The molecular defect in propionic acidemia: Exon skipping caused by an 8-bp deletion from an intron in the PCCB allele

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Abstract
Propionic acidemia is an autosomal recessive metabolic disease resulting from a deficiency of propionyl CoA carboxylase (PCC) activity. To investigate the genetic basis of propionic acidemia, we isolated a cDNA encoding the precursor of the β subunit of human PCC (β PCC). The cloned cDNA sequence was 1,832 bp long and the open reading frame of 1,617 nucleotides encoded a polypeptide of 539 amino acids with a molecular mass of 58,202 Da. The human β PCC sequence shared a high degree of homology (91%) with the full-length cDNA of rat β PCC at the amino acid level; there were only 47 differences among 539 amino acid residues compared. Polymerase chain reaction amplification and sequencing of cDNA from a β subunit-deficient Japanese patient revealed a deletion of 101 nucleotides consisting of one exon from mature mRNA. This deletion resulted in a frameshift and a stop codon in the new frame. Analysis of the genomic DNA revealed a homozygous 8-bp deletion from bp3 to bp10 of the intron just downstream of the deleted exon. This deletion disrupted the consensus 5′ splice signal and led to exon skipping.