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Isolation of CA dinucleotide repeats close to D6S105; linkage disequilibrium with haemochromatosis
C Stone1, J J Pointon, E C Jazwinska
1MRC Molecular Haematology Unit, Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, UK.
Insights
Hereditary haemochromatosis (HC) is linked to chromosome 6p markers. Fluorescent in situ hybridization shows D6S105 is telomeric to HLA-A, defining a large critical region for HC. Novel microsatellites were developed to improve genetic mapping.
Area of Science:
- Human Genetics
- Molecular Biology
- Medical Research
Background:
- Hereditary haemochromatosis (HC) gene linkage is established to chromosome 6p markers, specifically HLA-A and D6S105.
- Linkage disequilibrium has been observed between these markers and HC, suggesting proximity to the disease gene.
- The precise physical distance and order of HLA-A and D6S105 on chromosome 6p remained uncharacterized.
Purpose of the Study:
- To determine the physical localization of D6S105 relative to HLA-A on chromosome 6p.
- To characterize the size of the hereditary haemochromatosis critical region.
- To identify and develop novel polymorphic markers for enhanced genetic resolution within the HC critical region.
Main Methods:
- Fluorescent in situ hybridization (FISH) was employed to physically map D6S105 in relation to HLA-A.
- Isolation and characterization of novel CA dinucleotide repeat microsatellites near D6S105.
- Linkage disequilibrium analysis using newly developed microsatellites in hereditary haemochromatosis patients and control populations.
Main Results:
- FISH analysis demonstrated that D6S105 is located at least 1-2 Mb telomeric to HLA-A.
- The hereditary haemochromatosis critical region, spanning from proximal HLA-A to distal D6S105, is confirmed to be extensive.
- Three novel CA dinucleotide repeat microsatellites were successfully isolated near D6S105.
- Linkage disequilibrium studies involving two of these microsatellites provided evidence supporting D6S105 as a close marker to the HC gene.
Conclusions:
- The physical mapping confirms a significant distance between HLA-A and D6S105, indicating a large critical region for hereditary haemochromatosis.
- The development of novel, highly polymorphic microsatellite markers is crucial for improving genetic resolution and fine-mapping the HC gene.
- The findings support the utility of D6S105 and potentially the novel microsatellites for future genetic studies and marker-assisted diagnosis of hereditary haemochromatosis.
Abstract:
The gene for hereditary haemochromatosis (HC) is linked to HLA-A and D6S105 on chromosome 6p. Both markers have also been reported to display linkage disequilibrium with the disease. However, their physical localization relative to one another has not been established. We demonstrate by fluorescent in situ hybridisation that D6S105 lies at least 1-2 Mb telomeric of HLA-A. The haemochromatosis critical region extending from proximal of HLA-A to distal of D6S105 is therefore large. To improve the genetic resolution in this region more highly polymorphic markers are required. We have therefore isolated three novel CA dinucleotide repeats close to D6S105. A linkage disequilibrium study, with two of these microsatellites, in HC patients and controls lends support to the conclusion that D6S105 is a close marker to the haemochromatosis gene.