Genetic heterogeneity in propionic acidemia patients with alpha-subunit defects. Identification of five novel mutations, one of them causing instability of the protein

The inherited metabolic disease propionic acidemia (PA) can result from mut ations in either of the genes PCCA or PCCB, which encode the alpha and beta subunits, respectively, of the mitochondrial enzyme propionyl CoA-carboxyl ase. In this work we have analyzed the molecular basis of PCCA gene defects , studying mRNA levels and identifying putative disease causing mutations. A total of 10 different mutations, none predominant, are present in a sampl e of 24 mutant alleles studied. Five novel mutations are reported here for the first time. A neutral polymorphism and a variant allele present in the general population were also detected. To examine the effect of a point mut ation (M348K) involving a highly conserved residue, we have carried out in vitro expression of normal and mutant PCCA cDNA and analyzed the mitochondr ial import and stability of the resulting proteins. Both wild-type and muta nt proteins were imported into mitochondria and processed into the mature f orm with similar efficiency, but the mature mutant M348K protein decayed mo re rapidly than did the wild-type, indicating a reduced stability, which is probably the disease-causing mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.