Two a Subunit Donor Splice Site Mutations Cause Human Trifunctional Protein Deficiency

Human trifunctional protein catalyzes three steps in mito-chondrial,B-oxidation of fatty acids, including the long chain 3-hydroxyacyl-CoA dehydrogenase step. Deficiency of this heterocomplex, which contains 4a and 4.8 subunits, causes sudden unexplained infant death, a Reye-like syndrome, cardiomyopathy, or skeletal myopathy. We determined the molecular basis of this deficiency in a patient with neonatal presentation and later sudden death using reverse transcrip-tion and PCR amplification of his a subunit mRNA. We demonstrated a universal deletion of exon 3 (71 bp) in his mRNA. This deletion causes a frameshift and very early premature termination. Amplification of genomic DNA demonstrated that the patient was a compound heterozygote with two different mutations in the 5 ' donor splice site fol-lowing exon 3: a paternally inherited G to A transversion at the invariant position + 1 and a maternally inherited A to G mutation at position +3. Both allelic mutations apparently cause exon 3 skipping, resulting in undetectable levels of a subunit protein, and complete loss of trifunctional protein. This is the initial molecular characterization of trifunctiona