A putative exonic splicing enhancer in exon 7 of the PDHA1 gene affects splicing of adjacent exons.

A nonsense mutation (c.729C>A, Y243X) in exon 7 of the PDHA1 gene in a patient with pyruvate dehydrogenase deficiency results in aberrant splicing of the primary transcript with production of stable mRNAs which lack either both exons 6 and 7 or exon 7 alone. Transfection and expression of genomic constructs covering exons 5 to 8 of the mutant PDHA1 gene reproduced this aberrant splicing in vitro. The same pattern of abnormal splicing was found when a silent mutation was introduced at the same position. Both the nonsense and silent mutations alter a strong consensus site for the binding of SRp40, suggesting that they may interfere with an exonic splicing enhancer in exon 7 of the gene. However, this appears to affect splicing of not only exon 7, but also the adjacent upstream exon. The splice acceptor site of intron 5 has weak homology to the consensus sequence and this may contribute to the combined splicing defect.

Hyperinsulinism in short-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency reveals the importance of beta-oxidation in insulin secretion.

A female infant of nonconsanguineous Indian parents presented at 4 months with a hypoglycemic convulsion. Further episodes of hypoketotic hypoglycemia were associated with inappropriately elevated plasma insulin concentrations. However, unlike other children with hyperinsulinism, this patient had a persistently elevated blood spot hydroxybutyrylcarnitine concentration when fed, as well as when fasted. Measurement of the activity of L-3-hydroxyacyl-CoA dehydrogenase in cultured skin fibroblasts with acetoacetyl-CoA substrate showed reduced activity. In fibroblast mitochondria, the activity was less than 5% that of controls. Sequencing of the short-chain L-3-hydroxyacyl-CoA dehydrogenase (SCHAD) genomic DNA from the fibroblasts showed a homozygous mutation (C773T) changing proline to leucine at amino acid 258. Analysis of blood from the parents showed they were heterozygous for this mutation. Western blot studies showed undetectable levels of immunoreactive SCHAD protein in the child's fibroblasts. Expression studies showed that the P258L enzyme had no catalytic activity. We conclude that C773T is a disease-causing SCHAD mutation. This is the first defect in fatty acid beta-oxidation that has been associated with hyperinsulinism and raises interesting questions about the ways in which changes in fatty acid and ketone body metabolism modulate insulin secretion by the beta cell. The patient's hyperinsulinism was easily controlled with diazoxide and chlorothiazide.

Aortic stenosis in cardiovascular ochronosis.

Alkaptonuria (endogenous ochronosis) is a rare metabolic disorder caused by a deficiency of homogentisic acid oxidase, an enzyme responsible for the metabolic degradation of tyrosine. Patients with alkaptonuria commonly present with joint pain owing to degenerative arthritis. Other affected patients may present with pigmentation of the ear cartilage and sclera. This article reports a case of aortic stenosis associated with ochronosis in a 48-year-old man who presented with severe cardiac failure. He had no previous diagnosis of alkaptonuria, which was confirmed by mass spectrometry analysis of urine. The pathogenesis of cardiovascular ochronosis is unclear, but is probably related to the extensive extracellular deposits of ochronotic pigment in the cardiac tissue.

DOOR syndrome (deafness, onycho-osteodystrophy, and mental retardation): elevated plasma and urinary 2-oxoglutarate in three unrelated patients.

We describe three further children with the DOOR syndrome (deafness, onycho-osteodystrophy and mental retardation). A severe seizure disorder and characteristic facial appearance are part of the syndrome. Fourteen similar cases including the present patients are now on record. Autosomal recessive inheritance is likely. An increased level of 2-oxoglutarate in both plasma and urine has been found in our three patients. It is suggested there may be an inherited metabolic defect in this malformation syndrome.

Thin-layer chromatography of non-volatile organic acids in clinical chemistry.

The separation of biologically occurring non-volatile organic acids has been examined by thin-layer chromatography using a variety of solvent systems and thin-layer materials. The advantages of the two-dimensional method devised include the simultaneous demonstration of some keto acids as their oximes, sharp definition of the acidic spots, improved resolution over other published methods and rapid development. The method is very suitable for the biochemical diagnosis of known inborn errors of organic acid metabolism.

Successful reversal of propionic acidaemia associated cardiomyopathy: evidence for low myocardial coenzyme Q10 status and secondary mitochondrial dysfunction as an underlying pathophysiological mechanism.

Dilated cardiomyopathy is a rare complication in propionic acidaemia (PA). Underlying pathophysiological mechanisms are poorly understood. We present a child of Pakistani consanguineous parents, diagnosed with late-onset PA at 18months of age. He presented a mild phenotype, showed no severe further decompensations, normal growth and psychomotor development on a low protein diet and carnitine supplementation. At 15years, a mildly dilated left ventricle was noticed. At 17years he presented after a 2-3month history of lethargy and weight loss with severe decompensated dilated cardiomyopathy. He was stabilised on inotropic support and continuous haemofiltration; a Berlin Heart biventricular assist device was implanted. He received d,l-hydroxybutyrate 200mg/kg/day, riboflavin and thiamine 200mg/day each and coenzyme Q10 (CoQ10). Myocardial biopsy showed endocardial fibrosis, enlarged mitochondria, with atypical cristae and slightly low respiratory chain (RC) complex IV activity relative to citrate synthase (0.012, reference range 0.014-0.034). Myocardial CoQ10 was markedly decreased (224pmol/mg, reference range 942-2738), with a marginally decreased white blood cell level (34pmol/mg reference range 37-133). The dose of CoQ10 was increased from 1.5 to 25mg/kg/day. Cardiomyopathy slowly improved allowing removal of the external mechanical cardiac support after 67days. We demonstrate for the first time low myocardial CoQ10 in cardiomyopathy in PA, highlighting secondary mitochondrial impairment as a relevant causative mechanism. According to these findings, a high-dose CoQ10 supplementation could be a potential adjuvant therapeutic to be considered in PA-related cardiomyopathy.

Homozygous thermolabile variant of the methylenetetrahydrofolate reductase gene: a potential risk factor for hyperhomocysteinaemia, CVD, and stroke in childhood.

In this study of 118 children (median age 5.1 years; range 6 months to 17 years) with ischaemic stroke or transient ischaemic attack (TIA), 22 children (19%) were homozygous for the thermolabile variant of the methylenetetrahydrofolate reductase allele (t-MTHFR), compared with nine of 78 (12%) of a reference population (p=0.18, OR 1.76, 95% CI 0.76 to 4.04). Of those with cerebrovascular disease (CVD), 17 of 84 were homozygous for the t-MTHFR allele (p=0.13 compared with the reference population (OR 1.95, 95% CI 0.81 to 4.65). There was a significant (p<0.025) increment of plasma total homocysteine concentration in homozygotes for the t-MTHFR allele compared with heterozygotes, negatives for the t-MTHFR allele, and control children with no history of stroke. In four of 12 homozygotes for the t-MTHFR allele, plasma homocysteine levels were raised, compared with three of 38 of those who were negative or heterozygous (p=0.047; OR 5.8, 95% CI 1.1 to 31.2). Homozygotes for the t-MTHFR allele were significantly more likely to have a recurrent event than those who were negative or heterozygous (Cox regression p=0.031, hazard ratio 2.18, 95% CI 1.08 to 4.42). These data suggest that homozygosity for the t-MTHFR allele is associated with raised homocysteine levels in children and is a risk factor for primary and secondary stroke and TIA.

Short-chain 3-hydroxyacyl-CoA dehydrogenase deficiency associated with hyperinsulinism: a novel glucose-fatty acid cycle?

Hyperinsulinism of infancy is caused by inappropriate insulin secretion in pancreatic beta-cells, even when blood glucose is low. Several molecular defects are known to cause hyperinsulinism of infancy, such as K(ATP) channelopathies and regulatory defects of glucokinase and glutamate dehydrogenase. Although defects of fatty acid oxidation have not previously been known to cause hyperinsulinism, patients with deficiency in SCHAD (short-chain 3-hydroxyacyl-CoA dehydrogenase; an enzyme of mitochondrial beta-oxidation) have hyperinsulinism. A novel link between fatty acid oxidation and insulin secretion may explain hyperinsulinism in these patients.

Glycerol-3-phosphate excretion in fructose-1,6-diphosphatase deficiency.

A patient aged 23 months with fructose-1,6-diphosphatase deficiency is reported. This infant demonstrated an increased urine excretion of glycerol-3-phosphate during episodes of hypoglycaemia. The excretion of this compound has not previously been described in this disease or in those disorders associated with a deficiency in one of the other three gluconeogenic enzymes associated with hypoglycaemia. Its presence in the urine from patients may be useful in diagnosis.

The significance of a high plasma ammonia value.

At a tertiary referral centre, just over 50% of patients with plasma ammonia values over 200 micro mol/l had inborn errors of metabolism. To distinguish artefactual high values from those requiring treatment, the measurement should be repeated immediately if the result is above 200 micro mol/l and at lower concentrations if the patient is encephalopathic.

The adult presenting idiopathic Fanconi syndrome.

The adult presenting Fanconi syndrome is a rare familial disorder. A 30-year follow-up of one of the original families in the literature is reported here. Two important points have emerged. Firstly, the inheritance in this family is dominant, not recessive as originally suggested, and there remains no good example in the literature of a recessive inheritance of this disorder. Second, in this family lactic aciduria and tubular proteinuria are probably the earliest manifestations of the disorder in childhood, with glycosuria and aminoaciduria developing in the second decade and osteomalacia from the start of the fourth decade. Glomerular function deteriorates slowly but is compatible with a normal lifespan.

Hypoketotic hypofattyacidaemic hypoinsulinaemic hypoglycaemia in a child with hemihypertrophy? A new syndrome.

BACKGROUND: Recurrent and persistent hypoketotic, hypofattyacidaemic hypoglycaemia in infancy and childhood is most frequently due to hyperinsulinism of infancy. This biochemical profile can also be due to non-islet cell tumour hypoglycaemia or circulating insulin-receptor autoantibodies. Hyperinsulinaemic hypoglycaemia is also seen in children with the Beckwith-Wiedemann syndrome, where it is usually transient. METHODS/RESULTS: We report a novel case of child with hemihypertrophy and severe persistent hypoketotic, hypofattyacidaemic hypoinsulinaemic hypoglycaemia. No 'big' pro-IGF2 forms or circulating insulin-receptor antibodies were found. Glucose and protein isotope turnover studies showed marked suppression of hepatic glucose production during fasting. There was no evidence for constitutive autophosphorylation of the insulin or IGF-1 receptor, and no evidence for up-regulation of IGF-1 receptor. CONCLUSION: The precise pathophysiology of this novel case is still unclear.

Effect of exercise on protein turnover in man.

1. We have investigated the effects of moderate long-term exercise on protein turnover in fed man by measuring the extent of whole-body nitrogen production, the labelling of urinary ammonia from ingested [15N]glycine and plasma, muscle and urine free amino acid concentrations. 2. Judged both from nitrogen production, and from the extent of 13CO2 production from ingested L-[1-13C]leucine, exercise causes a substantial rise in amino acid catabolism. 3. Amino acids catabolized during exercise appear to become available through a fall in whole-body protein synthesis and a rise in whole-body protein breakdown. After exercise, protein balance becomes positive through a rise in the rate of whole-body synthesis in excess of breakdown. 4. Studies of free 3-methylhistidine in muscle, plasma and urine samples suggest that exercise decreases the fractional rate of myofibrillar protein breakdown, in contrast with the apparent rise in whole-body breakdown.