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

Clinical features, polysomnography, and genetics association study of restless legs syndrome in clinic based Chinese patients: A multicenter observational study

STUDY OBJECTIVES

To systemically describe the clinical features, polysomnography (PSG) finding, laboratory tests and single-nucleotide polymorphisms (SNPs) in a clinic based Chinese primary restless legs syndrome (RLS) population.

METHODS

This observational study, conducted from January 2020 to October 2021 across 22 sleep labs in China, recruited 771 patients diagnosed with RLS following the 2014 RLSSG criteria. Clinical data, PSG testing, and laboratory examination and SNPs of patients with RLS were collected. A total of 32 SNPs in 24 loci were replicated using the Asian Screening Array chip, employing data from the Han Chinese Genomes Initiative as controls.

RESULTS

In this study with 771 RLS patients, 645 had primary RLS, and 617 has DNA available for SNP study. Among the 645 primary RLS, 59.7% were women. 33% had a family history of RLS, with stronger familial influence in early-onset cases. Clinical evaluations showed 10.4% had discomfort in body parts other than legs. PSG showed that 57.1% of RLS patients had periodic leg movement index (PLMI) of >5/h and 39.1% had PLMI >15/h, respectively; 73.8% of RLS patients had an Apnea-Hypopnea Index (AHI) > 5/h, and 45.3% had an AHI >15/h. The laboratory examinations revealed serum ferritin levels <75 ng/ml in 31.6%, and transferrin saturation (TSAT) of <45% in 88.7% of RLS patients. Seven new SNPs in 5 genes showed a significant allelic association with Chinese primary RLS, with one previously reported (BTBD9) and four new findings (TOX3, PRMT6, DCDC2C, NOS1).

CONCLUSIONS

Chinese RLS patients has specific characters in many aspects. A high family history with RLS not only indicates strong genetic influence, but also reminds us to consider the familial effect in the epidemiological study. Newly developed sequencing technique with large samples remains to be done.

Putative Animal Models of Restless Legs Syndrome: A Systematic Review and Evaluation of Their Face and Construct Validity

Restless legs syndrome (RLS) is a sensorimotor disorder that severely affects sleep. It is characterized by an urge to move the legs, which is often accompanied by periodic limb movements during sleep. RLS has a high prevalence in the population and is usually a life-long condition. While its origins remain unclear, RLS is initially highly responsive to treatment with dopaminergic agonists that target D2-like receptors, in particular D2 and D3, but the long-term response is often unsatisfactory. Over the years, several putative animal models for RLS have been developed, mainly based on the epidemiological and neurochemical link with iron deficiency, treatment efficacy of D2-like dopaminergic agonists, or genome-wide association studies that identified risk factors in the patient population. Here, we present the first systematic review of putative animal models of RLS, provide information about their face and construct validity, and report their role in deciphering the underlying pathophysiological mechanisms that may cause or contribute to RLS. We propose that identifying the causal links between genetic risk factors, altered organ functions, and changes to molecular pathways in neural circuitry will eventually lead to more effective new treatment options that bypass the side effects of the currently used therapeutics in RLS, especially for long-term therapy.

Restless legs syndrome

Restless legs syndrome (RLS) is a common sensorimotor disorder characterized by an urge to move that appears during rest or is exacerbated by rest, that occurs in the evening or night and that disappears during movement or is improved by movement. Symptoms vary considerably in age at onset, frequency and severity, with severe forms affecting sleep, quality of life and mood. Patients with RLS often display periodic leg movements during sleep or resting wakefulness. RLS is considered to be a complex condition in which predisposing genetic factors, environmental factors and comorbidities contribute to the expression of the disorder. RLS occurs alone or with comorbidities, for example, iron deficiency and kidney disease, but also with cardiovascular diseases, diabetes mellitus and neurological, rheumatological and respiratory disorders. The pathophysiology is still unclear, with the involvement of brain iron deficiency, dysfunction in the dopaminergic and nociceptive systems and altered adenosine and glutamatergic pathways as hypotheses being investigated. RLS is poorly recognized by physicians and it is accordingly often incorrectly diagnosed and managed. Treatment guidelines recommend initiation of therapy with low doses of dopamine agonists or α₂δ ligands in severe forms. Although dopaminergic treatment is initially highly effective, its long-term use can result in a serious worsening of symptoms known as augmentation. Other treatments include opioids and iron preparations.

Association Between CLOCK Gene Variants and Restless Legs Syndrome in Koreans

OBJECTIVE

Previous studies have suggested various causes of restless legs syndrome (RLS), including iron and dopamine concentrations in the brain. Genetic influences have also been reported in many studies. There is also a possibility that circadian clock genes may be involved because symptoms of RLS worsen at night. We investigated whether CLOCK and NPAS2 gene polymorphisms were associated with RLS.

METHODS

A total of 227 patients with RLS and 229 non-RLS matched controls were assessed according to the International Restless Legs Syndrome Study Group diagnostic criteria. Genotyping was performed using reverse transcription polymerase chain reaction and high-resolution melting curve analyses.

RESULTS

Although the genotype distributions of the CLOCK variants (rs1801260 and rs2412646) were not significantly different between patients with RLS and non-RLS controls, the allele frequencies of CLOCK rs1801260 showed marginally significant differences between the two groups (X2 =2.98, p=0.085). Furthermore, there was a significant difference in the distribution of CLOCK haplotypes (rs1801260-rs2412646) between patients with RLS and non-RLS controls (p=0.013). The distributions of allelic, genotypic, and haplotypic variants of NPAS2 (rs2305160 and rs6725296) were not significantly different between the two groups.

CONCLUSION

Our results suggest that CLOCK variants may be associated with decreased susceptibility to RLS.

The prevalence and clinical characteristics of restless legs syndrome in patients with iron deficiency anemia in Korea

STUDY OBJECTIVES

While the prevalence and clinical characteristics of restless legs syndrome (RLS) are known to vary according to ethnicity, a detailed evaluation of this condition among patients with iron deficiency anemia (IDA) has not yet been reported in an Asian population. We investigated the prevalence and clinical characteristics of RLS in patients with IDA in Korea compared with age- and sex-matched patients diagnosed with idiopathic RLS.

METHODS

This prospective single-center study was performed at a regional university hospital. Consecutive patients with IDA were enrolled over a 4-year period. Clinical interviews and laboratory tests were conducted at the first visit. RLS diagnosis was confirmed through face-to-face interviews. We randomly selected patients with idiopathic RLS without comorbid medical disorders from our sleep center dataset as control patients. The clinical characteristics of both groups were compared.

RESULTS

We enrolled 124 patients with IDA. Fifty (40.3%) patients were diagnosed with RLS, with 82% exhibiting severe to very severe symptoms. Patients with IDA and RLS were older and reported more sleep deterioration than patients with IDA without RLS. Patients with IDA and RLS also had a more depressed mood and higher periodic limb movement index scores than patients with idiopathic RLS.

CONCLUSIONS

The prevalence of RLS among patients with IDA in Korea was high, with the majority having severe to very severe symptoms. Patients with IDA and RLS had poorer sleep quality and more emotional problems than patients with IDA without RLS. Therefore, patients with IDA should be screened for RLS to prevent adverse effects on the quality of sleep and life.

Map2k5-Deficient Mice Manifest Phenotypes and Pathological Changes of Dopamine Deficiency in the Central Nervous System

MAP2K5, a member of the MAPK family, is associated with central nervous system disorders. However, neural functional of Map2k5 from animal models were not well examined so far. Here, we established a Map2k5-targeted knockout mouse model to investigate the behavior phenotypes and its underlying molecular mechanism. Our results showed that female Map2k5 mutant mice manifested decreased circadian-dependent ambulatory locomotion, coordination, and fatigue. Male Map2k5 mutant mice displayed impairment in open field exploration and prepulse inhibition of acoustic startle response (ASR) when compared with wild-type controls. Furthermore, Map2k5 mutant mice showed a decreased dopaminergic cell survival and tyrosine hydroxylase levels in nigrostriatal pathway, indicating a crucial role of MAP2K5 in regulating dopamine system in the central nervous system. In conclusion, this is the first study demonstrating that Map2k5 mutant mice displayed phenotypes by disturbing the dopamine system in the central nervous system, implicating Map2k5 mutant mouse as a promising model for many dopamine related disorders.

Ironing out mechanisms of iron homeostasis and disorders of iron deficiency

Iron plays an important role in mammalian physiological processes. It is a critical component for the function of many proteins, including enzymes that require heme and iron-sulfur clusters. However, excess iron is also detrimental because of its ability to catalyze the formation of reactive oxygen species. As a result, cellular and systemic iron levels are tightly regulated to prevent oxidative damage. Iron deficiency can lead to a number of pathological conditions, the most prominent being anemia. Iron deficiency should be corrected to improve adult patients' symptoms and to facilitate normal growth during fetal development and childhood. However, inappropriate use of intravenous iron in chronic conditions, such as cancer and heart failure, in the absence of clear iron deficiency can lead to unwanted side effects. Thus, this form of therapy should be reserved for certain patients who cannot tolerate oral iron and need rapid iron replenishment. Here, we will review cellular and systemic iron homeostasis and will discuss complications of iron deficiency.

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.

Adult Movement Defects Associated with a CORL Mutation in Drosophila Display Behavioral Plasticity

The CORL family of CNS-specific proteins share a Smad-binding region with mammalian SnoN and c-Ski protooncogenes. In this family Drosophila CORL has two mouse and two human relatives. Roles for the mouse and human CORL proteins are largely unknown. Based on genome-wide association studies linking the human CORL proteins Fussel15 and Fussel18 with ataxia, we tested the hypothesis that dCORL mutations will cause adult movement disorders. For our initial tests, we conducted side by side studies of adults with the small deletion Df(4)dCORL and eight control strains. We found that deletion mutants exhibit three types of behavioral plasticity. First, significant climbing defects attributable to loss of dCORL are eliminated by age. Second, significant phototaxis defects due to loss of dCORL are partially ameliorated by age and are not due to faulty photoreceptors. Third, Df(4)dCORL males raised in groups have a lower courtship index than males raised as singles though this defect is not due to loss of dCORL. Subsequent tests showed that the climbing and phototaxis defects were phenocpied by dCORL^21B and dCORL^23C two CRISPR generated mutations. Overall, the finding that adult movement defects due to loss of dCORL are subject to age-dependent plasticity suggests new hypotheses for CORL functions in flies and mammals.

Correlates of Nonanemic Iron Deficiency in Restless Legs Syndrome

Objective: Iron deficiency anemia (IDA) is a well-known cause of secondary restless legs syndrome (RLS). Iron deficiency without anemia (IDNA) is insidious, and its association with RLS is less evaluated. We investigate prevalence and features of IDNA in a consecutive cohort of patients with RLS.

Methods: We included sequential primary RLS patients and RLS patients with IDA. We also recruited age- and gender-matched healthy controls. RLS mimics and other comorbidities were carefully excluded.

Results: One-hundred and ninety-six RLS patients without anemia, 26 RLS patients with IDA, and 63 controls were included. 42.3% of RLS patients without anemia had iron deficiency. Women were much more susceptible for IDNA with a relative risk of 5.51 (p < 0.0001). Women with IDNA and RLS had younger age both at interview and at RLS onset compared to women with RLS without iron deficiency (NID) (P < 0.01). IDNA RLS patients showed a tendency to higher risk of severe/very severe tiredness or sleepiness during the day as compared to NID RLS patients. Furthermore, IDNA RLS patients had longer duration of RLS (P < 0.01 in men, P < 0.05 in women) and younger age at onset (only in men, P < 0.05) compared to IDA RLS patients.

Conclusion: IDNA is frequent in RLS and iron deficiency may be severe despite a normal hemoglobin level. Women are at much higher risk for IDNA, and IDNA in women presents some specific clinical features. Features of IDNA RLS are different from IDA RLS. Regular screening of peripheral iron parameters even in patients with normal blood counts is recommended for timely optimal management.

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.

Caenorhabditis elegans and its applicability to studies on restless legs syndrome

Restless legs syndrome (RLS) is a common neurological disorder in the United States. This disorder is characterized by an irresistible urge to move the legs, although the symptoms vary in a wide range. The pathobiology of RLS has been linked to iron (Fe) deficiency and dopaminergic (DAergic) dysfunction. Several genetic factors have been reported to increase the risk of RLS. Caenorhabditis elegans (C. elegans) is a well-established animal model with a fully sequenced genome, which is highly conserved with mammals. Given the detailed knowledge of its genomic architecture, ease of genetic manipulation and conserved biosynthetic and metabolic pathways, as well as its small size, ease of maintenance, speedy generation time and large brood size, C. elegans provides numerous advantages in studying RLS-associated gene-environment interactions. Here we will review current knowledge about RLS symptoms, pathology and treatments, and discuss the application of C. elegans in RLS study, including the worm homologous genes and methods that could be performed to advance the pathophysiology RLS.

The molecular genetics of human sleep

It has been known for many years that genetic influences account for some of the individual differences in human sleep parameters, but the underlying molecular mechanisms remain unclear. With major advances of molecular biology and the recognition of heritable sleep behaviors in humans over the past 30 years, a number of genetic variants have been identified to be associated with human sleep timing, duration and quality, both in healthy individuals and under pathological conditions. Some of these variants were further validated and characterized in animal models, shedding light on the mechanism of how these variants likely alter sleep in humans, which may provide new insights into developing more effective treatments to improve human sleep.

CORL Expression and Function in Insulin Producing Neurons Reversibly Influences Adult Longevity in Drosophila

CORL proteins (known as SKOR in mice, Fussel in humans and fussel in Flybase) are a family of CNS specific proteins related to Sno/Ski oncogenes. Their developmental and adult roles are largely unknown. A Drosophila CORL (dCORL) reporter gene is expressed in all Drosophila insulin-like peptide 2 (dILP2) neurons of the pars intercerebralis (PI) of the larval and adult brain. The transcription factor Drifter is also expressed in the PI in a subset of dCORL and dILP2 expressing neurons and in several non-dILP2 neurons. dCORL mutant virgin adult brains are missing all dILP2 neurons that do not also express Drifter. This phenotype is also seen when expressing dCORL-RNAi in neurosecretory cells of the PI. dCORL mutant virgin adults of both sexes have a significantly shorter lifespan than their parental strain. This longevity defect is completely reversed by mating (lifespan increases over 50% for males and females). Analyses of dCORL mutant mated adult brains revealed a complete rescue of dILP2 neurons without Drifter. Taken together, the data suggest that dCORL participates in a neural network connecting the insulin signaling pathway, longevity and mating. The conserved sequence and CNS specificity of all CORL proteins imply that this network may be operating in mammals.

CORL Expression in the Drosophila Central Nervous System Is Regulated by Stage Specific Interactions of Intertwined Activators and Repressors

CORL proteins (SKOR in mice and Fussel in humans) are a subfamily of central nervous system (CNS) specific proteins related to Sno/Ski oncogenes. Their developmental and homeostatic roles are largely unknown. We previously showed that Drosophila CORL (dCORL; fussel in Flybase) functions between the Activin receptor Baboon and Ecdysone Receptor-B1 (EcR-B1) activation in mushroom body neurons of third instar larval brains. To better understand dCORL regulation and function we generated a series of reporter genes. We examined the embryonic and larval CNS and found that dCORL is regulated by stage specific interactions between intertwined activators and repressors spanning numerous reporters. The reporter AH.lacZ, which contains sequences 7-11kb upstream of dCORL exon1, reflects dCORL brain expression at all stages. Surprisingly, AH.lacZ was not detected in EcR-B1 expressing mushroom body neurons. In larvae AH.lacZ is coexpressed with Elav and the transcription factor Drifter in dILP2 insulin producing cells of the pars intercerebralis. The presence of dCORL in insulin producing cells suggests that dCORL functions non-autonomously in the regulation of EcR-B1 mushroom body activation via the modulation of insulin signaling. Overall, the high level of sequence conservation seen in all CORL/SKOR/Fussel family members and their common CNS specificity suggest that similarly complex regulation and a potential function in insulin signaling are associated with SKOR/Fussel proteins in mammals.