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 SouthAfrican patients with variegate porphyria (VP) revealed three novelmissense mutations in the protoporphyrinogen oxidase (PPOX) gene. A commonC to T transition at nucleotide position 452 (R59W) was identified in 15 ofthe patients analysed, while base changes at positions 336 (H20P) and 779(R168C) were identified in the remaining two patients. Using proteinanalysis software we were able to predict that all three mutations have asimilar biophysical effect on the protein, being the disturbance ofamphiphatic regions within the protein, which might result in misfolding ofthe protein. Mutation R59W, identified in the majority of South African VPfamilies, was shown to create a Styl restriction site, while mutation R168Cwould abolish a Dsal restriction site in genomic DNA of affectedindividuals. As 100% of the index patients analysed were molecularlycharacterized, the combined use of restriction enzyme and single-strandconformation polymorphism (SSCP) analysis now allows a rapid and accuratediagnosis of VP in South Africa. Mutation R59W was furthermore shown to bein association with one of four potential haplotypes defined by two newlydescribed polymorphisms in exon 1 of the PPOX gene. Our molecular data thusstrongly support the founder hypothesis for VP in South Africa.