Decreased transferrin receptor expression by neuromelanin cells in restless legs syndrome

Substantia nigra hypoechogenicity: definition and findings in restless legs syndrome

Pathological studies demonstrate a decreased iron content in the substantia nigra (SN) contributing to the pathophysiology of restless legs syndrome (RLS). SN echogenicity as measured by transcranial sonography (TCS) correlates with the SN iron content. The objective of this study was to determine a critical value to define SN hypoechogenicity as a potential marker for RLS. There were 49 RLS patients (39 idiopathic, 10 secondary) and 49 age- and sex-matched controls who underwent TCS by 2 independent and blinded examiners to determine the area of SN echogenicity. We found that SN echogenicity is significantly decreased in RLS patients compared to healthy controls (P < 0.001). SN hypoechogenicity (sum area of SN echogenicity of both sides < 0.2 cm(2)) is more common in idiopathic than in secondary RLS patients. The area under curve for idiopathic RLS versus controls (receiver operating characteristics) is 0.91, specificity is 0.90, and sensitivity is 0.82. TCS provides an interesting additional instrument in the diagnosis of RLS. Therefore, SN hypoechogenicity (SN sum area < 0.2 cm(2)), which is supposed to indicate a decreased SN iron content, is a marker for RLS. Further studies are needed to investigate its significance for the pathophysiology of this frequent movement disorder and possible clinical applications.

Differential expression of genes in amyotrophic lateral sclerosis revealed by profiling the post mortem cortex

The possible causes of ALS are unknown and multiple biological systems have been implicated. The goal of this study was to use gene expression profiling to evaluate a broad spectrum of systems in ALS. For this study, the medial lip of the human motor cortex and adjacent sensory cortex were collected at autopsy from five ALS patients and three normal individuals. Quantitative filter analysis revealed differential expression of mRNAs normalized to internal standards. A significant difference in expression of 275 genes was found in the ALS motor cortex; of the genes whose expression was changed, 10 were up-regulated and 265 were down-regulated. Six of the up-regulated genes were associated with cell surface activity and two were glutamate receptors; the latter is potentially consistent with the idea of excitotoxicity contributing to neurodegeneration in ALS. Of the down-regulated genes, the largest number were associated with transcription followed by those involved in antioxidant systems, inflammation, regulation of motor neuron function, lipid metabolism, protease inhibition, and protection against apoptosis including vascular endothelial growth factor. There were no significant differences in gene expression patterns between the sensory and motor cortex in the ALS brains. A total of 10% of the genes identified by microarray were chosen from each of the gene groups for validation by quantitative real time PCR (QRT-PCR). In order to increase the reliability of our gene array data, newly acquired motor and sensory cortex of ALS and control cases (n = 4 each) were used for validation. Of these, 86.4% changed in the same direction as determined in the microarrays. The gene profile data reported here are consistent with evidence that the ALS brain is characterized by an environment that is permissive for apoptosis, excitotoxicity and abnormal ubiquitination. This gene array study also suggested that a metal imbalance particularly for zinc could exist in ALS. Finally, given the amount of cellular stress that is thought to be part of the pathogenesis in ALS, there was a notable lack of increase in genes required to mount a protective response. This latter observation provides a conceptual framework in which to consider the possibility that ALS could result from a failure to mount adequate protective responses to physiological insults that, left unchecked, could progress to neurodegeneration.

Controversies and challenges in defining the etiology and pathophysiology of restless legs syndrome

Restless legs syndrome (RLS) can occur as a primary disorder, with no apparent cause other than a possible genetic predisposition, or as a secondary condition, most commonly related to iron deficiency, pregnancy, or end-stage renal disease. Recent studies have identified 2 different phenotypes of RLS based on age at onset of symptoms. Persons whose RLS symptoms start at an earlier age (<45 years) are more likely to have a family history of RLS and tend to have a more slowly progressive development of the disorder compared with individuals who have later onset of symptoms. In the past, our ability to determine either prevalence or population factors associated with increased occurrence of RLS has been limited. However, 4 different diagnostic criteria have been established. Familiarity with diagnostic criteria and clinical characteristics are essential for diagnosis and appropriate treatment, if required.

The role of iron in restless legs syndrome

The impressive relief from restless legs syndrome (RLS) symptoms provided by levodopa treatment indicates RLS is caused by a dopaminergic abnormality. But similar and more lasting relief also occurs for iron treatment in some patients. Thus there are two major putative causes for RLS: CNS dopaminergic abnormality and CNS iron insufficiency. This article presents the data documenting that both peripheral and CNS iron insufficiency occur with RLS symptoms. Brain iron insufficiency is supported by independently replicated cerebrospinal fluid and brain imaging studies for patients without iron deficiency (ID) anemia. Autopsy studies and intravenous iron treatment further link brain iron insufficiency to RLS. The brain iron insufficiency in patients with RLS is now well established. In this article the data are reviewed that support the following postulates combining dopaminergic and iron causes of RLS: (1) All conditions that compromise iron availability will increase the risk of RLS leading to a higher than expected prevalence of RLS in these conditions. (2) Some patients with RLS have marginal CNS iron status that can become insufficient when deprived of normal access to adequate peripheral iron or may be insufficient even with normal access to adequate peripheral iron. (3) The change or reduced CNS iron status produces RLS symptoms largely through its effects on the dopaminergic system and the corollary to 3. (4) Dopaminergic system abnormalities producing RLS symptoms will be included in those produced by brain ID. Study of the iron model of RLS offers hope for developing new treatment approaches and perhaps methods to prevent or cure the disorder.

Restless Legs Syndrome

Restless legs syndrome (RLS) is a common and often disabling sensorimotor disorder. Epidemiologic studies suggest that RLS is an underrecognized and undertreated disorder affecting both children and adults. The diagnosis is based primarily on the following four essential criteria: (1) an urge to move, usually associated with paresthesias, (2) onset or exacerbation of symptoms at rest, (3) relief of symptoms with movement, and (4) symptoms manifesting in a circadian pattern. Supplemental workup including polysomnography, iron profile, and/or neuropathy screen can provide support for the diagnosis and aid in the treatment strategy. Behavioral techniques, dopaminergic agents, opiates, benzodiazepines, and antiepileptics all have potential value in treating this disorder. Dopaminergic agents continue to be the most effective RLS treatment. However, due to their potential long-term side effects, these agents should not be considered the sole treatment of choice. In the end, the therapeutic plan should be individualized to suit each patient's presentation and needs.

Is ferroportin–hepcidin signaling altered in restless legs syndrome?

Restless legs syndrome (RLS) is a neurological disorder characterized by a strong urge to move the legs. Sufferers of RLS often experience chronic sleep deprivation, due to the characteristic worsening of symptoms both when at rest and during the night. MRI data, autopsy studies, and a consistent decrease in CSF ferritin all suggest that early-onset RLS is associated with insufficient iron in the brain. In this study, we examined the relationship between the iron regulatory hormone hepcidin and RLS. Hepcidin serves as a hormone that signals iron release from cells by interacting with ferroportin. We measured the expression and concentration of pro-hepcidin in the brain and cerebrospinal fluid of both RLS patients and control individuals. In CSF, we found that pro-hepcidin levels were significantly decreased in early-onset RLS patient samples, but not in late-onset RLS patients, when compared to controls. Conversely, in neuromelanin cells, substantia nigra, and putamen, the concentration of pro-hepcidin in RLS samples is significantly increased compared to controls. Functionally, hepcidin binds to ferroportin to limit iron movement from cells. Therefore, we provide immunocytochemical evidence that ferroportin is expressed by the epithelial cells of the choroid plexus and the ependymal cells lining the ventricles. These data suggest that sites of action for hepcidin include signaling the ventricular system for movement between brain and CSF. At this time, it cannot be determined if the lower levels of pro-hepcidin in the CSF represent a compensatory response to the decreased levels of iron in the brain or a defective signaling mechanism in RLS. Nonetheless, these data support the mounting evidence that there is a biological basis for RLS and the underlying mechanism involves iron management.

MRI-determined regional brain iron concentrations in early- and late-onset restless legs syndrome

OBJECTIVE

Cerebrospinal fluid (CSF), magnetic resonance imaging (MRI) and autopsy studies have suggested that brain iron may be reduced in restless legs syndrome (RLS). Further analysis of the data also suggests that diminished brain iron may selectively be for early-onset RLS. This study was designed to replicate and extend our previous findings, specifically with regard to early-onset RLS. In this study our primary hypothesis was that substantia nigra (SN) iron index would be decreased in early-onset RLS compared to controls.

METHODS

The iron concentration or 'iron index' in 10 brain regions was determined using MRI in 39 controls and in 22 early-onset and 19 late-onset RLS subjects. The Johns Hopkins RLS severity (JHRLSS) scale was used to define disease severity.

RESULTS

The mean iron index from the SN was significantly lower in the early-onset RLS compared to controls (t=2.5, P=0.016), while late-onset RLS and controls did not differ. There was a significant negative Spearman rank correlation between SN iron index and JHRLSS scale for the control-early-onset-RLS cohort (rho=-0.32, P=0.016).

CONCLUSIONS

The current MRI results in combination with previous autopsy data support the role of low brain iron in the SN in at least those with early-onset RLS symptoms.

Ferritin subunits in CSF are decreased in restless legs syndrome

Restless legs syndrome (RLS) is a neurological disorder that may be related to iron misregulation at the level of the central nervous system. Evidence that iron is involved in RLS comes from magnetic resonance imaging data, autopsy studies, analyses of cerebrospinal fluid (CSF), and correlations of symptoms with serum ferritin. To further examine the possibility that brain iron status is insufficient in RLS, we determined ferritin levels in the CSF. Specifically, we differentiated between the H- and L-subunits of ferritin, because these peptides are expressed from different chromosomes and have different functions. We measured H- and L-ferritin subunit levels in control and RLS human CSF using immunoblot analysis and found that both H- and L-ferritin are significantly decreased in early but not late-onset RLS. Additionally, we quantified total protein in each CSF sample to establish that the decrease in ferritin subunits in RLS did not reflect a decrease in total protein in CSF. Furthermore, we used equal amounts of total CSF protein in the immunoblot analyses, in contrast to previously published studies that provided only volumetric data, to determine which approach was more accurate for quantifying the amount of ferritin relative to other proteins in CSF. Our results establish a protein standard in RLS, provide a comparative analysis of protein-controlled versus volumetric immunoblot techniques, and argue for a profound loss of iron storage capacity in the brain in RLS, specifically in the early onset RLS phenotype. These data suggest that CSF ferritin levels may provide a biomarker for assisting in the diagnosis of RLS.

Ropinirole: use in restless legs syndrome

Ropinirole is a nonergoline dopamine agonist indicated for the treatment of Parkinson’s disease as monotherapy or combination therapy. However, recent studies have demonstrated a role for this drug in the treatment of restless legs syndrome. Dopaminergic agents, such as ropinirole, are considered the first-line treatment for restless legs syndrome. The dosage of ropinirole needed to treat the symptoms of restless legs syndrome appears to be much smaller (0.25–4.0 mg/day) than that necessary for Parkinson’s disease therapy. Ropinirole is generally well tolerated, with no serious adverse effects. The adverse effects of ropinirole are comparable with those of other dopamine agonists, including nausea and dizziness. In contrast to ergoline substances, ropinirole is free from retroperitoneal, pleural, pericardial fibroses and restrictive valvular heart disease. Clinical studies have indicated that ropinirole reduces the motor symptoms of restless legs syndrome effectively and improves sleep quantity and quality.

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

OBJECTIVE

The objective of this study was to ascertain the most likely inheritance pattern of restless legs syndrome (RLS) using segregation analysis.

METHODS

Probands were RLS patients presenting to the Neurology and Sleep clinics of the Johns-Hopkins Bayview medical center with willing first and second degree relatives. Blinded diagnosis was made in those who exhibited the four diagnostic features of RLS. Analysis was performed on RLS as a dichotomous trait and considering age of onset models on 590 phenotyped subjects from 77 pedigrees.

RESULTS

All non-genetic models were rejected considering RLS as a dichotomous trait. A single locus Mendelian dominant model with gender as a covariate had best fit with allele frequency of 0.077 and complete penetrance. RLS frequency in non-carrier subjects was estimated to be 0.14. Two underlying distributions of age of onset, with a possible dichotomy at 26.3 years, were identified. Contrary to the results for RLS as a dichotomous trait, age of onset models did not indicate single major gene inheritance.

CONCLUSION

This segregation analysis suggests that the pattern of segregation is consistent with that of a single major locus, when RLS is treated as a dichotomous trait without considering age of onset. The high rate of phenocopies matches known population frequencies and taken with significant residual familial effects and the lack of evidence for a major gene controlling age of onset, indicates that non-genetic causes of RLS may exist and RLS is a complex disorder.

Ropinirole in the treatment of patients with restless legs syndrome: a US-based randomized, double-blind, placebo-controlled clinical trial

OBJECTIVE

To assess the efficacy, safety, and tolerability of the dopamine agonist ropinirole in the treatment of patients with moderate to severe primary restless legs syndrome (RLS).

PATIENTS AND METHODS

This multicenter, 12-week, double-blind, placebo-controlled, flexible-dose study enrolled US patients and was conducted between September 2003 and May 2004. Patients were randomized to ropinirole or placebo, 0.25-4.0 mg as needed and tolerated, once daily, 1 to 3 hours before bedtime. The primary end point was mean change from baseline to week 12 in International Restless Legs Scale (IRLS) total score. Key secondary efficacy measures included the Clinical Global Impression-Improvement scale.

RESULTS

A total of 381 patients were enrolled; 164 (87.7%) of 187 patients randomized to ropinirole and 167 (86.1%) of 194 randomized to placebo completed the study. Significant treatment differences favoring ropinirole, compared with placebo, were observed for change in IRLS total score at week 12 (adjusted mean treatment difference, -3.7; 95% confidence interval, -5.4 to -2.0; P < .001) and for all 3 key secondary end points: mean change from baseline in IRLS total score at week 1 and proportion of patients who were much/very much improved on the Clinical Global Impression Improvement scale at weeks 1 and 12. Ropinirole was associated with significantly greater Improvements in subjective measures of sleep disturbance, quantity, and adequacy; quality of life; and anxiety. Although treatment differences favoring ropinirole in daytime somnolence were observed, they were not statistically significant (P = .10). Ropinirole was generally well tolerated, with an adverse-event profile consistent with other dopamine agonists.

CONCLUSION

This study confirms that ropinirole improves RLS symptoms and subjective measures of sleep, quality of life, and anxiety and that it is generally well tolerated.

Transcranial ultrasound shows nigral hypoechogenicity in restless legs syndrome

In patients with Parkinson's disease, hyperechogenicity of the substantia nigra using transcranial ultrasound has been related to increased tissue concentrations of iron. Recently, deficient iron transport mechanisms in substantia nigra neurons have been described in postmortem tissue of patients with restless legs syndrome (RLS). This study was performed to study substantia nigra echogenicity in RLS patients compared with normal control subjects and Parkinson's disease patients. RLS patients had significantly reduced midbrain areas of hyperechogenicity compared with control subjects, and even more markedly reduced hyperechogenicity compared with Parkinson's disease patients. These findings lend further support to nigral iron deficiency as a pathogenetic factor in RLS.

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.

Laser microdissection in CNS research

The complexity of the brain makes the investigation of anatomically defined regions using manual dissection techniques problematic. With these manual dissection techniques, only a mixture of many different cell types can be obtained. This leads to averaging the contents of all the different cell types, making it nearly impossible to observe effects that are specific to one type of cell. Laser microdissection enables individual cell-types to be dissected accurately from the brain for subsequent analysis of the genome, proteome or, most frequently, the transcriptome. Investigating only functionally relevant cells with high specificity provides unambiguous data, resulting in faster identification of potential targets, the elucidation of drug mode-of-action, as well as aiding identification of biomarkers for diagnostics use.

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

PURPOSE OF REVIEW

In the review period since February 2004 a number of papers have been published that make significant contributions to the current understanding of the epidemiology, clinical assessment, pathophysiology and treatment of restless legs syndrome. Those with the most significant findings were selected and will be reviewed.

RECENT FINDINGS

Several epidemiological studies about restless legs syndrome have become available in the review period. A new susceptibility locus for restless legs syndrome has been reported. Neuropathological studies have provided profound insights into the key role of iron regulation in the pathophysiology of restless legs syndrome. Several randomized, double-blind, placebo-controlled studies have demonstrated that dopamine agonists are efficacious in the treatment of restless legs syndrome. A few pilot treatment studies with intravenous iron have been performed.

SUMMARY

In this paper, recent advances in the field of restless legs syndrome are reviewed. Special emphasis is placed on pathophysiology and treatment. Restless legs syndrome is still an underdiagnosed disorder. The evidence basis for its treatment has been considerably increased in the review period.

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.

Restless Legs Syndrome

RLS is a common condition that is likely to be encountered by primary care physicians in their practice. The currently available medications are highly effective in treating RLS. The knowledge of clinical presentation and diagnostic features of RLS will empower the primary care practitioners to effectively treat their patients who have RLS.

Iron, brain ageing and neurodegenerative disorders

There is increasing evidence that iron is involved in the mechanisms that underlie many neurodegenerative diseases. Conditions such as neuroferritinopathy and Friedreich ataxia are associated with mutations in genes that encode proteins that are involved in iron metabolism, and as the brain ages, iron accumulates in regions that are affected by Alzheimer's disease and Parkinson's disease. High concentrations of reactive iron can increase oxidative-stress induced neuronal vulnerability, and iron accumulation might increase the toxicity of environmental or endogenous toxins. By studying the accumulation and cellular distribution of iron during ageing, we should be able to increase our understanding of these neurodegenerative disorders and develop new therapeutic strategies.

Thy1 expression in the brain is affected by iron and is decreased in Restless Legs Syndrome

Thy-1 is a cell adhesion molecule that plays a regulatory role in the vesicular release of neurotransmitters. The objective of this study is to examine the relationship between iron status and Thy1 expression in neuronal systems of varying complexity. Pheochromocytoma cell (PC12) cells were used to explore whether there was a direct relation between cellular iron status and Thy1 expression. Iron chelation significantly decreased expression of Thy1 in PC12 cells in a dose and time dependent manner. Transferrin receptor expression was increased with iron chelation demonstrating that a global decrease in protein synthesis could not account for the Thy1 changes. We also examined brain homogenates from adult rats that were nursed by dams on an iron deficient (ID) diet and found a significant decrease in Thy1 compared to control rats. Finally, the substantia nigra from individuals with Restless Legs Syndrome reportedly has lower than normal amounts of iron. Therefore, we examined this brain region from individuals with the clinical diagnosis of primary Restless Legs syndrome (RLS) and found the concentration of Thy1 was less than half that of controls. The results of these studies support the novel concept that there is a relationship between Thy1 and iron and point to a novel mechanism by which iron deficiency can affect brain function. They also indicate a possible mechanism by which iron deficiency compromises dopaminergic transmission in RLS, providing a potentially important link between decreased brain iron and the responsiveness to levodopa and iron supplementation treatment in RLS.