Restless Legs Syndrome, Susceptibility To, 7

Description

Restless legs syndrome (RLS) is a neurologic sleep/wake disorder characterized by uncomfortable and unpleasant sensations in the legs that appear at rest, usually at night, inducing an irresistible desire to move the legs. The disorder results in nocturnal insomnia and chronic sleep deprivation (Bonati et al., 2003).

For additional information and a discussion of genetic heterogeneity of restless legs syndrome, see RLS1 (102300).

Mapping

In a genomewide association study of 393 patients with restless leg syndrome and 1,602 controls, Winkelmann et al. (2007) found a significant association between restless leg syndrome and rs2300478 in the MEIS1 gene (601739) on chromosome 2p14-p13. The findings were confirmed in 2 independent replication studies of 875 and 211 patients, respectively. Combined results of all 3 studies yielded an overall odds ratio of 1.74 for the G allele (p = 8.08 x 10(-23)). The study also showed evidence for an association with several SNPs within a region on chromosome 15q that contains the LBXCOR1 (611273) and MAP2K5 (602520) genes.

In a study of 244 patients with restless legs syndrome, including 123 familial probands, Vilarino-Guell et al. (2008) confirmed an association with 2 SNPs in the MEIS1 gene. The most significant association was observed for the G allele of rs12469063 (p = 8.2 x 10(-6)) in familial cases.

In a study including 649 RLS patients and 1,230 controls from the Czech Republic, Austria, and Finland, Kemlink et al. (2009) found an association between RLS and rs2300478 in the MEIS1 gene. (p = 1.26 x 10(-5); odds ratio of 1.47). The association was found only in familial and not sporadic cases.

Restless legs syndrome can occur in end-stage renal disease (ESRD), with a prevalence ranging between 18.4 and 45.8% in ESRD patients of European descent (summary by Schormair et al., 2011). In a case-control association study of 200 RLS German patients and 443 non-RLS German patients both with ESRD, Schormair et al. (2011) found an association between RLS and rs12469063 and rs2300478 in the MEIS1 gene: an OR of 1.47-1.52, p (corrected) of 0.013-0.026. However, no association was observed with these SNPs among 141 RLS and 393 non-RLS patients both with ESRD of Greek descent.

Molecular Genetics

Xiong et al. (2009) sequenced all 13 MEIS1 exons and their splice junctions in 285 RLS probands and 285 normal controls and did not identify any causative coding or exon-intron junction mutations. The authors analyzed 2 RLS-associated SNPs, rs12469063 and 2300478, and found a GG/GG risk haplotype (43% vs 25%, p = 0.0095) in 28 RLS and 140 control brain samples. Quantitative real-time PCR analysis detected a significant decrease in MEIS1 expression in lymphoblastoid cell lines (LCLs) and brain tissues from RLS patients with GG/GG risk haplotype compared with RLS patients and controls with the AA/TT nonrisk haplotype. There was significantly decreased MEIS1 protein levels in the same sample of LCLs and brain tissues from GG/GG carriers compared with the AA/TT carriers. Xiong et al. (2009) concluded that reduced expression of the MEIS1 gene, possibly through intronic cis-regulatory elements, predisposes to RLS.

Vilarino-Guell et al. (2009) identified an arg272-to-his (R272H; rs61752693) substitution in the MEIS1 gene in 1 of 71 probands with RLS. The variant segregated with the disorder in 3 additional family members, but was also found in 1 unaffected member. The phenotype in this family was highly variable, with different ages at onset and differing severity. The R272H variant was not found among 378 additional RLS cases or 528 controls from North America, but it was found in 1 of 325 European controls, suggesting reduced penetrance. The substitution was predicted to occur in a highly conserved homeobox 'three-amino acid loop extension' (TALE) domain, but no functional studies were performed. Vilarino-Guell et al. (2009) stated that the pathogenicity of the R272H MEIS1 variant warrants replication.

Schulte et al. (2014) identified synonymous and nonsynonymous rare coding variants in the MEIS1 gene in 9 of 188 German RLS patients compared to 1 of 182 controls, indicating a significant association (p = 0.021). A follow-up study of 3,262 RLS cases of German or Austrian descent and 2,944 controls yielded similar results, with the association becoming stronger as the allele frequency decreased: nonsynonymous MEIS1 alleles with a minor allele frequency (MAF) less than 1% were found in 39 cases compared to 14 controls (p = 0.0024, OR = 2.46), whereas total and nonsynonymous-only alleles with an MAF less than 0.1% were found in 9 cases and 1 control (p = 0.014, OR = 8.14). The association was driven primarily by a low-frequency variant (rs11693221) in the 3-prime UTR of isoform 1 of MEIS1 (OR = 4.42), implicating the UTRs in disease pathogenesis, perhaps through regulating gene expression or mRNA stability. More detailed analysis of the type of variants showed that RLS cases carried an excess of rare variants in the 3- and 5-prime UTRs as well as of nonsynonymous coding variants compared to controls. Functional analysis of selected coding variants was performed in zebrafish using rescue of morpholino knockouts, which showed defects in neurogenesis. Fourteen cases carried 5 variants in isoform 1 of the MEIS1 gene (R203G, S204T, H239Y, R272H, and Q353H) that were shown to be null alleles in zebrafish assays, whereas only 2 controls carried functionally null alleles (Q147K and R272H) (p = 0.0012, OR = 7.48). The findings suggested that reduced activity of MEIS1 isoform 1 contributes to the development of RLS.

Animal Model

Spieler et al. (2014) found that the G risk allele of rs12469063 in the MEIS1 gene alters enhancer function in the developing telencephalon. The G risk allele of rs12469063, located in a highly conserved noncoding region (617), showed decreased reporter gene expression in the neural tube compared to the A protective allele. Decreased enhancer function of the risk allele was also observed in embryonic mouse brain, particularly in the ganglionic eminences, but not in the adult brain. Affinity chromatography identified CREB1 (123810) as an upstream binding factor of rs12469063, binding stronger to the risk allele where it may act as a transcriptional repressor. Adult heterozygous Meis1-deficient mice showed hyperactivity, resembling the RLS phenotype. Spieler et al. (2014) postulated a loss-of-function mechanism that causes a neurodevelopmental defect affecting the basal ganglia with possible age-dependent development of RLS.