Mutation analysis of four genes implicated in iron homeostasis in porphyria cutanea tarda (PCT) patients
Date
2008-03
Authors
Panton, Nicola
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The porphyrias are a group of genetic diseases resulting from the accumulation of haem precursors
due to defective enzyme activity in either one of the last seven enzymes in the haem biosynthesis
pathway. One of the common hepatic porphyrias, porphyria cutanea tarda (PCT), arises from the
inhibition of uroporphyrinogen decarboxylase (UROD) activity. It is characterised by excessive
urinary and hepatic excretion of uroporphyrinogens and manifests cutaneously in the form of
dermatitis. Two main forms of PCT have been described, namely familial PCT (fPCT) and sporadic
PCT (sPCT). PCT is a complex disease and a few genetic (including modifier loci) and
environmental precipitating factors have been implicated in the aetiology of PCT. An important
exacerbating factor, iron overload, is observed in the majority of PCT patients.
The aim of this study was to determine whether DNA sequence variation in the 5' untranslated
regulatory region of four genes involved in iron metabolism i.e. CP, CYBRD1, HAMP and
SLC40A1 may in any way be associated with PCT. The study cohort consisted of 74 patients from
three diverse South African populations including 15 Black (eight males and seven females), 30
Caucasian (13 male and 17 females) and 29 Coloured (18 males and 11 females) individuals as well
as 132 population-matched controls. The promoter region of the selected genes were screened for
variation utilising the techniques of polymerase chain reaction (PCR) amplification, heteroduplex
single-stranded conformational polymorphism (HEX-SCCP) analysis, restriction fragment length
polymorphism (RFLP) analysis and bi-directional semi-automated DNA sequencing.
Twenty three previously described and eleven novel variants were identified. The novel variants
comprised CYBRD1: -1540G/A, -1474G/A, -1452T/C, -1346T/C, -1272T/C, -645T/C;
G(T)8G(T)nG(T)nG(T)9; HAMP: -429G/T and SLC40A1: -1461T/C, -1399G/A, -524C/T.
Statistically significant associations were observed at a number of loci. In silico analysis revealed
several putative transcription factor binding sites (TFBSs) spanning the regions of variation. The
disruption of an existing (or creation of a novel) TFBS is thought to occur in the presence of a variant in a number of instances. This may lead to the manipulation of transcription rates, thereby
depicting a possible mechanism for gene dysregulation.
The study presented here was undertaken as a preliminary investigation to determine the
contribution (if any) of variants in the regulatory regions of candidate genes in iron metabolism in
South African PCT patients. Considering the increasing incidence of PCT, in particular the Black
South African population, it is necessary to elucidate the underlying mechanisms of iron overload in
PCT patients. The propitious findings signified in the study, in conjunction with phenotypegenotype
correlations, will assist in clarifying the association between iron overload and PCT.
Description
Thesis (MSc (Genetics))--University of Stellenbosch, 2008.
Keywords
Porphyria, Iron overload, Mutation screening, Genes, Dissertations -- Genetics, Theses -- Genetics, Porphyria -- Genetic aspects