PYRUVATE-DEHYDROGENASE DEFICIENCY - MOLECULAR-BASIS FOR INTRAFAMILIALHETEROGENEITY

Two half-brothers and their mother had symptomatic pyruvate dehydrogen ase complex deficiency. The infants had severe congenital lactic acido sis, seizures, and apneic spells and died at the ages of 3 and 4 month s. The mother was less symptomatic with mental retardation, truncal at axia, and dysarthria. The residual pyruvate dehydrogenase activities i n cultured skin fibroblasts from the 2 infants and their mother were 7 , 15, and 10% of control values. Immunoblot analysis showed negligible amounts of E1 alpha and E1 beta subunits of the complex. Northern blo t analysis for the E1 alpha subunit showed normal results. In the 2 so ns, complementary DNA sequence analysis revealed a cytosine to thymine mutation in exon 4, resulting in a change of arginine 127 to tryptoph an in the E1 alpha subunit. Restriction enzyme analysis of the polymer ase chain reaction product representing exon 4 of the E1 alpha gene re vealed that the mother was a heterozygote. Complementary DNA restricti on analysis and methylation analysis of the X chromosome DXS255 loci r evealed skewed activation of the mutant allele, consistent with the de ficient pyruvate dehydrogenase activity in the mother's fibroblasts. T he milder maternal phenotype is consistent with variable X-inactivatio n patterns in different organs of female heterozygotes.