Segregation Analysis of Restless Legs Syndrome: Possible Evidence for a Major Gene in a Family Study Using Blinded Diagnoses

Restless Legs Syndrome: Contemporary Diagnosis and Treatment

Restless legs syndrome (RLS) is characterized by an uncomfortable urge to move the legs while at rest, relief upon movement or getting up to walk, and worsened symptom severity at night. RLS may be primary (idiopathic) or secondary to pregnancy or a variety of systemic disorders, especially iron deficiency, and chronic renal insufficiency. Genetic predisposition with a family history is common. The pathogenesis of RLS remains unclear but is likely to involve central nervous system dopaminergic dysfunction, as well as other, undefined contributing mechanisms. Evaluation begins with a thorough history and examination, and iron measures, including ferritin and transferrin saturation, should be checked at presentation and with worsened symptoms, especially when augmentation develops. Augmentation is characterized by more intense symptom severity, earlier symptom occurrence, and often, symptom spread from the legs to the arms or other body regions. Some people with RLS have adequate symptom control with non-pharmacological measures such as massage or temperate baths. First-line management options include iron-replacement therapy in those with evidence for reduced body-iron stores or, alternatively, with prescribed gabapentin or pregabalin, and dopamine agonists such as pramipexole, ropinirole, and rotigotine. Second-line therapies include intravenous iron infusion in those who are intolerant of oral iron and/or those having augmentation with intense, severe RLS symptoms, and opioids including tramadol, oxycodone, and methadone. RLS significantly impacts patients' quality of life and remains a therapeutic area sorely in need of innovation and a further pipeline of new, biologically informed therapies.

Pleiotropic genetic effects influencing sleep and neurological disorders

Research evidence increasingly points to the large impact of sleep disturbances on public health. Many aspects of sleep are heritable and genes influencing traits such as timing, EEG characteristics, sleep duration, and response to sleep loss have been identified. Notably, large-scale genome-wide analyses have implicated numerous genes with small effects on sleep timing. Additionally, there has been considerable progress in the identification of genes influencing risk for some neurological sleep disorders. For restless legs syndrome, implicated variants are typically in genes associated with neuronal development. By contrast, genes conferring risk for narcolepsy function in the immune system. Many genetic variants associated with sleep disorders are also implicated in neurological disorders in which sleep abnormalities are common; for example, variation in genes involved in synaptic homoeostasis are implicated in autism spectrum disorder and sleep-wake control. Further investigation into pleiotropic roles of genes influencing both sleep and neurological disorders could lead to new treatment strategies for a variety of sleep disturbances.

Phenocopies in families with essential tremor and restless legs syndrome challenge Mendelian laws. Epigenetics might provide answers

Essential Tremor (ET) and Restless Legs Syndrome (RLS) are both highly heritable neurological disorders. The frequent occurrence of multi-incident families suggests the existence of highly penetrant alleles. However, linkage analyses and positional cloning approaches performed within the last 10 years essentially failed to identify responsible mutations. Several loci were found, but their relevance was questioned given the occurrence of suspected phenocopies in many of those families. Remarkably, in some ET and RLS families with an apparent autosomal dominant mode of transmission, the proportion of affected individuals was higher than the expected 50% and therefore suggests a non-mendelian inheritance in some cases. In fact, there is increasing evidence that epigenetic modifications, which refer to changes in gene expression without changes in DNA sequence, can be transmitted to the next generation. Moreover, epigenetic information can be transferred from one allele of a gene to the other allele of the same gene; if then inherited to the next generation, the offspring consequently presents phenotypic properties related to the untransmitted allele. This phenomenon known as paramutation is well documented in plants and has recently been shown to occur also in mammals. Here, I explore the possibility that it is the epigenetic and not only the genetic state which confers disease risk in families. Inheritance of epigenetic mutations along with paramutational events have the potential to explain the non-mendelian features in the genetics of both diseases.

Restless legs syndrome, periodic leg movements, and periodic limb movement disorder in children

The characteristic symptoms of restless legs syndrome (RLS) have been known for hundreds of years and were first reported in medicine in the 1600s. Clinicians must consider potential mimics, comorbid, and associated conditions when evaluating children with RLS symptoms. The traditional differentiation of RLS from periodic limb movement disorder (PLMD) is noted in children as well as adults. Because current pediatric RLS research is sparse, this article provides the most up-to-date evidence-based as well as consensus opinion-based information on the subject of childhood RLS and PLMD. Prevalence, pathophysiology, diagnosis, treatment, and clinical associations are discussed.

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.

Pregnancy accounts for most of the gender difference in prevalence of familial RLS

OBJECTIVE

This study was designed to evaluate the associated risk of RLS with pregnancy in relation to the family history and the age of symptom onset of RLS.

METHODS AND SUBJECTS

Data from a prior RLS family history study in which 1019 subjects (527 males, 492 females) were interviewed, provided a diagnosis and characterization of RLS and determination of pregnancy status on which the current study analysis was undertaken.

RESULTS

In the family members of RLS probands, the prevalence of RLS was significantly higher for parous women than for nulliparous women (49.5% vs. 33.7%, OR=1.92, 95% CI=1.16-3.19) or for men (49.5% vs. 30.0%, OR 2.29, 1.69-3.10), but no different for nulliparous women compared to men (33.7% vs. 30.0%, OR 1.19, 0.72-1.96). When only those whose RLS started at or after age 30 were considered, similar differences occurred. These differences were not observed among family members of control probands.

CONCLUSIONS

These data indicate pregnancy has a major impact on the risk of developing RLS for those with a family history of RLS. This pregnancy effect appears to account for most of the gender differences often reported in overall RLS prevalence data.

The four diagnostic criteria for Restless Legs Syndrome are unable to exclude confounding conditions ("mimics")

BACKGROUND

Epidemiological survey studies have suggested that a large fraction of the adult population, from five to more than 10%, have symptoms of Restless Legs Syndrome (RLS). Recently, however, it has become clear that the positive predictive value of many questionnaire screens for RLS may be fairly low and that many individuals who are identified by these screens have other conditions that can "mimic" the features of RLS by satisfying the four diagnostic criteria. We noted the presence of such confounders in a case-control family study and sought to develop methods to differentiate them from true RLS.

METHODS

Family members from the case-control study were interviewed blindly by an RLS expert using the validated Hopkins telephone diagnostic interview (HTDI). Besides questions on the four key diagnostic features of RLS, the HTDI contains open-ended questions on symptom quality and relief strategies and other questions to probe the character of provocative situations and modes of relief. Based on the entire HDTI, a diagnosis of definite, probable or possible RLS or Not-RLS was made.

RESULTS

Out of 1255 family members contacted, we diagnosed 1232: 402 (32.0%) had definite or probable RLS, 42 (3.3%) possible RLS, and 788 (62.8%) Not-RLS. Of the 788 family members who were determined not to have RLS, 126 could satisfy all four diagnostic criteria (16%). This finding indicates that the specificity of the four criteria was only 84%. Those with mimic conditions were found to have atypical presentations whose features could be used to assist in final diagnosis.

CONCLUSION

A variety of conditions, including cramps, positional discomfort, and local leg pathology can satisfy all four diagnostic criteria for RLS and thereby "mimic" RLS by satisfying the four diagnostic criteria. Definitive diagnosis of RLS, therefore, requires exclusion of these other conditions, which may be more common in the population than true RLS. Short of an extended clinical interview and workup, certain features of presentation help differentiate mimics from true RLS.

Altered iron metabolism in lymphocytes from subjects with restless legs syndrome

OBJECTIVE

Studies using cerebrospinal fluid, magnetic resonance imaging, and autopsy tissue have implicated a primary role for brain iron insufficiency in restless legs syndrome (RLS). If the abnormalities of brain iron regulation reflect a basic disturbance of iron metabolism, then this might be expressed at least partially in some peripheral systems. Thus the study aim was to determine whether patients with RLS and control subjects show differences in lymphocyte iron regulator proteins.

METHODS

Fasting morning blood samples were used to obtain common serum measures of iron status and to determine lymphocyte iron management proteins. Twenty-four women with early-onset RLS and 25 control women without RLS symptoms were studied.

RESULTS

RLS and control subjects were matched for age, hemoglobin, and serum iron profile. However, transferrin receptor (TfR) and DMT1 (divalent metal transporter 1 protein) levels in lymphocytes were significantly higher for RLS patients than for controls. No significant differences in ferritin subtypes or transferrin levels were found. No significant correlations were found between lymphocyte and serum indices of iron status.

INTERPRETATION

RLS lymphocytes showed an increase in ferroportin, implying increased cellular iron excretion, in the face of increased iron need (increased TfR and DMT1). In the absence of changes in H-ferritin, the findings indicate a balance between input and output with no net iron change but probable overall increase in iron turnover. The lack of any significant correlation between serum and lymphocyte iron indices indicates that iron management proteins from lymphocytes are at a minimum an alternative and independent marker of cellular iron metabolism.

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]

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.

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.