Evidence for a genetic association between monoamine oxidase A and restless legs syndrome

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.

Identification of potential blood biomarkers associated with suicide in major depressive disorder

Suicides have increased to over 48,000 deaths yearly in the United States. Major depressive disorder (MDD) is the most common diagnosis among suicides, and identifying those at the highest risk for suicide is a pressing challenge. The objective of this study is to identify changes in gene expression associated with suicide in brain and blood for the development of biomarkers for suicide. Blood and brain were available for 45 subjects (53 blood samples and 69 dorsolateral prefrontal cortex (DLPFC) samples in total). Samples were collected from MDD patients who died by suicide (MDD-S), MDDs who died by other means (MDD-NS) and non-psychiatric controls. We analyzed gene expression using RNA and the NanoString platform. In blood, we identified 14 genes which significantly differentiated MDD-S versus MDD-NS. The top six genes differentially expressed in blood were: PER3, MTPAP, SLC25A26, CD19, SOX9, and GAR1. Additionally, four genes showed significant changes in brain and blood between MDD-S and MDD-NS; SOX9 was decreased and PER3 was increased in MDD-S in both tissues, while CD19 and TERF1 were increased in blood but decreased in DLPFC. To our knowledge, this is the first study to analyze matched blood and brain samples in a well-defined population of MDDs demonstrating significant differences in gene expression associated with completed suicide. Our results strongly suggest that blood gene expression is highly informative to understand molecular changes in suicide. Developing a suicide biomarker signature in blood could help health care professionals to identify subjects at high risk for suicide.

Epigenetic Modifications in Stress Response Genes Associated With Childhood Trauma

Adverse childhood experiences (ACEs) may be referred to by other terms (e.g., early life adversity or stress and childhood trauma) and have a lifelong impact on mental and physical health. For example, childhood trauma has been associated with posttraumatic stress disorder (PTSD), anxiety, depression, bipolar disorder, diabetes, and cardiovascular disease. The heritability of ACE-related phenotypes such as PTSD, depression, and resilience is low to moderate, and, moreover, is very variable for a given phenotype, which implies that gene by environment interactions (such as through epigenetic modifications) may be involved in the onset of these phenotypes. Currently, there is increasing interest in the investigation of epigenetic contributions to ACE-induced differential health outcomes. Although there are a number of studies in this field, there are still research gaps. In this review, the basic concepts of epigenetic modifications (such as methylation) and the function of the hypothalamic-pituitary-adrenal (HPA) axis in the stress response are outlined. Examples of specific genes undergoing methylation in association with ACE-induced differential health outcomes are provided. Limitations in this field, e.g., uncertain clinical diagnosis, conceptual inconsistencies, and technical drawbacks, are reviewed, with suggestions for advances using new technologies and novel research directions. We thereby provide a platform on which the field of ACE-induced phenotypes in mental health may build.

Sleep disorders and Parkinson disease; lessons from genetics

Parkinson disease is a common, age-related neurodegenerative disorder, projected to afflict millions of individuals in the near future. Understanding its etiology and identifying clinical, genetic or biological markers for Parkinson disease onset and progression is therefore of major importance. Various sleep-related disorders are the most common group of non-motor symptoms in advanced Parkinson disease, but they can also occur during its prodromal phase. However, with the exception of REM sleep behavior disorder, it is unclear whether they are part of the early pathological process of Parkinson disease, or if they develop as Parkinson disease advances because of treatments and neurodegeneration progression. The advancements in genetic studies in the past two decades have generated a wealth of information, and recent genetic studies offer new insight on the association of sleep-related disorders with Parkinson disease. More specifically, comparing genetic data between Parkinson disease and sleep-related disorders can clarify their association, which may assist in determining whether they can serve as clinical markers for Parkinson disease risk or progression. In this review, we discuss the current knowledge on the genetics of sleep-related disorders in Parkinson disease context, and the potential implications on research, diagnosis, counseling and treatment.

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.

Sleep disturbance as detected by actigraphy in pre-pubertal juvenile monkeys receiving therapeutic doses of fluoxetine

Sleep disturbance is a reported side effect of antidepressant drugs in children. Using a nonhuman primate model of childhood selective serotonin reuptake inhibitor (SSRI) therapy, sleep was studied quantitatively with actigraphy. Two 48-h sessions were recorded in the home cage environment of juvenile male rhesus monkeys at two and three years of age, after one and two years of treatment with a therapeutic dose of the SSRI fluoxetine, and compared to vehicle treated controls. A third session was conducted one year after discontinuation of treatment at four years of age. During treatment, the fluoxetine group demonstrated sleep fragmentation as indexed by a greater number of rest-activity transitions compared to controls. In addition fluoxetine led to more inactivity during the day as indexed by longer duration of rest periods and the reduced activity during these periods. The fluoxetine effect on sleep fragmentation, but not on daytime rest, was modified by the monkey's genotype for polymorphisms of monoamine oxidase A (MAOA), an enzyme that metabolizes serotonin. After treatment, the fluoxetine effect on nighttime rest-activity transitions persisted, but daytime activity was not affected. The demonstration in this nonhuman primate model of sleep disturbance in connection with fluoxetine treatment and specific genetic polymorphisms, and in the absence of diagnosed psychopathology, can help inform use of this drug in children.

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 between restless legs syndrome and CLOCK and NPAS2 gene polymorphisms in schizophrenia

Previous studies have suggested that there is a genetic basis to restless legs syndrome (RLS) development. Occurrence of antipsychotic-induced RLS could also be due to differences in genetic susceptibility. We investigated whether CLOCK and NPAS2 gene polymorphisms are associated with RLS in schizophrenic patients on antipsychotics because RLS symptoms usually manifest during the evening and night. We assessed symptoms of RLS in 190 Korean schizophrenic patients on antipsychotics and divided the subjects into two groups according to the International Restless Legs Syndrome Study Group diagnostic criteria: (i) subjects who met all the criteria and (ii) the remaining subjects who did not meet all the criteria. We found a significant difference in the number of subjects with different genotype and allele carrier frequencies for the CLOCK gene (rs2412646) between the two groups (p = 0.031 and 0.010, respectively). Distribution of CLOCK haplotypes (rs2412646-rs1801260) was significantly different between schizophrenic patients with and without RLS (p = 0.021). However, the distributions of allelic, genotypic, and haplotypic variants of NPAS2 (rs2305160 and rs6725296) were not significantly different between the two groups. Our results suggest that CLOCK polymorphisms are associated with increased susceptibility of schizophrenic patients to RLS. We hypothesize that RLS in schizophrenia patients treated with antipsychotics may be a very mild akathisia that manifests during the night and is under control of circadian oscillation.

Monoamine oxidase A gene polymorphism and the pathogenesis of sudden infant death syndrome

OBJECTIVES

To test the hypothesis that there is a significant association between functionally relevant allelic variants of the monoamine oxidase A (MAO-A) polymorphism and sudden infant death syndrome (SIDS).

STUDY DESIGN

In a case-control study of 142 cases of SIDS and 280 sex-matched control cases, the distribution of allelic and genotype variants of a promoter polymorphism of the MAO-A gene was examined using polymerase chain reaction locus amplification and fluorescence based fragment length analysis.

RESULTS

There was a significantly differential distribution of allelic and genotype variants between females with SIDS and controls. Moreover, there was a significant association between SIDS in females and allelic and genotype variants, each related to a higher transcriptional activity at the MAO-A locus.

CONCLUSIONS

Our results suggest a role of MAO-A in female SIDS pathogenesis exerted by functionally relevant allelic and genotype variants of the MAO-A polymorphism. However, with the complex and inconsistent evidence available to date, the impact of the MAO-A promoter polymorphism on SIDS etiology remains unclear.

Association study between antipsychotic-induced restless legs syndrome and polymorphisms of monoamine oxidase genes in schizophrenia

OBJECTIVE

This study aimed to investigate whether the monoamine oxidase (MAO) A and B genes are associated with antipsychotic-induced restless legs syndrome (RLS) in schizophrenia.

METHODS

We assessed antipsychotic-induced RLS symptoms in 190 Korean schizophrenic patients and divided the subjects into two groups: those with RLS symptoms (n = 96) and those without RLS symptoms (n = 94). Genotyping was performed for the variable number of tandem repeat (VNTR) polymorphism of the MAOA gene and A644G polymorphism of the MAOB gene.

RESULTS

There was no significant difference in the genotype and allele frequencies of all polymorphisms investigated between these two groups. However, the result of global haplotype analysis showed a significant difference in haplotype frequencies between male subjects with and without RLS symptoms (p = 0.013). The interaction between two polymorphisms had a significant effect on the RLS scores of both male (p = 0.047) and female (p = 0.028) patients.

CONCLUSIONS

These data do not suggest that the MAOA gene VNTR and MAOB gene A644G polymorphisms are associated with antipsychotic-induced RLS symptoms in schizophrenia. However, we found that the haplotype frequencies differed between the male schizophrenic patients with and without RLS symptom and the interaction between the two polymorphisms had a significant influence on the RLS scores of patients with schizophrenia.

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.

Whole genome association studies in complex diseases: where do we stand?

Hundreds of genome-wide association studies have been performed in recent years in order to try to identify common variants that associate with complex disease. These have met with varying success. Some of the strongest effects of common variants have been found in lateonset diseases and in drug response. The major histocompatibility complex has also shown very strong association with a variety of disorders. Although there have been some notable success stories in neuropsychiatric genetics, on the whole, common variation has explained little of the high heritability of these traits. In contrast, early studies of rare copy number variants have led rapidly to a number of genes and loci that strongly associate with neuropsychiatric disorders. It is likely that the use of whole-genome sequencing to extend the study of rare variation in neuropsychiatry will greatly advance our understanding of neuropsychiatric genetics.

Genotyping sleep disorders patients

OBJECTIVE

The genetic susceptibility factors underlying sleep disorders might help us predict prognoses and responses to treatment. Several candidate polymorphisms for sleep disorders have been proposed, but there has as yet inadequate replication or validation that the candidates may be useful in the clinical setting.

METHODS

To assess the validity of several candidate associations, we obtained saliva deoxyribonucleic acid (DNA) samples and clinical information from 360 consenting research participants who were undergoing clinical polysomnograms. Ten single nucleotide polymorphisms (SNPs) were genotyped. These were thought to be related to depression, circadian sleep disorders, sleep apnea, restless legs syndrome (RLS), excessive sleepiness, or to slow waves in sleep.

RESULTS

With multivariate generalized linear models, the association of TEF rs738499 with depressive symptoms was confirmed. Equivocal statistical evidence of association of rs1801260 (the C3111T SNP in the CLOCK gene) with morningness/eveningness and an association of Apolipoprotein E (APOE) rs429358 with the Epworth Sleepiness Scale (ESS) were obtained, but these associations were not strong enough to be of clinical value by themselves. Predicted association of SNPs with sleep apnea, RLS, and slow wave sleep were not confirmed.

CONCLUSION

The SNPs tested would not, by themselves, be of use for clinical genotyping in a sleep clinic.

No significance of the COMT val158met polymorphism in restless legs syndrome

The catechol-O-methyltransferase (COMT) val(158)met polymorphism, which codes for the substitution of valine (val) by methionine (met) leading to a reduced COMT activity in homo- or heterozygous individuals, is associated with individual pain sensitivity and dopaminergic responses in Parkinson's disease as well as with various chronic painful diseases. Recent investigations support the notion of an alteration of the medial pain pathway as well as of the descending inhibitory control system in restless legs syndrome (RLS), that both involve dopaminergic transmission as well. Thus, the distribution of the COMT val(158)met polymorphism was assessed in 298 RLS patients and compared with 135 healthy controls in relation to sex, age of onset and family history. The data revealed no significant differences in the distribution of the COMT val(158)met polymorphism in RLS patients compared with the control group, also when the heterozygous and the homozygous group containing the (158)met allele were combined. In addition, sex, age of onset and family history were not associated with the COMT val(158)met polymorphism in this German population of RLS patients. The present study adds to previous mostly negative investigations on the genetic determination of dopaminergic transmission in RLS, which have - so far - only detected an association of the MAO-A activity and RLS in females in a French-Canadian population. Further investigations assessing the different COMT haplotypes and experimental and clinical parameters are nevertheless warranted.

The genetics of sleep disorders in humans: narcolepsy, restless legs syndrome, and obstructive sleep apnea syndrome

Sleep disorders are a group of neurological disorders known to cause public health problems associated with interference with daily activities including cognitive problems, poor job performance and reduced productivity. There is strong evidence emerging for the presence of genes influencing sleep disorders, such as narcolepsy (NRCLP), restless legs syndrome (RLS), and obstructive sleep apnea syndrome (OSAS). NRCLP is typically characterized by excessive daytime sleepiness, cataplexy, sleep paralysis and hallucinations. RLS is manifested by compelling need to move the legs and usually experienced when trying to sleep. OSAS is major sleep problem characterized by recurrent episodes of upper airway collapse and obstruction during sleep. In the recent years, many research groups have attempted to identify the susceptibility and candidate genes for NRCLP, RLS, and OSAS through the sequential analyses of genetic linkage and association. The purpose of this review is to summarize some of remarkable molecular advances in sleep and sleep disorders, thereby providing a greater understanding of the complex sleep processes, and a platform for future therapeutic interventions.

Association between Antipsychotics-Induced Restless Legs Syndrome and Tyrosine Hydroxylase Gene Polymorphism

OBJECTIVE

Restless legs syndrome (RLS) has been reported to be more prevalent in schizophrenic patients who take antipsychotics. The cause of RLS is unknown but associated with dopaminergic deficiency. Tyrosine hydroxylase (TH) is the enzyme responsible for catalyzing the conversion of L-tyrosine to DOPA. The purpose of this study is to determine whether the TH gene Val81Met polymorphism is associated with antipsychotic-induced RLS.

METHODS

One hundred ninety Korean schizophrenic patients were evaluated by the diagnostic criteria of the International RLS Study Group (IRLSSG). The genotyping was performed by PCR-based methods.

RESULTS

Of the one hundred ninety schizophrenic patients, 44 (23.2%) were found to have RLS. Although there were no significant associations between TH genotypes or allele frequencies and RLS, when separate analyses were performed by sex (male or female), we detected significant differences in the frequencies of the genotype (chi(2)=6.15, p=0.046) and allele (chi(2)=4.67, p=0.031) of the TH gene Val81Met polymorphism between those with and without RLS in the female patients.

CONCLUSION

These findings suggest that the TH gene Val81Met SNP might be associated with antipsychotic-induced RLS in female schizophrenic patients.

Association between monoamine oxidase A (MAOA) and personality traits in Japanese individuals

It has been reported that personality traits are related to several neurotransmitters. However, the association between personality traits and the central nervous system remains unclear. In the present study, we investigated the relationships between a polymorphism involving a variable number of tandem repeats in the promoter of the monoamine oxidase A (MAOA-VNTR) gene and personality traits, as assessed by the Temperament and Character Inventory (TCI). Promoter VNTRs in the MAOA were genotyped in 558 healthy Japanese individuals. Females homozygous for high-activity allele (4/4) had significantly higher persistence scores than those homozygous for the low-activity allele (3/3) (p=0.012, ANOVA). Meanwhile no difference in persistence was found between 3 and 4 allele in males. There were no differences between other scores of TCI subscales and MAOA-VNTR polymorphism. Our results suggest a gender-specific contribution of MAOA-VNTR polymorphism to persistence scores.

Genetics of restless legs syndrome

Restless legs syndrome (RLS) is a highly familial trait with heritability estimates of about 50%. It is a polygenetic disorder in which a number of variants contribute to the phenotype. Linkage studies in families with RLS revealed several loci but have not yet led to the identification of disease-causing sequence variants. Phenocopies, nonpenetrance, and possible intrafamilial heterogeneity make it difficult to define the exact candidate region. Genome-wide association studies identified variants within intronic or intergenic regions of MEIS1, BTBD9, and MAP2K5/LBOXCOR1. Carriers of one risk allele had a 50% increased risk of developing RLS. MEIS1 and LBXCOR1 are developmental factors and raise new pathophysiologic questions for RLS. These variants have weak and moderate effects and increase the risk of developing RLS. It is still possible that strong effects explain the occurrence of RLS in families. Therefore, linkage and association studies should be used congruently to dissect the complete genetic architecture of RLS.

Restless legs syndrome in type 2 diabetes: implications to diabetes educators

PURPOSE

The purpose of this study was to provide a background of restless legs syndrome (RLS), present the prevalence and demographic findings of a descriptive study of type 2 diabetes with RLS, and provide implications to diabetes educators on the management and education of RLS.

METHODS

Participants with type 2 diabetes who met the diagnostic criteria for RLS based on the International RLS Study Group Criteria were recruited from the PENN Rodebaugh Diabetes Center from July 2005 through September 2006. Participants who met inclusion and exclusion criteria were mailed a survey to collect data.

RESULTS

Of 121 patients with type 2 diabetes, 54 (45%) of the screened sample met the 4 diagnostic criteria for RLS. Of those who met the inclusion and exclusion criteria of the primary study, 18 patients with type 2 diabetes with RLS participated in this study. Along with diabetes, the participants had a variety of comorbid health conditions including hypertension, neuropathies, rheumatoid arthritis, renal failure, and irritable bowel syndrome. Only one third of the participants were being treated for RLS. Thirty-nine percent of the participants with type 2 diabetes were using insulin to manage their diabetes with other oral agents.

CONCLUSIONS

RLS is a sleep disorder that may affect the management of type 2 diabetes. Diabetes educators must know that sleep disorders can affect long-term health outcomes, and RLS is frequently seen in this cohort of patients.

[Restless-legs syndrome]

Restless-legs syndrome (RLS) is a sensorimotor disorder, characterized by an irresistible urge to move the legs usually accompanied or caused by uncomfortable and unpleasant sensations. It begins or worsens during periods of rest or inactivity, is partially or totally relieved by movements and is exacerbated or occurs at night and in the evening. RLS sufferers represent 2 to 3% of the general population in Western countries. Supportive criteria include a family history, the presence of periodic-leg movements (PLM) when awake or asleep and a positive response to dopaminergic treatment. The RLS phenotypes include an early onset form, usually idiopathic with a familial history and a late onset form, usually secondary to peripheral neuropathy. Recently, an atypical RLS phenotype without PLM and l-DOPA resistant has been characterized. RLS can occur in childhood and should be distinguished from attention deficit/hyperactivity disorder, growing pains and sleep complaints in childhood. RLS should be included in the diagnosis of all patients consulting for sleep complaints or discomfort in the lower limbs. It should be differentiated from akathisia, that is, an urge to move the whole body without uncomfortable sensations. Polysomnographic studies and the suggested immobilization test can detect PLM. Furthermore, an l-DOPA challenge has recently been validated to support the diagnosis of RLS. RLS may cause severe-sleep disturbances, poor quality of life, depressive and anxious symptoms and may be a risk factor for cardiovascular disease. In most cases, RLS is idiopathic. It may also be secondary to iron deficiency, end-stage renal disease, pregnancy, peripheral neuropathy and drugs, such as antipsychotics and antidepressants. The small-fiber neuropathy can mimic RLS or even trigger it. RLS is associated with many neurological and sleep disorders including Parkinson's disease, but does not predispose to these diseases. The pathophysiology of RLS includes an altered brain-iron metabolism, a dopaminergic dysfunction, a probable role of pain control systems and a genetic susceptibility with nine loci and three polymorphisms in genes serving developmental functions. RLS treatment begins with the elimination of triggering factors and iron supplementation when deficient. Mild or intermittent RLS is usually treated with low doses of l-DOPA or codeine; the first-line treatment for moderate to severe RLS is dopaminergic agonists (pramipexole, ropinirole, rotigotine). In severe, refractory or neuropathy-associated RLS, antiepileptic (gabapentin, pregabalin) or opioid (oxycodone, tramadol) drugs can be used.

Obesity is Associated with Genetic Variants That Alter Dopamine Availability

Human and animal studies have implicated dopamine in appetite regulation, and family studies have shown that BMI has a strong genetic component. Dopamine availability is controlled largely by three enzymes: COMT, MAOA and MAOB, and by the dopamine transporter SLC6A3, and each gene has a well-characterized functional variant. Here we look at these four functional polymorphisms together, to investigate how heritable variation in dopamine levels influences the risk of obesity in a cohort of 1150, including 240 defined as obese (BMI > or = 30). The COMT and SLC6A3 polymorphisms showed no association with either weight, BMI or obesity risk. We found, however, that both MAOA and MAOB show an excess of the low-activity genotypes in obese individuals (MAOA:chi2= 15.45, p = 0.004; MAOB:chi2= 8.05, p = 0.018). Additionally, the MAOA genotype was significantly associated with both weight (p = 0.0005) and BMI (p = 0.001). When considered together, the 'at risk genotype'--low activity genotypes at both the MAOA and MAOB loci--shows a relative risk for obesity of 5.01. These results have not been replicated and, given the experience of complex trait genetics, warrant caution in interpretation. In implicating both the MAOA and MOAB variants, however, this study provides the first indication that dopamine availability (as opposed to other effects of MAOA) is involved in human obesity. It is therefore a priority to assess the associations in replication datasets.

Genetics of restless legs syndrome (RLS): State-of-the-art and future directions

Several studies demonstrated that 60% of restless legs syndrome (RLS) patients have a positive family history and it has been suggested that RLS is a highly hereditary trait. To date, several loci have been mapped but no gene has been identified yet. Phenocopies and possible nonpenetrants made it difficult to detect a common segregating haplotype within the families. Defining the exact candidate region is hampered by possible intrafamilial, allelic, and nonallelic heterogeneity. One important prerequisite for future successful genetic studies in RLS is the availability of large and thoroughly phenotyped patients and family samples for linkage as well as association studies.

Possible association between G-protein β3 subunit C825T polymorphism and antipsychotic-induced restless legs syndrome in schizophrenia

OBJECTIVE

The incidence of restless legs syndrome (RLS) is presumed to be higher among people with schizophrenia who take antipsychotic medication, most of which blocks the dopamine D2 receptor. The purpose of this study was to determine whether the G-protein β3 subunit (GNB3) C825T polymorphism is associated with antipsychotic-induced RLS in schizophrenia.

METHODS

We examined 178 Korean patients with schizophrenia. All of the subjects were evaluated using the diagnostic criteria of the International Restless Legs Syndrome Study Group and the International Restless Legs Scale. Genotyping was performed for the C825T polymorphism in the GNB3 gene.

RESULTS

The genotype distribution did not differ significantly between antipsychotic-induced RLS patients and patients who had no-RLS symptoms (χ 2 = 4.30, p = 0.116). The genotypes of the C825T single-nucleotide polymorphism (SNP) were classified into two groups: C+ (CC and CT genotypes) and C- (TT genotype). The presence of the C allele (C+) was associated with an increased likelihood of RLS (χ 2 = 4.14, p = 0.042; odds ratio = 2.56, 95% confidence interval = 1.02-6.47).

CONCLUSIONS

These results suggest that the GNB3 C825T SNP is associated with RLS in schizophrenia. However, confirming this association requires future larger scale studies in which the effects of medication are strictly controlled.

A promoter polymorphism in the monoamine oxidase A gene is associated with the pineal MAOA activity in Alzheimer's disease patients

BACKGROUND

Monoamine oxidase A (MAOA) is involved in the pathogenesis of mood disorders and Alzheimer's disease (AD). MAOA activity and gene expression have been found to be up-regulated in different brain areas of AD patients, including the pineal gland. Increased pineal MAOA activity might contribute to the reduced pineal melatonin production in AD. A promoter polymorphism of a variable number tandem repeats (VNTR) in the MAOA gene shows to affect MAOA transcriptional activity in vitro.

METHODS

Here we examined in 63 aged controls and 44 AD patients the effects of the MAOA-VNTR on MAOA gene expression and activity in the pineal gland as endophenotypes, and on melatonin production.

RESULTS

AD patients carrying long MAOA-VNTR genotype (consisting of 3.5- or 4-repeat alleles) showed higher MAOA gene expression and activity than the short-genotyped (i.e., 3-repeat allele) AD patients. Moreover, the AD-related up-regulation of MAOA showed up only among long-genotype bearing subjects. There was no significant effect of the MAOA-VNTR on MAOA activity or gene expression in controls, or on melatonin production in both controls and AD patients.

CONCLUSION

Our data suggest that the MAOA-VNTR affects the activity and gene expression of MAOA in the brain of AD patients, and is involved in the changes of monoamine metabolism.

Age-at-onset in restless legs syndrome: a clinical and polysomnographic study

OBJECTIVE

To determine the distribution of age-at-onset in a large cohort of patients with restless legs syndrome (RLS) and to compare clinical and polysomnographic characteristics of patients with early and late age-at-onset of RLS.

METHODS

Two hundred and fifty patients with RLS were studied. Information on age-at-onset, etiology, familial history and symptoms severity of RLS was obtained. Age-at-onset density functions were determined from bootstrap methods and kernel density estimators.

RESULTS

Age-at-onset showed a significant bimodal distribution with a large peak occurring at 20 years of age and a smaller peak in the mid-40s. Early- and late-onset RLS could be separated with a cut-off at 36 years of age. Distributions of age-at-onset differed as a function of presence/absence of a familial history and etiology of RLS. Age-at-onset clearly differentiated patients with a primary RLS (early onset) from those with secondary RLS. Finally, early-onset RLS was associated with increased RLS severity with higher indices of periodic leg movements in sleep (PLMS) associated with microarousals and periodic leg movements during wakefulness (PLMW).

CONCLUSIONS

Early- and late-onset RLS could be distinguished depending on familial history and etiology of RLS. Our data suggest that different pathological processes are involved in these two groups, the early-onset group being highly genetically determined.

Genetic aspects of restless legs syndrome

Restless legs syndrome (RLS), also known as Ekbom syndrome, is a common movement disorder with sensorimotor symptoms occurring during sleep and quiet wakefulness. The underlying cause for RLS is unknown but genetic influences play a strong part in the pathogenesis of RLS, particularly when the condition starts at a young age. This review explores the genetic basis of RLS and related phenotypic variations. Recently, three loci showing vulnerability to RLS have been described in French-Canadian and Italian families in chromosomes 12q, 14q and 9q, emphasising on an autosomal dominant mode of inheritance. These have been labelled RLS1, RLS2 and RLS3, respectively. However, specific causative mutations remain elusive and no linkage analysis has been identified so far in the candidate genes investigated in RLS.

The biopsychosocial effects of restless legs syndrome (RLS)

The symptoms of restless legs syndrome (RLS) are associated with reductions in patients' quality of life (QoL) and mental heath. Sleep disturbance, which is often the most troublesome symptom of RLS, may have a negative impact on patients' daytime cognitive abilities. Research has established a relationship between the symptoms of RLS and mood symptoms, but causality is unclear. Some studies have indicated that the symptoms of RLS precede those of depression or anxiety, and others relate the severity of mood symptoms to the severity of RLS symptoms. Associations between the sleep disturbance produced by RLS and patients' mood symptoms have also been demonstrated. The impact of RLS symptoms and their treatment on QoL, mental health, and cognition are reviewed herein.

Genetics of the sleep-wake cycle and its disorders

The sleep-wake cycle is under the control of the circadian clock. Recent advances in rhythm biology have identified molecular clocks and their key regulating genes. Circadian clock genes (Clock, Per) were first isolated in Drosophila, and their homologous counterparts have been found in mammals. Some of the circadian master genes have been shown to influence sleeping behavior. For instance, a point mutation in a human clock gene (Per2) was shown to produce the rare advanced sleep phase syndrome, whereas a functional polymorphism in Per3 is associated with the more frequent delayed sleep phase syndrome. Furthermore, a study examining the association between Clock gene polymorphisms and insomnia revealed a higher recurrence of initial, middle, and terminal insomnia in patients homozygous for the Clock genotype. Other genes have been shown to contribute to sleep pathologies. A point mutation in the prion protein gene appears to be the cause of fatal familial insomnia. A missense mutation has been found in the gene encoding the GABA-A beta 3 subunit in a patient with chronic insomnia. In both animal models and humans, a deficiency in the hypocretin/orexin system was proposed to be responsible for narcolepsy. Selective destruction of hypocretin neurons is the most probable culprit in humans. These findings suggest that the genetic contribution to sleep disorders and wake determinants is more important than originally thought. Beyond sleep, light/dark cycles and sleep deprivation appear also to be associated with eating habits, and epidemics of obesity have to be evaluated in the context of shortened sleep duration.

Less is more: pathophysiology of dopaminergic-therapy-related augmentation in restless legs syndrome

Therapy-related augmentation of the symptoms of restless legs syndrome (RLS) is an important clinical problem reported in up to 60% of patients treated with levodopa and, to a lesser extent, with dopamine agonists. The efficacy of low-dose dopaminergic drugs for RLS has been established, but the mode of action is unknown. Here, we review the existing data and conclude that augmentation is a syndrome characterised by a severely increased dopamine concentration in the CNS; overstimulation of the dopamine D1 receptors compared with D2 receptors in the spinal cord may lead to D1-related pain and generate periodic limb movements; iron deficiency may be a main predisposing factor of augmentation, probably caused by a reduced function of the dopamine transporter; therapy with levodopa or dopamine agonists should remain at low doses and; iron supplementation and opiates are the therapy of choice to counter augmentation.

Considering the causes of RLS

The pathophysiology of restless legs syndrome (RLS) is complex and remains to be fully elucidated. The condition is predominantly a disorder of the central rather than the peripheral, nervous system, and dopaminergic dysfunction in subcortical systems appears to play a central role. Conditions associated with secondary RLS, such as pregnancy or end-stage renal disease, are characterized by iron deficiency, which suggests that disturbed iron homeostasis may also play a role in the development of the condition. Although most patients with RLS have normal serum ferritin levels, concentrations of ferritin and transferrin in the cerebrospinal fluid are reduced, suggesting iron deficiency within the central nervous system. Although iron is necessary for the activity of tyrosine hydroxylase, the rate-limiting step in dopamine synthesis, it is unclear whether this relationship plays a role in the aetiology of RLS. There also appears to be a genetic component, particularly when the condition develops before the age of 45 years. Candidate genetic loci have been located on chromosomes 9p, 12q and 14q, but the genes involved have yet to be identified. How these three identified aetiological factors, namely dopaminergic dysfunction, impaired iron homeostasis and genetic disposition, are inter-related in the genesis of RLS remains unclear.

Restless legs syndrome: a review

Restless legs syndrome (RLS) is a sensorimotor disorder characterized by an irresistible urge to move the limbs accompanied by uncomfortable sensations, leading to sleep disturbances. It is associated with psychiatric comorbidities and a decreased quality of life. RLS is common and most severe among females and the elderly. It may be primary or secondary to other conditions and may be familial. Linkage to several chromosomal loci have been demonstrated. The pathogenesis of RLS involves dopaminergic dysfunction, iron metabolism, and abnormalities in supraspinal inhibition. The mainstay of RLS therapy are dopamine agonists or levodopa. This article reviews the clinical characteristics, epidemiology, diagnosis, pathogenesis, and treatment of RLS.

Genetics of restless legs syndrome

Several studies on restless legs syndrome (RLS) have suggested a substantial genetic contribution in the etiology of this sleep disorder. Clinical surveys of idiopathic RLS patients have shown that 40-90% report a positive family history. The clinical features have been compared between familial and sporadic cases and the only difference found was a younger age-at-onset in familial RLS. Despite several reports suggesting a genetic contribution to the etiology of idiopathic RLS, few molecular genetic studies have been carried out attempting to identify genes that can predispose to this disorder. In particular, genes encoding for the GABA A receptor subunits, the gene for the alpha1 subunit of the glycine receptor, and genes involved in dopaminergic transmission and metabolism have been analyzed, however no significant findings have been reported. Genomewide linkage analysis studies using microsatellite markers have identified three loci for RLS: on chromosome 12q, on chromosome 14q and on chromosome 9p. It is important to investigate whether further RLS families show linkage to one of these loci to discuss the contribution of these loci and to provide a prerequisite of a mutational screening and identification of the RLS genes.

Genetics of restless legs syndrome

Restless legs syndrome (RLS) is a common disorder, although under-diagnosed, with a prevalence of up to 15% depending on the population sampled. Familial aggregation has been widely shown since Ekbom formerly described the condition in 1960; twin studies support a genetic contribution in the development of this disorder. Molecular genetic approaches have identified three genomic regions in RLS susceptibility, however no specific mutations have yet been identified. Herein, we review the current status of genetics in RLS, providing some methodological guidelines to help future research.

Restless Legs Syndrome

Restless legs syndrome (RLS) is clinically defined as an urge to move the legs with or without paresthesia, worsening of symptoms with rest and transient improvement with activity, and worsening of symptoms in the evening and night. This is often genetic but may also occur in the setting of iron deficiency, uremia, pregnancy, neuropathy, and possibly other conditions. The pathology is probably related to central nervous system iron dysregulation. Effective treatments include dopaminergics and narcotics. Recent advances in our understanding of RLS clinical presentation, epidemiology, etiology, and treatment will be discussed.

The restless legs syndrome

The restless legs syndrome (RLS) is one of the commonest neurological sensorimotor disorders at least in the Western countries and is often associated with periodic limb movements (PLM) during sleep leading to severe insomnia. However, it remains largely underdiagnosed and its underlying pathogenesis is presently unknown. Women are more affected than men and early-onset disease is associated with familial cases. A genetic origin has been suggested but the mode of inheritance is unknown. Secondary causes of RLS may share a common underlying pathophysiology implicating iron deficiency or misuse. The excellent response to dopaminegic drugs points to a central role of dopamine in the pathophysiology of RLS. Iron may also represent a primary factor in the development of RLS, as suggested by recent pathological and brain imaging studies. However, the way dopamine and iron, and probably other compounds, interact to generate the circadian pattern in the occurrence of RLS and PLM symptoms remains unknown. The same is also the case for the level of interaction of the two compounds within the central nervous system (CNS). Recent electrophysiological and animals studies suggest that complex spinal mechanisms are involved in the generation of RLS and PLM symptomatology. Dopamine modulation of spinal reflexes through dopamine D3 receptors was recently highlighted in animal models. The present review suggests that RLS is a complex disorder that may result from a complex dysfunction of interacting neuronal networks at one or several levels of the CNS and involving numerous neurotransmitter systems.

Restless legs syndrome

Restless legs syndrome is a very common and still under-diagnosed neurologic condition that can cause severe morbidity. The pathology centers around central nervous system iron homeostatic dysregulation with subsequent alterations in dopaminergic functioning. Genetic studies will hopefully soon identify specific abnormalities. Treatment of restless legs syndrome with dopaminergic medications is highly effective, although augmentation may occur eventually and require dosing flexibility.