Mutational analysis of neurotensin in familial 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.

The influence of parathyroidectomy on restless legs syndrome in patients with renal hyperparathyroidism

BACKGROUND

Restless legs syndrome (RLS) is a common and poorly understood movement disorder that leads to unpleasant leg sensations. Although RLS can be idiopathic, secondary etiologies such as iron deficiency and renal failure are common. The aim of this prospective cohort study was to evaluate whether RLS is a common feature in patients undergoing parathyroidectomy for renal hyperparathyroidism (rHPT) and if RLS-related symptoms can be influenced by surgery.

METHODS

After providing written consent, patients who underwent a parathyroidectomy for rHPT between January and November 2011 answered a validated RLS-screening-questionnaire (RLSSQ). If this was suggestive for RLS a confirming questionnaire (IRLS) was also completed on the day before surgery, on the fifth postoperative day, and again during follow-up (minimum 12 months). Perioperative parathyroid hormone and calcium levels, as well as the scores of the questionnaires were analyzed.

RESULTS

Twenty-one patients (14 men, 7 women) with a mean age of 47.8 ± 3.2 years underwent total parathyroidectomy with bilateral cervical thymectomy and parathyroid autotransplantation for rHPT. The mean score of the RLSSQ of all 21 patients prior to operation was 6.1 ± 0.5. In 10 of 21 patients (47.6 %) the results of the RLSSQ were suggestive for RLS with a mean score of 8.0 ± 0.3. The consecutive scores of the IRLS in these latter patients significantly dropped from 26.6 ± 1.4 to 19.0 ± 2.2 between the preoperative and postoperative settings (p < 0.05). After a mean follow-up of 17.3 ± 3.7 months the mean scores of the RLSSQ and the IRLS were 6.1 ± 0.6 and 16.3 ± 1.8.

CONCLUSIONS

rHPT may play a major role in the severity of RLS-associated symptoms in patients with renal failure. Consequently, parathyroidectomy may prove to be a valuable tool to reduce RLS-associated morbidity in affected patients. However, larger prospective trials are required to confirm the possible relation between RLS and rHPT seen in the present study

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.

Potential influences of complementary therapy on motor and non-motor complications in Parkinson's disease

Nearly two-thirds of patients with Parkinson's disease (PD) use vitamins or nutritional supplements, and many more may use other complementary therapies, yet <50% of patients have discussed the use of these complementary therapies with a healthcare professional. Physicians should be aware of the complementary therapies their patients with PD are using, and the possible effects of these therapies on motor and non-motor symptoms. Complementary therapies, such as altered diet, dietary supplements, vitamin therapy, herbal supplements, caffeine, nicotine, exercise, physical therapy, massage therapy, melatonin, bright-light therapy and acupuncture, may all influence the symptoms of PD and/or the effectiveness of dopaminergic therapy. Preliminary evidence suggests complementary therapy also may influence non-motor symptoms of PD, such as respiratory disorders, gastrointestinal disorders, mood disorders, sleep and orthostatic hypotension. Whenever possible, clinicians should ensure that complementary therapy is used appropriately in PD patients without reducing the benefits of dopaminergic therapy.

[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.

Genetic association studies of neurotensin gene and restless legs syndrome in French Canadians

BACKGROUND AND PURPOSE

The neurotensin gene (NTS), a known dopamine modulator, is located within the candidate region for the first genetic locus of restless legs syndrome (RLS1) on chromosome 12q. Though no causative mutation was found in selected patients in a previous mutation analysis, the involvement of NTS in RLS cannot be completely excluded as a potential positional and functional candidate gene. The purpose of the current study is to further explore the NTS gene for potential functional variant(s) in its entire genomic and potential regulatory regions and their possible association with RLS symptoms.

METHODS AND SUBJECTS

We resequenced the coding regions and sequenced all the intronic and potential regulatory regions of the NTS gene in additional patients and controls. We carried out full scale gene-based case-control and family-based genetic association studies using the sequence variants detected during mutational analysis.

RESULTS

No coding or variants in regulatory and intronic regions compatible with a deleterious mutation were detected. Seven polymorphisms with elevated allele frequencies in the Caucasian population did not show association with RLS in two independent case-control groups and 110 RLS families.

CONCLUSION

The NTS gene on chromosome 12q is most unlikely to play a direct role in RLS etiology.

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.

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.

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

PURPOSE

The signs and symptoms, epidemiology, etiology, pathophysiology, diagnosis, pharmacologic and nonpharmacologic treatments, and options and guidelines for the treatment of restless legs syndrome (RLS) are reviewed.

SUMMARY

RLS was first described in the 17th century and further characterized in 1945. RLS is a common disorder, occurring in about 10% of the population. Patients with RLS often describe the urge to move, uncomfortable sensations, and pain, which begin or worsen during rest or inactivity such as lying or sitting. Symptoms of RLS make sleeping difficult for many patients, and significant daytime difficulties result from the condition. RLS can either be primary or arise from secondary causes that lead to iron deficiency. There is a familial component in primary RLS, but its underlying mechanisms remain unknown. Of individuals with conditions associated with iron-deficiency states, including pregnancy, renal failure, and anemia, 25-30% may develop RLS. The goals of RLS treatment include improving its symptoms and the patient's quality of life. There are limited data on the treatment of RLS. Pharmacologic therapies include iron replacement, dopaminergic agents (e.g., levodopa), dopamine agonists, anticonvulsants, opioids, and benzodiazepines. There have been no systematic trials of nonpharmacologic therapies for RLS, but good sleep hygiene and avoidance of alcohol, caffeine, and nicotine may improve symptoms.

CONCLUSION

RLS is a common disorder thought to involve abnormal iron metabolism and dopaminergic systems. Nonpharmacologic therapy should be suggested for all patients with RLS, but pharmacologic therapy may be required, and evidence is strongest for levodopa and dopamine agonists.

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.

The restless legs syndrome

The restless legs syndrome is a common disorder that encompasses an idiopathic form of genetic or unknown origin and symptomatic forms associated with many causes. Symptomatic forms occur during pregnancy and are coincident with uraemia, iron depletion, polyneuropathy, spinal disorders, and rheumatoid arthritis. For the hereditary forms, at least three gene loci, located on chromosomes 12, 14, and 9, have been traced so far. Prevalence in the general population is between 3% and 9%, increases with age, and is higher in women than in men. Treatment is needed only in the moderate to severe forms of the disorder and mostly in elderly people. Pathophysiology and treatment may be closely linked to the dopaminergic system and iron metabolism. Dopaminergic treatment with levodopa and dopamine agonists is the first choice in idiopathic restless legs syndrome, but augmentation and rebound should be monitored in long-term treatment. Various other drugs, such as opioids, gabapentin, and benzodiazepines, provide alternative treatment possibilities.

Genetics of normal and pathological sleep in humans

The complexity of sleep-wake regulation, in addition to the many environmental influences, includes genetic predisposing factors, which begin to be discovered. Most of the current progress in the study of sleep genetics comes from animal models (dogs, mice, and drosophila). Multiple approaches using both animal models and different genetic techniques are needed to follow the segregation and ultimately to identify 'sleep genes' and molecular bases of sleep disorders. Recent progress in molecular genetics and the development of detailed human genome map have already led to the identification of genetic factors in several complex disorders. Only a few genes are known for which a mutation causes a sleep disorder. However, single gene disorders are rare and most common disorders are complex in terms of their genetic susceptibility, environmental factors, gene-gene, and gene-environment interactions. We review here the current progress in the genetics of normal and pathological sleep and suggest a few future perspectives.

Genes for normal sleep and sleep disorders

Sleep and wakefulness are complex behaviors that are influenced by many genetic and environmental factors, which are beginning to be discovered. The contribution of genetic components to sleep disorders is also increasingly recognized as important. Point mutations in the prion protein, period 2, and the prepro-hypocretin/orexin gene have been found as the cause of a few sleep disorders but the possibility that other gene defects may contribute to the pathophysiology of major sleep disorders is worth in-depth investigations. However, single gene disorders are rare and most common disorders are complex in terms of their genetic susceptibility, environmental effects, gene-gene, and gene-environment interactions. We review here the current progress in the genetics of normal and pathological sleep.