Analysis of the NRAMP1 gene implicated in iron transport: association with multiple sclerosis and age effects.

Multiple sclerosis (MS) is believed to be an autoimmune process occurring in genetically susceptible individuals after an appropriate environmental exposure. We have exploited the homogeneous Afrikaner population of European ancestry to investigate the likelihood that iron dysregulation, in association with infectious and/or autoimmune disease susceptibility, may underlie the MS phenotype in a subgroup of patients. The functional Z-DNA forming repeat polymorphism of the natural resistance-associated macrophage protein-1 (NRAMP1) gene was analyzed in 104 patients diagnosed with MS and 522 Caucasian controls. A family-based control group consisting of 32 parental alleles not transmitted to MS offspring was additionally studied to exclude the likelihood of population substructures. Statistically significant differences in allelic distribution were observed between the patient and control samples drawn from the same population (P < 0.01). Evidence is furthermore provided that alleles considered to be detrimental in relation to autoimmune disease susceptibility may be maintained in the population as a consequence of improved survival to reproductive age following infectious disease challenge. Although it remains to be determined whether the disease phenotype in MS patients with allele 5 of the NRAMP1 promoter polymorphism is directly related to dysregulation of iron or modified susceptibility to viral infection and/or autoimmunity, a combination of these processes most likely underlies the disease phenotype in these patients. In view of the emerging role of polymorphic variants in complex diseases and minimizing of possible confounding factors in this association study, we conclude that allelic variation in the NRAMP1 promoter may contribute significantly to MS susceptibility in the South African Caucasian population.

Molecular analysis reveals a high mutation frequency in the first untranslated exon of the PPOX gene and largely excludes variegate porphyria in a subset of clinically affected Afrikaner families.

A subset of probands from 11 South African families with clinical and/or biochemical features of variegate porphyria (VP), but without the known protoporphyrinogen oxidase (PPOX) gene defects identified previously in the South African population, were subjected to mutation analysis. Disease-related mutation(s) could not be identified after screening virtually the entire PPOX gene by heteroduplex single-strand conformation polymorphism analysis (HEX-SSCP), although three new sequence variants were detected in exon 1 of the gene in three normal controls. The presence of these single base changes at nucleotide positions 22 (C/G), 27 (C/A) and 127 (C/A), in addition to the known exon 1 polymorphisms I-26 and I-150, indicates that this untranslated region of the PPOX gene is particularly mutation-prone. Furthermore, microsatellite markers flanking the PPOX and alpha-1 antitrypsin (PI) gene, on chromosomes 1 and 14, respectively, were used to assess the probability of involvement of these loci in disease presentation. Common alleles transmitted from affected parent to affected child were determined where possible in the mutation-negative index cases. Allelic frequencies of these <> alleles were compared to findings in the normal population, but no predominant disease-associated allele could be identified. Co-segregation of a specific haplotype with the disease phenotype could also not be demonstrated in a large Afrikaner family. It is concluded that further studies are warranted to determine the genetic factor(s) underlying the autosomal dominant pattern of inheritance in molecularly uncharacterized cases showing clinical symptoms of an acute porphyria.