A Genetic Risk Factor for Periodic Limb Movements in Sleep

To the Editor: Stefansson et al. (Aug. 16 issue) 1 report the results of a genomewide association study of the restless legs syndrome (RLS) in an Icelandic series. The analysis revealed that one single-nucleotide polymorphism (SNP) in the BTB (POZ) domain–containing 9 ( BTBD9 ) gene was associated with RLS. Replication in smaller samples from Iceland and the United States showed that the discovery originated from a subgroup of patients with RLS who presented with periodic limb movements in sleep, a common feature of RLS. Winkelmann et al. 2 performed a similar analysis for patients with RLS who were of European descent, . . .