Association Between Vitamin D Receptor rs731236 (Taq1) Polymorphism and Risk for Restless Legs Syndrome in the Spanish Caucasian Population

Vitamin D receptor and binding protein genes variants in patients with migraine

BACKGROUND/OBJECTIVES

Several studies have shown a relationship between vitamin D and migraine, including the association between decreased serum 25-hydroxyvitamin D in patients with migraine and the positive effects of vitamin D supplementations in the therapy of this disease. Two single-nucleotide variants (SNVs) vitamin D receptor (VDR) gene, VDR rs2228570, and VDR rs731236 have shown an association with migraine risk in a previous case-control association study, while an exome sequencing study identified a rare variant in GC vitamin D binding protein gene. This study aims to look for the association between several common variants in these two genes and the risk for migraine.

METHODS

We genotyped 290 patients diagnosed with migraine and 300 age-matched controls using specific TaqMan assays for VDR rs2228570, VDR rs731236, VDR rs7975232, VDR rs739837, VDR rs78783628, GC rs7041, and GC rs4588 SNVs.

RESULTS

We did not find an association between these SNVs and the risk for migraine. None of these SNVs were related to the positivity of a family history of migraine or with the presence of aura. The VDR rs731236A allele showed a significant association with the triggering of migraine attacks by ethanol (Pc = 0.007).

CONCLUSIONS

In summary, the results of the current study suggest a lack of association between common SNVs in the VDR and GC gene and the risk of developing migraine. The possible relationship between VDR rs731236 and the triggering of migraine episodes with ethanol deserves future studies.

LAG3/CD4 Genes Variants and the Risk for Restless Legs Syndrome

According to several studies, inflammatory factors could be related to the pathogenesis of idiopathic restless legs syndrome (RLS). In addition, RLS and Parkinson's disease (PD) have shown a possible relationship, and recent studies have shown an association between CD4 rs1922452 and CD4 rs951818 single nucleotide variants (SNVs) and the risk for PD. For these reasons, we investigated the possible association between common variants in the LAG3/CD4 genes (which encoded proteins involved in inflammatory and autoimmune responses) and the risk for RLS in a Caucasian Spanish population. We assessed the frequencies of CD4 rs1922452, CD4 rs951818, and LAG3 rs870849 genotypes and allelic variants in 285 patients with idiopathic RLS and 350 healthy controls using a specific TaqMan-based qPCR assay. We also analyzed the possible influence of the genotypes' frequencies on several variables, including age at onset of RLS, gender, family history of RLS, and response to drugs commonly used in the treatment of RLS. We found a lack of association between the frequencies of genotypes and allelic variants of the 3 SNVs studied and the risk of RLS, and a weak though significant association between the CD4 rs1922452 GG genotype and an older age at onset of RLS. With the exception of this association, our findings suggest that common SNVs in the CD4/LAG3 genes are not associated with the risk of developing idiopathic RLS in Caucasian Spanish people.

Reassessment of candidate gene studies for idiopathic restless legs syndrome in a large genome-wide association study dataset of European ancestry

Study Objectives

Several candidate gene studies have been published for idiopathic restless legs syndrome (RLS) in populations of European ancestry, but the reported associations have not been confirmed in independent samples. Our aim was to reassess these findings in a large case–control dataset in order to evaluate their validity.

Methods

We screened PubMed for RLS candidate gene studies. We used the genome-wide association study (GWAS) dataset of the International EU-RLS-GENE Consortium as our replication sample, which provided genome-wide single-variant association data based on at most 17 220 individuals of European ancestry. We performed additional gene-based tests using the software MAGMA and assessed the power of our study using the genpwr R package.

Results

We identified 14 studies conducted in European samples which assessed 45 variants in 27 genes of which 5 variants had been reported as significantly associated. None of these individual variants were replicated in our GWAS-based reassessment (nominal p > 0.05) and gene-based tests for the respective five genes ADH1B, GABRR3, HMOX1, MAOA, and VDR, were also nonsignificant (nominal p > 0.05). Our replication dataset was well powered to detect the reported effects, even when adjusting for effect size overestimation due to winner’s curse. Power estimates were close to 100% for all variants.

Conclusion

In summary, none of the significant single-variant associations from candidate gene studies were confirmed in our GWAS dataset. Therefore, these associations were likely false positive. Our observations emphasize the need for large sample sizes and stringent significance thresholds in future association studies for RLS.

Vitamin D Receptor and Binding Protein Gene Variants in Patients with Essential Tremor

Several studies have shown an association between some variants in the vitamin D receptor (VDR) and the GC vitamin D binding protein (GC) genes with the risk for Parkinson's disease or other neurological disorders. VDR rs2228570 has shown an association with essential tremor (ET) in a previous study. The aim of this study is to look for the association between several common variants in these genes and the risk for ET. We genotyped 272 patients diagnosed with familial ET and 272 age-matched controls using specific TaqMan assays for VDR rs2228570, VDR rs731236, VDR rs7975232, VDR rs739837, VDR rs78783628, GC rs7041, and GC rs4588 single nucleotide variants (SNVs). We found an association between GC rs7041 SNV and ET using recessive, codominant, and allelic models. Despite our results did not find an association between VDR rs2228570 and ET, the pooled data with those by a previous report suggest this association under recessive, codominant, and allelic models. None of the SNVs studied was related to the age at onset of tremor in ET patients. Data from the current study suggest an association between GC rs7041 and VDR rs2228570 SNVs and ET risk.

Natural selection at work? Vitamin D deficiency rates and rising health problems in young Turkish Cypriot professionals

OBJECTIVES

Vitamin D is a fat-soluble, prohormone vitamin that is important especially for bone mineralization and skeletal health. In recent years, vitamin D deficiency appeared as a worldwide problem, affecting many people in different ways including the Northern Cypriot population. The deficiency might be caused by the lack of exposure to sunlight, diet low in vitamin D, sedentary lifestyle, and also due to some genetic variations in the vitamin D receptor (VDR) gene.

METHODS

In this study, four common VDR polymorphisms and associations with vitamin D deficiency in the Turkish Cypriot population between ages 18-40 and working in office conditions was studied by PCR- RFLP analysis.

RESULTS

rs2228570 C>T variant was shown to be significantly associated with low serum vitamin D levels in the studied population.

CONCLUSION

Together with the effect of rs2228570 C>T variant in the VDR gene, it is thought that the lifestyle changes in the Turkish Cypriot population might have caused the increased frequency of vitamin D deficiency in the young professionals.

Common Endothelial Nitric Oxide Synthase Single Nucleotide Polymorphisms are not Related With the Risk for Restless Legs Syndrome

Because nitric oxide and endothelial dysfunction could play a role in the pathogenesis of idiopathic restless legs syndrome (RLS), as was suggested by some preliminary data, we investigated the possible association between the rs2070744 variants in the endothelial nitric oxide synthase (eNOS or NOS3) gene (chromosome 7q36.1) and the risk for RLS in a Caucasian Spanish population. We assessed the frequencies of NOS3 single nucleotide polymorphisms (SNPs) rs2070744, rs1799983, and rs79467411 genotypes and allelic variants in 273 patients with idiopathic RLS and 325 healthy controls using a TaqMan-based qPCR assay. We also analyzed the possible influence of genotype frequency on age at onset of RLS symptoms, gender, family history of RLS, and response to drugs commonly used in the treatment of RLS such as dopaminergic drugs, clonazepam, and GABAergic drugs. The frequencies of genotypes and allelic variants were not associated with the risk for RLS and were not influenced by gender, age, and positive family history of RLS. We identified weak statistical associations of the SNP rs1799983 with the response to dopamine agonists (Pc = 0.018 for the rs1799983 G/T genotype) and of the SNP rs79467411 with the response to clonazepam (Pc = 0.018 for the rs79467411 G allele), although these findings should be cautiously interpreted and require further confirmation. These associations aside, our findings suggest that common NOS3 SNPs are not associated with the risk for idiopathic RLS in Caucasian Spanish people.

Searching for Novel Candidate Biomarkers of RLS in Blood by Proteomic Analysis

PURPOSE

We performed comparative proteomic analyses of blood of patients with RLS and healthy individuals aiming to identify potential biomarker and therapeutic target candidate for RLS.

PATIENTS AND METHODS

Blood serum samples from 12 patients with a clinical diagnosis of RLS (8 females and 4 males, with a mean age of 68.52 years) and 10 healthy controls (5 females and 5 males, with a mean age of 67.61 years) underwent proteomic profiling by liquid chromatography coupled with tandem mass spectrometry. Pathway analysis incorporating protein-protein interaction networks was carried out to identify pathological processes linked to the differentially expressed proteins.

RESULTS

We quantified 272 proteins in patients with RLS and healthy controls, of which 243 were shared. Five proteins - apolipoprotein C-II, leucine-rich alpha-2-glycoprotein 1, FLJ92374, extracellular matrix protein 1, and FLJ93143 - were substantially increased in RLS patients, whereas nine proteins - vitamin D-binding protein, FLJ78071, alpha-1-antitrypsin, CD5 antigen-like, haptoglobin, fibrinogen alpha chain, complement factor H-related protein 1, platelet factor 4, and plasma protease C1 inhibitor - were decreased. Bioinformatics analyses revealed that these proteins were linked to 1) inflammatory and immune response, and complement activation, 2) brain-related development, cell aging, and memory disorders, 3) pregnancy and associated complications, 4) myocardial infarction, and 5) reactive oxygen species generation and subsequent diabetes mellitus.

CONCLUSION

Our findings shed light on the multifactorial nature of RLS and identified a set of circulating proteins that may have clinical importance as biomarkers and therapeutic targets.

Serum vitamin D, vitamin D receptor and binding protein genes polymorphisms in restless legs syndrome

BACKGROUND/OBJECTIVES

Several studies showed lower serum 25-hydroxyvitamin D levels in patients with idiopathic restless legs syndrome (RLS) compared with matched controls, and a single study showed an association between the rs731236 single nucleotide polymorphism (SNP) in the vitamin D receptor (VDR) gene and the risk for RLS. We aimed to study the relationship between the serum 25-hydroxyvitamin D levels and to confirm previous findings related to SNPs in the VDR and the GC vitamin D binding protein (GC) gene, with the risk for RLS in the Spanish Caucasian population.

METHODS

We genotyped 285 idiopathic RLS patients and 325 age and sex-matched controls for VDRrs2228750, VDRrs7975232, VDRrs739837, VDRrs78783628, GCrs7041 and GCrs4588 SNPs using TaqMan assays, and determined serum 25-hydroxyvitamin D levels in 111 idiopathic RLS patients and 167 controls using an ELISA commercial kit.

RESULTS

Serum 25-hydroxyvitamin D levels were significantly higher in RLS patients than in controls but were unrelated with the 7 SNPs studied. None of the 7 SNPs analyzed was associated with the risk for idiopathic RLS or with a positive family history of RLS. However, RLS patients carrying the rs7975232CC genotype or the rs7975232C allele, had a higher frequency of response to GABAergic drugs. Associations between the age at onset and the severity of RLS with SNPs were inconsistent.

CONCLUSIONS

This study shows an association between increased serum concentrations of 25-hydroxyvitamin D and a lack of association between 7 SNPs in the VDR and in the GC genes with RLS in the Spanish Caucasian population.

Unraveling the Mysteries of Restless Leg Syndrome

Restless leg syndrome (RLS) or Willis-Ekbom disease (WED) is an under-diagnosed, chronic, and progressive primary sensory-motor disorder. It is characterized by an uncontrollable urge to move the legs due to uncomfortable and sometimes painful sensations, with a diurnal variation. RLS can lead to severe sleep disturbances, a usual cause of consultation. The pathophysiology is known partially, and it is believed that there is an association between the different variants of genetic mutations combined with dopaminergic and brain iron dysregulation, which plays an important role. The data used for this study were extracted from the articles found in the PubMed database that discuss different gene variants, pathophysiology, and various methods of treatment. They also highlight the role of iron in the pathogenesis of RLS as it is required for the synthesis of tyrosine hydroxylase, which is the rate-limiting step for dopamine synthesis. This review article provides a clinically useful overview of RLS in terms of pathophysiological findings, its genetic associations, and therapeutic options by using the currently available literature. Because RLS presents with vague symptoms and shares similarities with many other diseases, it might be overlooked by many physicians resulting in underdiagnosis and under-treatment. While these discoveries provide a breakthrough in understanding the details of RLS, further studies are recommended as these studies are limited to animal models and provide a limited representation of the general population.

Mineral absorption is an enriched pathway in a brain region of restless legs syndrome patients with reduced MEIS1 expression

Restless legs syndrome is a common complex disorder with different genetic and environmental risk factors. Here we used human cell lines to conduct an RNA-Seq study and observed how the gene showing the most significant association with RLS, MEIS1, acts as a regulator of the expression of many other genes. Some of the genes affected by its expression level are linked to pathways previously reported to be associated with RLS. We found that in cells where MEIS1 expression was either increased or prevented, mineral absorption is the principal dysregulated pathway. The mineral absorption pathway genes, HMOX1 and VDR are involved in iron metabolism and response to vitamin D, respectively. This shows a strong functional link to the known RLS pathways. We observed the same enrichment of the mineral absorption pathway in postmortem brain tissues of RLS patients showing a reduced expression of MEIS1. The expression of genes encoding metallothioneins (MTs) was observed to be dysregulated across the RNA-Seq datasets generated from both human cells and tissues. MTs are highly relevant to RLS as they bind intracellular metals, protect against oxidative stress and interact with ferritins which manage iron level in the central nervous system. Overall, our study suggests that in a subset of RLS patients, the contribution of MEIS1 appears to be associated to its downstream regulation of genes that are more directly involved in pathways that are relevant to RLS. While MTs have been implicated in the pathogenesis of neurodegenerative diseases such as Parkinson’s diseases, this is a first report to propose that they have a role in RLS.

IL1B polymorphism is associated with essential tremor in Chinese population

BACKGROUND

The aim of the study was to investigate the genetic risk factors of essential tremor (ET) in Chinese Population.

METHODS

A total of 225 ET patients (25 ET patients also had restless legs syndrome (RLS) and were excluded from final analysis) and 229 controls were recruited. The diagnosis of ET was based on the Consensus Statement of the Movement Disorders Society on tremor. Polymerase chain reaction (PCR) and sequencing were used to detect 12 single nucleotide polymorphisms (SNPs) in seven candidate genes for RLS (HMOX1, HMOX2, VDR, IL17A, IL1B, NOS1 and ADH1B).

RESULTS

We found that one SNP was associated with the risk of ET in Chinese population after adjusting for age and gender: rs1143633 of IL1B (odds ratio [OR] =2.57, p = 0.003, recessive model), and the statistical result remained significant after Bonferroni correction. Then, we performed a query in Genotype-tissue Expression (GTEx), Brain eQTL Almanac (Braineac) databases and Blood expression quantitative trait loci (eQTL) browser. The significant association was only found between genotype at rs1143633 and IL1B expression level of putamen and white matter in Braineac database, which was more prominent with homozygous (GG) carriers.

CONCLUSIONS

Our study firstly reported the association of IL1B polymorphism with the risk of ET in Chinese population. However, the association might only suggest a marker of IL1B SNP associated with ET instead of the casual variant. Further studies are needed to confirm our finding.

Association Between the rs1229984 Polymorphism in the Alcohol Dehydrogenase 1B Gene and Risk for Restless Legs Syndrome

Background/Objectives

Several studies have raised the possibility of an association between alcohol consumption and the risk of developing restless legs syndrome (RLS). Moreover, an important percentage of patients under alcohol detoxification therapy develop RLS symptoms that fulfil the criteria for idiopathic RLS during alcohol withdrawal. We have aimed to establish the possible association between two common single nucleotide polymorphisms (SNPs) in the alcohol-dehydrogenase 1B (ADH1B) gene and the risk for RLS.

Methods

We studied, using specific TaqMan assays, the genotype and allelic variant frequencies of ADH1B rs1229984 and ADH1B rs6413413 SNPs in 205 RLS patients and 505 gender-matched healthy controls.

Results

The sum of the frequencies of rs1229984CT and rs1229984TT genotypes, as well as the frequency of the rs1229984T allelic variant, was significantly higher in RLS patients than in controls, both in the whole group and in females. The frequencies of genotypes and allelic variants of the rs6413413 SNP were similar between the two groups. RLS patients with the rs1229984CT genotype were younger, and those with the rs122984TT genotype older, at onset of RLS symptoms than those with the rs1229984CC genotype. None of the studied SNPs were related either with positivity of family history for RLS or with RLS severity.

Conclusions

These results suggest an association between rs1229984 SNP and the risk for RLS.

Association of BTBD9 and MAP2K5/SKOR1 With Restless Legs Syndrome in Chinese Population

Study Objectives

The aim of the study was to investigate the relationship between genetic factors and primary restless legs syndrome (RLS) in Chinese population.

Methods

A total of 116 RLS patients and 200 controls were recruited and the diagnosis of RLS was based on the criteria of International RLS Study Group. Polymer chain reaction (PCR) and sequencing were used to detect 19 single nucleotide polymorphisms (SNPs) in six genetic loci (MEIS1, BTBD9, PTPRD, MAP2K5/SKOR1, TOX3, and Intergenic region of 2p14).

Results

Our study found that one SNP increased the risk of RLS in Chinese population: rs6494696 of MAP2K5/SKOR1 (odds ratio [OR] = 0.09, p < .0001, recessive model). A further meta-analysis of RLS in Asian population found that two SNPs of BTBD9 increased the risk of RLS: rs9296249 of BTBD9 (OR = 1.44, p = .000, T allele), rs9357271 of BTBD9 (OR = 1.38, p = .021, dominant model).

Conclusion

Our results confirmed the association of BTBD9 and MAP2K5/SKOR1 with primary RLS in Chinese population.

Restless Legs Syndrome: From Pathophysiology to Clinical Diagnosis and Management

Restless legs syndrome (RLS), a common neurological sensorimotor disorder in western countries, has gained more and more attention in Asian countries. The prevalence of RLS is higher in older people and females. RLS is most commonly related to iron deficiency, pregnancy and uremia. The RLS symptoms show a significant circadian rhythm and a close relationship to periodic limb movements (PLMs) in clinical observations, while the pathophysiological pathways are still unknown. The diagnostic criteria have been revised in 2012 to improve the validity of RLS diagnosis. Recent studies have suggested an important role of iron decrease of brain in RLS pathophysiology. Dopaminergic (DA) system dysfunction in A11 cell groups has been recognized long ago from clinical treatment and autopsy. Nowadays, it is believed that iron dysfunction can affect DA system from different pathways and opioids have a protective effect on DA system. Several susceptible single nucleotide polymorphisms such as BTBD9 and MEIS1, which are thought to be involved in embryonic neuronal development, have been reported to be associated with RLS. Several pharmacological and non-pharmacological treatment are discussed in this review. First-line treatments of RLS include DA agents and α2δ agonists. Augmentation is very common in long-term treatment of RLS which makes prevention and management of augmentation very important for RLS patients. A combination of different types of medication is effective in preventing and treating augmentation. The knowledge on RLS is still limited, the pathophysiology and better management of RLS remain to be discovered.