Genetics of restless legs syndrome.

At the outset of genetic studies in restless legs syndrome (RLS), the disorder was assumed to be a classical monogenic disorder that runs in families. However, years of family studies did not reveal any causally-related genes or genetic variants. The advent of high-throughput genotyping technology led to a change; genome-wide association studies in large case-control samples became feasible, which led to the identification of first genetic risk variants for RLS. Variants detected by this approach are common ones, which that individually confer only a minor increase in risk of disease. Overall, the currently known risk variants in six genomic loci account for only a small proportion of the genetically determined susceptibility to RLS. Additional risk loci and individual variants remain to be discovered. First studies indicate that rare genetic variants are also important contributors in RLS. These are expected to have a larger impact on the phenotype and may thus prove to be excellent candidates for functional studies and, in the long-term, targets for developing therapeutics or preventive measures. To enable their discovery, large-scale studies including tens of thousands of affected individuals may be needed. Next-generation sequencing technologies such as whole exome or whole genome sequencing will be essential for this endeavor. Even though the number of known risk variants is still limited, they have been indispensable in terms of deciphering the underlying pathophysiology of RLS, providing the molecular starting points for animal models and in vitro studies to understand disease mechanisms. In addition, genetic risk variants can be valuable tools for disentangling the phenotypic complexity observed in RLS. Testing RLS risk variants for associations with periodic limb movements (PLMs) identified a significant role of some of the variants and suggested PLMs as an endophenotype in RLS. Further advances in genetics research in RLS will be driven by large-scale sequencing projects and the identification of additional common, but also rarer risk variants with larger effects on disease risk. Another uncharted territory in RLS research epigenetic effect on gene activity. Overall, genetic studies continue to hold great potential for understanding biology of the disease.