2 ALPHA-SUBUNIT DONOR SPLICE-SITE MUTATIONS CAUSE HUMAN TRIFUNCTIONALPROTEIN-DEFICIENCY

Human trifunctional protein catalyzes three steps in mitochondrial P-o xidation of fatty acids, including the long chain 3-hydroxyacyl-CoA de hydrogenase step. Deficiency of this heterocomplex, which contains 4 a lpha and 4 beta subunits, causes sudden unexplained infant death, a Re ye-like syndrome, cardiomyopathy, or skeletal myopathy. We determined the molecular basis of this deficiency in a patient with neonatal pres entation and later sudden death using reverse transcription and PCR am plification of his alpha subunit mRNA. We demonstrated a universal del etion of exon 3 (71 bp) in his mRNA, This deletion causes a frameshift and very early premature termination, Amplification of genomic DNA de monstrated that the patient was a compound heterozygote with two diffe rent mutations in the 5' donor splice site following exon 3: a paterna lly inherited G to A transversion at the invariant position +1 and a m aternally inherited A to G mutation at position +3, Both allelic mutat ions apparently cause exon 3 skipping, resulting in undetectable level s of alpha subunit protein, and complete loss of trifunctional protein , This is the initial molecular characterization of trifunctional prot ein deficiency.