[Late onset 3-HMG-CoA lyase deficiency: a rare but treatable disorder]. / Déficit en 3-HMG-CoA lyase à révélation tardive : savoir reconnaître une maladie rare mais traitable.

3-Hydroxy-3-methylglutaric aciduria is a rare autosomal recessive genetic disorder due to a deficiency of the 3-hydroxy-3-methylglutarylCoA lyase (HMG-CoA lyase), a mitochondrial enzyme involved in ketogenesis and in the final step of l-leucine catabolism. HMG-CoA lyase deficiency can lead, in particular circumstances, such as fever, prolonged fasting or digestive disorders, to brutal and severe hypoglycemia with metabolic acidosis and sometimes fatal coma. We report on a new case of 3-hydroxy-3-methylglutaric aciduria particular by its late onset in a 3-year-old patient. Molecular investigation identified two new sequence modifications in the HMGCL gene: c.494G>A (p.Arg165Gln) and c.820G>A (p.Gly274Arg). We remind about this case report that the therapeutical is mainly preventive and allows a very good prognosis for this disease. Long-term treatment consists in limited fasting time, continuous low protein diet and l-carnitine supplementation. Preventive measures are essential: prevention of fasting and emergency treatment during intercurrent infections.

Metabolic studies in twin brothers with 2-methylacetoacetyl-CoA thiolase deficiency.

We report clinical and biological investigations in two patients (twin brothers) with 2-methylacetoacetyl-CoA thiolase deficiency. Main clinical features included important staturo-ponderal delay, frequent infectious rhinopharyngitis episodes and an acute metabolic acidosis at the age of 4 years, this metabolic decompensation being adequately halted by bicarbonate supplementation. Since that age, patients developed rather favorably, however, with persistence of the staturo-ponderal delay. Organicaciduria typical of 2-methylacetoacetyl-CoA thiolase deficiency was recorded consisting of excessive excretion of tiglylglycine, 2-methyl-3-hydroxybutyrate, 3-hydroxyisovalerate, 2-methylglutaconate, adipate and 2-methylacetoacetate. Blood carnitine levels were altered in patients with increased total and esterified carnitine concentrations and enhanced acyl/free carnitine ratios. Determination of acylcarnitine profiles showed that patients excreted excessive amounts of several acylcarnitines in urine including propionyl, butyryl, isobutyryl, isovaleryl, 2-methylbutyryl and tiglyl-carnitine, the latter acylcarnitine being prominent with, in one of the patients, occurrence of a previously undescribed isomer of this carnitine ester, possibly 2-ethylacrylyl-carnitine. Excretion of these acylcarnitines in urine was increased in response to L-carnitine although, as a whole, this therapy resulted in a less important stimulation of esterified carnitine removal in urine from patients than in the case of supplemented controls. Biochemical investigations on cultured skin fibroblasts confirmed 2-methylacetoacetyl-CoA thiolase deficiency. Through the present report on this rare disease in two siblings, we would like to underline that acylcarnitines can be used in the diagnosis of 2-methylacetoacetyl-CoA thiolase deficiency, a view supported by acylcarnitine profiles further determined in another patient with proven oxothiolase deficiency, adding this pathology to the list of beta-oxidation disorders that may be screened successfully through determination of acylcarnitine profiles in body fluids.

Retroviral-mediated gene transfer corrects very-long-chain fatty acid metabolism in adrenoleukodystrophy fibroblasts.

Adrenoleukodystrophy (ALD), a lethal demyelinating disease of the brain, is caused by mutations of a gene encoding an ATP-binding transporter, called ALDP, localized in the peroxisomal membrane. It is associated with a defective oxidation of very-long-chain fatty acids, leading to their accumulation in many tissues. This study reports that the retroviral-mediated transfer of the ALD cDNA restored very-long-chain fatty acid oxidation in ALD fibroblasts in vitro following abundant expression and appropriate targeting of the vector-encoded ALDP in peroxisomes. The same method may be used in hematopoietic cells as a further step of a gene therapy approach of ALD.