Propionic acidemia : Molecular analysis of beta subnit deficient Japanese petients

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Propionic acidemia is a recessively inherited disorder of organic acid metabolism caused by deficiency of propionyl-CoA carboxylase (PCC) activity. Enxyme deficiency can result from mutations in either the alpha or the beta subunit. The human beta-PCC cDNA was sequenced in full and shown to encode a pre-beta subunit of 539 amino acids. Polymerase chain reaction amplification and sequencing of betaPCC cDNA from five beta-subunit deficient Japanese patients (cell no.83,187,212,276,338) revealed two missense mutations (C1283T, C493T), one nonsense mutation (C1495T) and two splicing mutations. The allele frequency of the C1283T mutation was 50% (5/10) in this study, and this mutation was not detected in 50 normal Japanese subjects. This suggests that the C1283T mutation causes disease, and may be a common mutation in Japanese propionic acidemia patients. Two deletions were found in the coding region of the beta-PCC cDNA.One is a 57-bp in-frame deletion between nucleothides 373 and 429, resulting in the deletion of 19 amino acids in the coding sequence in patient 187. Analysis of the genomic DNA from 187 revealed a 4-bp deletion from bp+3 to bp+6 of the downstream intron adjacent to the deleted exon. This deletion disrupted the consensus 5' splice signal (GTAAGT->GTGTTT) and led to exon skipping. The second deletion is a 101-bp deletion between nucleotides 1199 and 1299 in patient 338, which resulted in a frame shift and a stop codon in the new frame. Similar analysis of the genomic DNA from 338 revealed an 8-bp deletion from bp+3 to bp+10 of the donor splice site of the intron. This deletion also disrupted the consensus 5' splice signal (GTGAGG->GTCATG) and led to exon skipping.