the heritability of hypertension and large vessel atherosclerosis [2] . Genetic research makes use of two main approaches to identify gene variants related to disease: linkage and association studies. Linkage relies on the fact that the recombination of gene sequences is more likely to occur between loci that are further apart on the genome than between loci closer together. Thus, the coinheritance of two distant loci that occurs more often than would be expected by chance indicates linkage of

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... disease to a locus. Linkage analysis in family samples makes it possible to identify distant genetic markers in families that would otherwise be missed in general population samples because the recombination of distant loci occurs only sporadically, and not within a few generations. The polygenic nature of common complex diseases complicates the linkage approach. The second approach is to study the association between allelic variation within specific genes and cerebral ischaemia, for instance, by comparing genotype frequencies in stroke patients and healthy controls. A gene variant that is more common in patients than in controls may cause stroke or be located close to the true causal variant. The use of association studies in complex diseases has become popular as a result of lower power in family studies and advances in high throughput genotyping.