A step forward for restless legs syndrome

MEIS1 and Restless Legs Syndrome: A Comprehensive Review

Restless legs syndrome (RLS) is a common sleep-related disorder for which the underlying biological pathways and genetic determinants are not well understood. The genetic factors so far identified explain less than 10% of the disease heritability. The first successful genome-wide association study (GWAS) of RLS was reported in 2007. This study identified multiple RLS associated risk variants including some within the non-coding regions of MEIS1. The MEIS1 GWAS signals are some of the strongest genetic associations reported for any common disease. MEIS1 belongs to the homeobox containing transcriptional regulatory network (HOX). Work in C. elegans showed a link between the MEIS1 ortholog and iron homeostasis, which is in line with the fact that central nervous system (CNS) iron insufficiency is thought to be a cause of RLS. Zebrafish and mice have been used to study the MEIS1 gene identifying an RLS-associated-SNP dependent enhancer activity from the highly conserved non-coding regions (HCNR) of MEIS1. Furthermore, this gene shows a lower expression of mRNA and protein in blood and thalamus of individuals with the MEIS1 RLS risk haplotype. Simulating this reduced MEIS1 expression in mouse models resulted in circadian hyperactivity, a phenotype compatible with RLS. While MEIS1 shows a strong association with RLS, the protein's function that is directly linked to an RLS biological pathway remains to be discovered. The links to iron and the enhancer activity of the HCNRs of MEIS1 suggest promising links to RLS pathways, however more in-depth studies on this gene's function are required. One important aspect of MEIS1's role in RLS is the fact that it encodes a homeobox containing transcription factor, which is essential during development. Future studies with more focus on the transcriptional regulatory role of MEIS1 may open novel venues for RLS research.

A direct interaction between two Restless Legs Syndrome predisposing genes: MEIS1 and SKOR1

Restless Legs syndrome (RLS) is a common sleep disorder for which the genetic contribution remains poorly explained. In 2007, the first large scale genome wide association study (GWAS) identified three genomic regions associated with RLS. MEIS1, BTBD9 and MAP2K5/SKOR1 are the only known genes located within these loci and their association with RLS was subsequently confirmed in a number of follow up GWAS. Following this finding, our group reported the MEIS1 risk haplotype to be associated with its decreased expression at the mRNA and protein levels. Here we report the effect of the risk variants of the three other genes strongly associated with RLS. While these variants had no effect on the mRNA levels of the genes harboring them, we find that the homeobox transcription factor MEIS1 positively regulates the expression of the transcription co-repressor SKOR1. This regulation appears mediated through the binding of MEIS1 at two specific sites located in the SKOR1 promoter region and is modified by an RLS associated SNP in the promoter region of the gene. Our findings directly link MEIS1 and SKOR1, two significantly associated genes with RLS and also prioritize SKOR1 over MAP2K5 in the RLS associated intergenic region of MAP2K5/SKOR1 found by GWAS.

Haplotype Association of the MAP2K5 Gene with Antipsychotics-Induced Symptoms of Restless Legs Syndrome among Patients with Schizophrenia

OBJECTIVE

Restless legs syndrome (RLS) is considered a genetic disease and, following a genome-wide association study conducted in 2007, the mitogen-activated protein kinase 5 (MAP2K5) gene has been regarded as the promising candidate gene for RLS. The present study investigated whether polymorphisms of MAP2K5 are associated with antipsychotics-induced RLS in schizophrenia.

METHODS

We assessed antipsychotics-induced RLS symptoms in 190 Korean schizophrenic patients using the diagnostic criteria of the International Restless Legs Syndrome Study Group. Five single-nucleotide polymorphisms (SNPs) of MAP2K5 were genotyped. We investigated genetic and haplotypic associations of these five SNPs with the risk of antipsychotics-induced RLS symptoms.

RESULTS

We divided the 190 subjects into 2 groups: 1) those with RLS symptoms (n=96) and 2) those without RLS symptoms (n=94). There were no significant intergroup differences in the distributions of the genotypes and alleles of the rs1026732, rs11635424, rs12593813, rs4489954, and rs3784709 SNPs. However, the haplotype analysis showed that the G-G-G-G-T (rs1026732-rs11635424-rs12593813-rs4489954-rs3784709) haplotype was associated with RLS symptoms (permutation p=0.033).

CONCLUSION

These data suggest that a haplotype of MAP2K5 polymorphisms confers increased susceptibility to antipsychotics-induced RLS symptoms in schizophrenic patients.

Astrocyte-specific overexpressed gene signatures in response to methamphetamine exposure in vitro

BACKGROUND

Astrocyte activation is one of the earliest findings in the brain of methamphetamine (Meth) abusers. Our goal in this study was to identify the characteristics of the astrocytic acute response to the drug, which may be critical in pathogenic outcomes secondary to the use.

METHODS

We developed an integrated analysis of gene expression data to study the acute gene changes caused by the direct exposure to Meth treatment of astrocytes in vitro, and to better understand how astrocytes respond, what are the early molecular markers associated with this response. We examined the literature in search of similar changes in gene signatures that are found in central nervous system disorders.

RESULTS

We identified overexpressed gene networks represented by genes of an inflammatory and immune nature and that are implicated in neuroactive ligand-receptor interactions. The overexpressed networks are linked to molecules that were highly upregulated in astrocytes by all doses of methamphetamine tested and that could play a role in the central nervous system. The strongest overexpressed signatures were the upregulation of MAP2K5, GPR65, and CXCL5, and the gene networks individually associated with these molecules. Pathway analysis revealed that these networks are involved both in neuroprotection and in neuropathology. We have validated several targets associated to these genes.

CONCLUSIONS

Gene signatures for the astrocytic response to Meth were identified among the upregulated gene pool, using an in vitro system. The identified markers may participate in dysfunctions of the central nervous system but could also provide acute protection to the drug exposure. Further in vivo studies are necessary to establish the role of these gene networks in drug abuse pathogenesis.

Depth and Distribution of Symptoms in Restless Legs Syndrome/ Willis-Ekbom Disease

STUDY OBJECTIVES

To determine the depth and distribution of sensory discomfort in idiopathic restless legs syndrome/Willis-Ekbom disease (RLS) and RLS concurrent with other leg conditions, specifically peripheral neuropathy, sciatica, leg cramps, and arthritis.

METHODS

RLS subjects (n = 122) were divided into 71 idiopathic RLS and 51 RLS-C, or Comorbid, groups. All subjects were examined by an RLS expert, answered standardized RLS questionnaires, and received a body diagram to draw the location and depth of their symptoms.

RESULTS

Age was 63.04 ± 12.84 years, with 77 females and 45 males. All patients had lower limb involvement and 43/122 (35.25%) also had upper limb involvement. Of the 122 subjects, 42.62% felt that the RLS discomfort was only deep, 9.84% felt that the discomfort was only superficial, and 47.54% felt both superficial and deep discomfort. There were no defining characteristics in depth or distribution of RLS sensations that differentiated those patients with idiopathic RLS from those patients with RLS associated with other comorbid leg conditions. The sensation of arthritis was felt almost exclusively in the joints and not in the four quadrants of the leg, whereas the exact opposite was true of RLS sensations.

CONCLUSIONS

Depth and distribution cannot be used as a discriminative mechanism to separate out idiopathic RLS from RLS comorbid with other leg conditions. Although seen in clinical practice, the total absence of patients with non-painful RLS only in the joints in the current study attests to the rarity of this presentation and raises the possibility of misdiagnosis under these circumstances. We recommend that such patients not be admitted to genetic or epidemiological studies.

The Molecular Genetics of Restless Legs Syndrome

Restless legs syndrome (RLS) is a common sensorimotor trait defined by symptoms that interfere with sleep onset and maintenance in a clinically meaningful way. Nonvolitional myoclonus while awake and asleep is a sign of the disorder and an informative endophenotype. The genetic contributions to RLS/periodic leg movements are substantial, are among the most robust defined to date for a common disease, and account for much of the variance in disease expressivity. The disorder is polygenic, as revealed by recent genome-wide association studies. Experimental studies are revealing mechanistic details of how these common variants might influence RLS expressivity.

Association studies of variants in MEIS1, BTBD9, and MAP2K5/SKOR1 with restless legs syndrome in a US population

BACKGROUND

A genome-wide association study (GWAS) identified significant association between variants in MEIS1, BTBD9, and MAP2K5/SKOR1 and restless legs syndrome (RLS). However, many independent replication studies are needed to unequivocally establish a valid genotype-phenotype association across various populations. To further validate the GWAS findings, we investigated three variants, rs2300478 in MEIS1, rs9357271 in BTBD9, and rs1026732 in MAP2K5/SKOR1 in 38 RLS families and 189 RLS patients/560 controls from the US for their association with RLS.

METHOD

Both family-based and population-based case-control association studies were carried out.

RESULTS

The family-based study showed that SNP rs1026732 in MAP2K5/SKOR1 was significantly associated with RLS (P=0.01). Case-control association studies showed significant association between all three variants and RLS (P=0.0001/OR=1.65, P=0.0021/OR=1.59, and P=0.0011/OR=1.55 for rs2300478, rs9357271, and rs1026732, respectively).

CONCLUSION

Variants in MEIS1, BTBD9, and MAP2K5/SKOR1 confer a significant risk of RLS in a US population.

Family-based and population-based association studies validate PTPRD as a risk factor for restless legs syndrome

OBJECTIVE

We previously mapped a genetic locus for restless legs syndrome (RLS) to chromosome 9p22-24 (RLS3) and a later genome-wide association study (GWAS) implicated the PTPRD gene at the RLS3 locus as a susceptibility gene for RLS. However, from the standpoint of genetics, the GWAS association needs to be validated by independent studies. In this study, we used both family-based and population-based association studies to assess the association between PTPRD and RLS in an American Caucasian population.

METHODS

We genotyped two intronic SNPs rs1975197 and rs4626664 in PTPRD in 144 family members from 15 families and a case control cohort of 189 patients and 560 controls. Direct DNA sequence analysis was used to screen coding exons and exon-intron boundaries of PTPRD for rare mutations.

RESULTS

A family-based sibling transmission disequilibrium test showed association of RLS with SNP rs1975197 (P = 0.015), but not with rs4626664 (P = 0.622). The association with rs1975197 was significantly replicated by a population-based case control association study (allelic P = 0.0004, odds ratio = 1.68; genotypic P = 0.0013 and 0.0003 for an additive and dominant model, respectively). One rare p.E1639D variant was identified in exon 39 in kindred RLS40005. The rare D1639 allele did not co-segregate with RLS in the family, suggesting that p.E1639D variant is not a causative mutation.

CONCLUSIONS

This represents the first independent study to validate the association between PTPRD variants and RLS. Both family-based and population-based association studies suggest that PTPRD variant rs1975197 confers risk of RLS.

Advances in the science of genomics in restless legs syndrome

Restless legs syndrome (RLS) is a sleep and movement disorder that affects up to 15% of the population across the lifespan. Many health care providers have doubted its validity as an illness and are uncertain as to the implications of health care outcomes. The cause of RLS is unknown. Common treatment options include dopaminergics, benzodiazepines, and opioids; however, the pharmacogenetic mechanisms of treatment are unknown. One of the greatest genetic discoveries in 2007 was the identification of genetic variance associated with RLS. There is, however, a lack of knowledge related to RLS and its genetic basis. Therefore, the purposes of this article are to (a) provide information about the science of clinical care related to RLS; (b) present a systematic review of the literature on the status of genetics/genomics of RLS, including the discovery of associated genetic variance; and (c) identify implications of the current state of the science for health care providers and biobehavioral researchers. With the continuing genetic discoveries in RLS, health care providers, specifically nurses who play a major role in research, genetic counseling, and education, need to understand the implications of this sleep and movement disorder for patients across the lifespan.

Treating restless legs syndrome with rotigotine

Restless legs syndrome has attracted increasing interest as a clinically significant, common and treatable disorder. Good evidence suggests that dopaminergic drugs are the most effective first-line agents when symptoms are severe.

Restless legs syndrome and painful neuropathy-retrospective study. A role for nociceptive deafferentation?

OBJECTIVES

Restless legs syndrome (RLS) occurs in polyneuropathy with small fiber involvement, possibly as a peculiar form of neuropathic pain; however, the relationship between pain and RLS has been poorly investigated in polyneuropathy.

DESIGN, SETTING, AND PATIENTS

We evaluated retrospectively the occurrence of RLS in 102 consecutive patients with polyneuropathy manifesting with neuropathic pain or dysesthesia, referred to the Neuromuscular Center, using the National Institutes of Health criteria for RLS. The patients were classified in subgroups characterized respectively by allodynia (hyperphenomena), with reported unpleasant sensations evoked by tactile stimuli, and hypoalgesia (hypophenomena), with absent pain sensation to pinprick, according to putative mechanisms of pain.

RESULTS

RLS was present in 41/102 patients (40.2%). It was significantly more frequent in the "hypoalgesia" (23/37) than in the "allodynia" subgroup (9/31; P = 0.008) and in the not classifiable cases (9/34; P = 0.004).

CONCLUSIONS

RLS is frequent in painful polyneuropathy and is significantly associated with decreased small fiber input, thus nociceptive deafferentation may represent a factor interacting with RLS "generators," possibly at spinal level. We suggest that overactivity of the spinal structures implicated in RLS may be triggered by nociceptive deafferentation in a subgroup of patients with painful polyneuropathy. Our findings, prompting a mechanistic characterization of RLS associated with painful polyneuropathy, have to be confirmed in a prospective study.

MEIS1 intronic risk haplotype associated with restless legs syndrome affects its mRNA and protein expression levels

Restless legs syndrome (RLS) is a common neurological disorder characterized by an irresistible urge to move the legs at night, which is often accompanied by unpleasant sensations. A recent genomewide association study identified an association between RLS and intronic markers from the MEIS1 gene. Comparative genomic analysis indicates that MEIS1 is the only gene encompassed in this evolutionarily conserved chromosomal segment, i.e. a conservation synteny block, from mammals to fish. We carried out a series of experiments to delineate the role of MEIS1 in RLS pathogenesis and the underlying genetic mechanism. We sequenced all 13 MEIS1 exons and their splice junctions in 285 RLS probands with confirmed clinical diagnosis and did not identify any causative coding or exon-intron junction mutations. We found no evidence of structural variation or disease-associated haplotype differential splicing. However, sequencing of conserved regions of MEIS1 introns 8 and 9 identified a novel single nucleotide polymorphism (C13B_2) significantly associated with RLS (allelic association, P = 1.81E-07). We detected a significant decrease in MEIS1 mRNA expression by quantitative real-time polymerase chain reaction in lymphoblastoid cell lines (LCLs) and brain tissues from RLS patients homozygous for the intronic RLS risk haplotype, compared with those homozygous for the non-risk haplotype. Finally, we found significantly decreased MEIS1 protein levels in the same batch of LCLs and brain tissues from the homozygous carriers of the risk haplotype, compared with the homozygous non-carriers. Therefore, these data suggest that reduced expression of the MEIS1 gene, possibly through intronic cis-regulatory element(s), predisposes to RLS.

Update of the pathophysiology of the restless-legs-syndrome

The Restless Legs Syndrome (RLS) is a heterogeneous disease. Symptomatic or secondary forms encompass iron deficiency, uremia, pregnancy, polyneuropathy, and other causes. The so-called idiopathic RLS syndrome preferentially affects patients with a younger onset before the age of 30. Here we summarize pathophysiological results along the anatomical route, beginning at the cortex and followed by the basal ganglia, thalamus, A11 neurones, substantia nigra, brainstem nuclei, and spinal cord. Genetic risk variants for RLS have recently been identified in two genes, one of them the homeobox gene MEIS1, known to be involved in embryonic development and variants in a second locus containing the genes encoding mitogen-activated protein kinase MAP2K5, and the transcription factor LBXCOR1. A third one, the BTBD9 gene with unknown function encodes a BTB(POZ) domain. Accordingly, new concepts on pathophysiology have to bridge conventional knowledge with possible consequences deriving from these findings. Furthermore, this may create a framework to help understand why dopamine, opioid, and some anticonvulsant therapies are effective in RLS patients.

From human genetics and genomics to pharmacogenetics and pharmacogenomics: past lessons, future directions

A brief history of human genetics and genomics is provided, comparing recent progress in those fields with that in pharmacogenetics and pharmacogenomics, which are subsets of genetics and genomics, respectively. Sequencing of the entire human genome, the mapping of common haplotypes of single-nucleotide polymorphisms (SNPs), and cost-effective genotyping technologies leading to genome-wide association (GWA) studies - have combined convincingly in the past several years to demonstrate the requirements needed to separate true associations from the plethora of false positives. While research in human genetics has moved from monogenic to oligogenic to complex diseases, its pharmacogenetics branch has followed, usually a few years behind. The continuous discoveries, even today, of new surprises about our genome cause us to question reviews declaring that "personalized medicine is almost here" or that "individualized drug therapy will soon be a reality." As summarized herein, numerous reasons exist to show that an "unequivocal genotype" or even an "unequivocal phenotype" is virtually impossible to achieve in current limited-size studies of human populations. This problem (of insufficiently stringent criteria) leads to a decrease in statistical power and, consequently, equivocal interpretation of most genotype-phenotype association studies. It remains unclear whether personalized medicine or individualized drug therapy will ever be achievable by means of DNA testing alone.