Vockley, Jerry

Objective. 2-Methylbutyryl-CoA dehydrogenase deficiency, also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a recently described autosomal recessive disorder of l-isoleucine metabolism. Only 4 affected individuals in 2 families have been described. One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy. A sibling of the first patient is asymptomatic after prenatal diagnosis and early treatment. Family investigations in the second family revealed that the patient’s mother was also affected but asymptomatic. Methods. We report 8 additional patients identified by prospective newborn screening using tandem mass spectrometry. Results. Molecular genetic analysis performed for 3 of these patients revealed that all are homozygous for an 1165A>G mutation that causes skipping of exon 10 of the SBCAD gene. Although there was no obvious consanguinity, all patients belong to the Hmong, an ancient ethnic group that originated in China and constitutes only 0.8% and 0.6% of the Minnesota and Wisconsin population, respectively. Dietary treatment was initiated in the neonatal period. Except for 1 patient who developed mild muscle hypotonia, all patients remain asymptomatic at ages ranging from 3 to 14 months of age. Conclusions. These cases suggest that SBCAD deficiency is another inborn error of metabolism detectable by newborn screening using tandem mass spectrometry. The continued efficacy of long-term dietary therapy instituted presymptomatically remains to be established.

AbstractSummary: We report identification of short‐chain acyl‐CoA dehydrogenase (SCAD) deficiency in a 12‐year‐old boy who suffered from recurrent attacks of vomiting once or twice a year from infancy. Growth and development were normal and there were no muscular symptoms. Metabolic screening was performed during a hospitalization at 8 years of age and revealed an increased excretion of ethylmalonic acid (EMA; 45–80 mmol/mol creatinine, normal 0.2–6.6), suggesting a degradation defect of short‐chain fatty acids. An increased n‐butyrylcarnitine was found in freshly collected serum (0.9 µmol/L; normal <0.4) but not in dry blood spots. Neither of the frequent SCAD gene variants 625G>A and 511C>T was present, but direct sequencing of the promoter and coding regions of the SCAD gene revealed that the patient had mutations on both alleles: 417G>C (Trp115Cys) and 1095G>T (Gln341His). Neither mutation has been described before in compound heterozygosity or homozygosity. Enzymatic investigations subsequently confirmed a defect of SCAD in both fibroblasts and muscle extracts. Furthermore, expression studies of both mutations demonstrated impaired enzyme function or structure. To our knowledge, this case is the first description of a patient with proven SCAD deficiency presenting with recurrent emesis but without other symptoms, and emphasizes the wide clinical phenotype of this disorder.

Abnormalities of fatty acid metabolism are recognized to play a significant role in human disease, but the mechanisms remain poorly understood. Long-chain acyl-CoA dehydrogenase (LCAD) catalyzes the initial step in mitochondrial fatty acid oxidation (FAO). We produced a mouse model of LCAD deficiency with severely impaired FAO. Matings between LCAD +/− mice yielded an abnormally low number of LCAD +/− and −/− offspring, indicating frequent gestational loss. LCAD −/− mice that reached birth appeared normal, but had severely reduced fasting tolerance with hepatic and cardiac lipidosis, hypoglycemia, elevated serum free fatty acids, and nonketotic dicarboxylic aciduria. Approximately 10% of adult LCAD −/− males developed cardiomyopathy, and sudden death was observed in 4 of 75 LCAD −/− mice. These results demonstrate the crucial roles of mitochondrial FAO and LCAD in vivo .