Haemochromatosis is the most common single gene disorder to afflict North- West European populations. It is probably the most common genetic disorder of iron metabolism worldwide. As many as 1 in 250 people in the UK are affected and although the phenotype causes only a mild increase in gastrointestinal iron absorption a proportion of affected individuals will accumulate sufficient iron over their life-time to cause cirrhosis and hepatocellular carcinoma. Venesection treatment instituted before cirrhosis has established ensures a normal life expectancy, but clinical presentation is often late in life after irreversible organ injury has occurred. Identification of people at risk in the early, asymptomatic stage by measurements of iron status is unreliable. The genetic defect responsible for haemochromatosis has been sought in the hope that its identification might facilitate early diagnosis and that studies on the gene product would lead to a greater understanding of the mechanisms of mammalian iron absorption. Genetic linkage to HLA-A3 placed the gene responsible for haemchromatosis in, or close to, the major histocompatibilty complex (MHC) on the short arm of chromosome 6 and a positional cloning strategy has been adopted. This thesis describes work directed to the identification of the haemochromatosis gene by positional cloning. The region telomeric to the MHC was mapped using yeast artificial chromosomes, from which new microsatellites were isolated. These markers were used in linkage disequilibrium analyses and the mapping of a recombination breakpoint that defined a haemochromatosis gene region. This region was physically mapped in fine detail and positional candidates sought by EST database analysis. Before a systematic search for genes in the region began a strong positional candidate was reported (Feder et al 1996). Analysis of this mutation in patients from the UK confirmed this to be the ancestral haemochromatosis mutation.

[Truncated abstract. Please see the pdf format for the complete text.] The discovery of the C282Y mutation and its role in the development of hereditary haemochromatosis has allowed a greater understanding into the effects of iron overload and its involvement in other conditions such as diabetes and heart disease. It has also allowed the better classification of heterozygotes, who were previously only diagnosed through the use of family studies. There are however, areas of conflict between phenotyping and genotyping methods. My research involved examining the relationship between Haemochromatosis and certain diseases such as diabetes and heart disease; genotyping versus phenotyping discrepancies and the possible interaction of secondary mutations. In Chapter 3 a population study was undertaken with the aim of comparing genotyping versus phenotyping methods as well as increasing general practitioner awareness regarding hereditary haemochromatosis and its diagnosis. It was determined that a minimum of 5000 subjects would be required to give the study sufficient power. Individuals were to be between the ages of 20—40 years, and thus presumably presymptomatic. Participation was entirely voluntary and a consent form was to be signed. Recruitment of subjects proved to be difficult and there was a selective bias towards individuals already displaying symptoms of haemochromatosis. In total less than a 100 subjects were recruited for the study. There were several issues encountered in the implementation of this study. Firstly the number of GPs participating was probably insufficient to recruit the subjects required. A more extensive campaign was probably required to enroll more GPs. Secondly it is very difficult for a busy GP to find the time necessary to explain the study to each of his patients and to get them to sign the consent form. Finally a bias developed in some of the requests. The subjects participating in this study were supposed to be random but in many cases the GPs had enrolled them in the study because they had symptoms of iron overload. In effect the biggest obstacle this study faced was the recruitment of subjects. Due to the small number of subjects little statistical data could be obtained from this study. It was noted, however, that genotyping methods detected two individuals who were homozygous for the C282Y mutation. Both also had increased transferrin saturation levels. Phenotyping detected 5 individuals with increased transferrin saturation. The three others detected via phenotyping were C282Y heterozygotes. Haemochromatosis has long been though to be related to the development of diabetes due to the effect of iron overload on the pancreas. If this is so it would be logical to assume that the prevalence of haemochromatosis would be higher in a diabetic population. Chapter 4 examined the possibility that diabetics have a higher frequency of the C282Y mutation. A population group consisting of 1355 diabetics was genotyped for the C282Y mutation and iron studies were performed on all heterozygotes and C282Y homozygotes. Initial findings indicated that there was a significant difference between the diabetic and control population. However, this finding was the opposite of what was expected, there seemed to be a decreased frequency of the Y allele in the diabetic population rather than an increased one. The control and diabetic populations were not matched in terms of ethnicity. The removal of the ethnic bias in the diabetic population altered the statistics so there was no longer a significant difference between the two groups. This study highlighted the importance of using appropriate control populations as comparison groups. The final results of the study indicated that there was no significant difference between the diabetic population and the control population. This would seem to indicate that there is not an increased occurrence of the C282Y mutation in the diabetic population when compared to the control group. Chapter 5 considered the possible association between C282Y heterozygosity and cardiovascular disease as well as the potential for early mortality. Several recent studies have indicated that C282Y heterozygosity may be a risk factor for the development of atherosclerosis, possibly on the basis of increased iron loading. Using a control population and a population of individuals with known coronary events the incidence of the C282Y mutation was compared against other risk factors. C282Y heterozygosity did not appear to be a risk factor for atherosclerosis. There was however, a statistically significant link between increased ferritin in women and carotid plaques. A population of elderly women was genotyped in order to examine the effects of C282Y heterozygosity on longevity. The first hypothesis addressed in chapter 5 was that C282Y heterozygosity was a risk factor for the development of coronary heart disease.

Thesis (MSc)--University of Stellenbosch, 2008. / ENGLISH ABSTRACT: Iron metabolism disorders comprise the most common disorders in humans. Hereditary haemochromatosis (HH) is a common condition resulting from inappropriate iron absorption. The most common form of the disease (Type 1) is associated with mutations in the HFE gene. The C282Y homozygous genotype accounts for approximately 80% of all reported cases of HH within the Caucasian population. A second HFE mutation, H63D, is associated with less severe disease expression. The C282Y mutation is extremely rare in Asian and African populations. The H63D mutation is more prevalent and has been observed in almost all populations. Iron overload resulting from haemochromatosis is predicted to be rare in Asian Indian populations and is not associated with common HFE mutations that are responsible for HH in the Caucasian population. The aberrant genes associated with HH in India have not yet been identified. The present study attempted to identify variants in six iron regulatory genes that were resulting in the Type 1 HH phenotype observed in two Asian Indian probands from a highly consanguineous family. The promoter and coding regions of the HMOX1, HFE, HAMP, SLC40A1, CYBRD1 and HJV genes were subjected to mutation analysis. Gene fragments were amplified employing the polymerase chain reaction (PCR) and subsequently subjected to heteroduplex single-strand conformational polymorphism (HEX-SSCP) analysis. Samples displaying aberrations were then analysed using bi-directional semi-automated DNA sequencing analysis to identify any known or novel variants within the six genes. Variants disrupting restriction enzyme recognition sites were genotyped employing restriction fragment length polymorphism (RFLP) analysis. Mutation analysis of the six genes revealed 24 previously identified variants, five novel variants (HFE: 5’UTR-840T→G, CYBRD1: 5’UTR-1813C→T, 5’UTR-1452T→C, 5’UTR- 1272T→C; HJV: 5’UTR-534G→T, 5’UTR-530G→T), one previously described microsatellite and two novel repeats. Variants identified within the SLC40A1, CYBRD1 and HJV genes do not seem to be associated with the iron overload phenotype. A previously described HAMP variant (5’UTR-335G→T) was observed in the homozygous state in both probands. This variant seems to be the genetic aberration responsible for iron overload in this Indian family. The severe juvenile haemochromatosis phenotype usually associated with HAMP mutations, was not exhibited by the two Indian probands. Their symptoms resembled those observed in classic Type 1 HH. It is suggested that variants identified in the HMOX1 and HFE genes are modifying the effect of the HAMP variant and resulting in the less severe disease phenotype. Although this variant has only been identified in one Indian family, it could shed some light in the hunt for the iron-loading gene in India. / AFRIKAANSE OPSOMMING: Oorerflike hemochromatose (OH) is ‘n algemene siektetoestand wat ontstaan as gevolg van oneffektiewe opname van yster in die liggaam. Die mees algemene vorm van die siekte (Tipe 1) word geassosieer met mutasies in die HFE-geen. Die C282Y homosigotiese genotipe is verantwoordelik vir ongeveer 80% van alle gerapporteerde gevalle van OH binne die Kaukasiese bevolking. ‘n Tweede HFE mutasie, H63D, word geassosieer met minder ernstige siekte simptome. Die C282Y mutasie is besonder skaars in Asiese en Afrika bevolkings. Daar word bespiegel dat oorerflike ysteroorlading as gevolg van hemochromatose skaars is in Asiese Indiër bevolkings en word nie geassosieer met algemene HFE mutasies wat verantwoordelik is vir OH in Kaukasiese bevolkings nie. Die abnormale gene wat wél geassosieer word met OH in Indië is tot dusver nog nie identifiseer nie. Die doel van hierdie studie was om die variante in ses yster-regulerende gene te identifiseer wat die Tipe 1 OH fenotipe in hierdie familie veroorsaak. Hierdie fenotipe is waargeneem in twee Asies Indiese familielede afkomstig van ‘n bloedverwante familie. Die promotor en koderingsareas van die HMOX1, HFE, HAMP, SLC40A1, CYBRD1 en HJV gene is gesif vir mutasies. Geen fragmente is geamplifiseer met behulp van die polimerase kettingsreaksie (PKR) en daarna aan heterodupleks enkelstring konformasie polimorfisme (HEX-SSCP) analise blootgestel. PKR produkte wat variasies getoon het, is daarna geanaliseer deur tweerigting semi-geoutomatiseerde DNS volgorde-bepalingsanalise om enige bekende of nuwe variante binne die ses gene te identifiseer. Variante waar restriksie ensiem herkenningsetels teenwoordig is, is verder analiseer met behulp van die restriksie fragment lengte polimorfisme (RFLP) analise sisteem. Mutasie analise van die ses gene het 24 bekende variante, vyf nuwe variante (HFE: 5’UTR- 840T→G, CYBRD1: 5’UTR-1813C→T, 5’UTR-1452T→C, 5’UTR-1272T→C, HJV: 5’UTR-534G→T, 5’UTR-530G→T), een bekende herhaling en twee nuwe herhalings gewys. Variante wat binne die SLC4041, CYBRD1 en HJV gene geïdentifiseer is, blyk nie om by te dra tot die ysteroorladings-fenotipe nie. Die bekende HAMP variant (5’UTR-335G→T) is waargeneem in die homosigotiese toestand in beide van die aangetaste individue. Hierdie variant blyk om die genetiese fout te wees wat verantwoordelik is vir die ysteroorlading in die betrokke Indiese familie. Die erge juvenielehemochromatose fenotipe wat meestal geassosieer word met HAMP-mutasies, is nie waargeneem in hierdie familie nie. Hul simptome kom ooreen met die simptome van die klassieke Tipe 1 OH. Dit blyk moontlik te wees dat die variante identifiseer in die HMOX1 en HFE gene die impak van die HAMP variant modifiseer en die matiger siekte-fenotipe tot gevolg het. Alhoewel hierdie variant slegs in een Indiese familie geïdentifiseer is, kan dit lig werp op die soektog na die veroorsakende ysterladingsgeen in Indië.