If classical epidemiological studies suggest that genetic factors may be important in disease causation then linkage studies and gene-disease association studies may be used to try and determine the genes or genetic variants that are responsible.
Linkage studies usually involve looking at large families where the disease affects individuals in several generations.
The key is to identify a genetic marker that is always inherited by those family members with the disease but not by those who do not have the disease.
Linkage studies usually start by identifying genetic markers, commonly single nucleotide polymorphisms (SNPs), on a section of a chromosome and then narrowing the region down until the gene or gene variant of interest is identified. This technique has been used to identify many disease genes, particularly those that are inherited in a Mendelian fashion.
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