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

Abstract

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.

Plasma Fluorescence Scanning and Fecal Porphyrin Analysis for the Diagnosis of Variegate Porphyria: Precise Determination of Sensitivity and Specificity with Detection of Protoporphyrinogen Oxidase Mutations as a Reference Standard

“…Identification of the cDNA for PPOX (18 ) and recognition that the founder R59W mutation accounts for 95% of all South African patients with VP (19,20 ) have enabled the assignment of an accurate genotypic diagnosis in our patients and has in turn allowed us to determine accurately the sensitivity and specificity of biochemical testing in our population. Our findings are reported here.…”

Extended Intermarker Linkage Disequilibrium in the Afrikaners

“…Although in more recent years some admixture has occurred, the population growth over 13-15 generations was almost entirely through reproduction, as immigration subsequent to the founding was minimal. The demographic history of this population is reflected in the unusually high frequency of certain rare Mendelian disorders, the unusually low diversity of the associated allelic variants, and the unusually large extent (8-11 cM) of conserved haplotypes around disease genes (Hayden et al 1980;Brink et al 1987;Rosendorff et al 1987;Leitersdorf et al 1989;Torrington and Viljoen 1991;Brink et al 1995;Pronk et al 1995;Goldman et al 1996;Warnich et al 1996;Groenewald et al 1998;Roby et al 1999).…”

Quantitative Structural Insight into Human Variegate Porphyria Disease

“…Crystal Structure of R59Q and R59G Mutant-The R59W mutation is by far the most prevalent VP-causing mutation identified, and Ͼ94% of the patients in South Africa carry this mutation (16,17). Biochemical studied showed that the R59W mutation dramatically decreased the catalytic constant of hPPO in vitro (17,21,41,42).…”

“…VP is a type of acute hepaticporphyria (9 -11), which is characterized by an abnormal pattern of porphyrin excretion. VP has been found worldwide (12)(13)(14)(15) and is particularly prevalent in the white population of South Africa (ϳ3 in 1000), especially VP caused by the R59W founder mutation (16,17).…”