Identification of three mutations and associated haplotypes in the protoporphyrinogen oxidase gene in South African families with variegate porphyria.

Mutation analysis of genomic DNA samples obtained from 17 unrelated South African patients with variegate porphyria (VP) revealed three novel missense mutations in the protoporphyrinogen oxidase (PPOX) gene. A common C to T transition at nucleotide position 452 (R59W) was identified in 15 of the patients analysed, while base changes at positions 336 (H20P) and 779 (R168C) were identified in the remaining two patients. Using protein analysis software we were able to predict that all three mutations have a similar biophysical effect on the protein, being the disturbance of amphiphatic regions within the protein, which might result in misfolding of the protein. Mutation R59W, identified in the majority of South African VP families, was shown to create a Styl restriction site, while mutation R168C would abolish a Dsal restriction site in genomic DNA of affected individuals. As 100% of the index patients analysed were molecularly characterized, the combined use of restriction enzyme and single-strand conformation polymorphism (SSCP) analysis now allows a rapid and accurate diagnosis of VP in South Africa. Mutation R59W was furthermore shown to be in association with one of four potential haplotypes defined by two newly described polymorphisms in exon 1 of the PPOX gene. Our molecular data thus strongly support the founder hypothesis for VP in South Africa.