given a 100% deterrent effect, and revealing a partial deterrent effect by analysis of sibship size and comparison with general population data. These methods are illustrated using information from phenylketonuria families.

Increased excretion of propan-1,3-diol and 3-hydroxypropionic acid apparently caused by abnormal bacterial metabolism in the gut

Three patients who died in infancy showed an unusual urinary organic acid pattern with excessive excretion of 3-hydroxypropionic acid but none of the other metabolites normally associated with propionyl-CoA carboxylase deficiency. Propan-1,3-diol was present in the urine in all three cases. In the two patients examined propionyl-CoA carboxylase activity was not deficient in cultured skin fibroblasts. A fourth patient, also severely ill, showed similar urinary abnormalities. Feeding a medium-chain triglyceride-rich diet to this patient increased the ratio of 3-hydroxypropionic acid to propan-1,3-diol and resulted also in the appearance of malonic acid in the urine. These abnormal metabolites disappeared on the administration of neomycin and presumably were produced by gut bacteria.

Methylmalonic semialdehyde dehydrogenase deficiency: demonstration of defective valine and beta-alanine metabolism and reduced malonic semialdehyde dehydrogenase activity in cultured fibroblasts

Intact cultured fibroblasts from a child with a new metabolic disorder, thought to be due to a deficiency of methylmalonic semialdehyde dehydrogenase, produced labeled CO2 normally from [1-14C]valine but not from [2-14C]valine. CO2 production from labeled beta-alanine was also much reduced, confirming the suspicion that malonic semialdehyde dehydrogenase is also deficient in this condition. An assay for malonic semialdehyde dehydrogenase in cell homogenates showed low activity but it was impossible to assess the degree of reduction.

Prenatal diagnosis of medium-chain acyl-coenzyme A dehydrogenase deficiency

A fatal case of medium-chain acyl-coenzyme A dehydrogenase deficiency is described in a patient who presented with hypoglycaemia and a gross non-ketotic dicarboxylic aciduria. Cultured skin fibroblasts released 14CO2 from [1-14C] octanoic acid at half the normal rate. Prenatal diagnosis was undertaken in a subsequent pregnancy in which cultured amniotic fluid cells revealed a marked reduction in octanoate oxidation indicative of an affected fetus. The pregnancy was terminated and the diagnosis was confirmed by enzyme analysis of skin fibroblasts taken from the fetus. The high residual octanoate oxidation by affected fibroblasts together with the absence of any characteristic abnormality of amniotic fluid organic acids are a potential limitation to the reliability of this type of prenatal diagnosis.

Urinary organic acids in succinic semialdehyde dehydrogenase deficiency: evidence of alpha-oxidation of 4-hydroxybutyric acid, interaction of succinic semialdehyde with pyruvate dehydrogenase and possible secondary inhibition of mitochondrial beta-oxidation

In addition to the previously reported abnormalities, urine extracts from three cases of succinic semialdehyde dehydrogenase deficiency have shown consistently increased amounts of 2,4-dihydroxybutyric acid, and its lactone, and 3-hydroxypropionic acid, metabolites related to the alpha-oxidation of 4-hydroxybutyric acid. Threo- and erythro-4,5-dihydroxyhexanoic acids have also been identified for the first time and probably arise from the reaction of succinic semialdehyde with an intermediate in the pyruvate dehydrogenase pathway. Adipic acid excretion is also consistently raised, suggesting secondary interference with mitochondrial beta-oxidation. The presence of these metabolites could be a source of diagnostic confusion.