Fine mapping and genetic heterogeneity in the pure form of autosomal dominant familial spastic paraplegia

We evaluated seven families segregating pure, autosomal dominant familial spastic paraplegia (SPG) for linkage to four recently identified SPG loci on chromosomes 2q (1), 8q (2), 12q (3), and 19q (4). These families were previously shown to be unlinked to SPG loci on chromosomes 2p, 14q, and 15q. Two families demonstrated linkage to the new loci. One family (family 3) showed significant evidence for linkage to chromosome 12q, peaking at D12S1691 (maximum lod=3.22). Haplotype analysis of family 3 did not identify any recombinants among affected individuals in the 12q candidate region. Family 5 yielded a peak lod score of 2.02 at marker D19S868 and excluded linkage to other known SPG loci. Haplotype analysis of family 5 revealed several crossovers in affected individuals, thereby potentially narrowing the SPG12 candidate region to a 5-cM region between markers D19S868 and D19S220. Three of the families definitively excluded all four loci examined, providing evidence for further genetic heterogeneity of pure, autosomal dominant SPG. In conclusion, these data confirm the presence of SPG10 (chromosome 12), potentially reduce the minimum candidate region for SPG12 (chromosome 19q), and suggest there is at least one additional autosomal dominant SPG locus. Electronic Publication     

A novel NF-L mutation Pro22Ser is associated with CMT2 in a large Slovenian family

Charcot-Marie-Tooth (CMT) disease is the most-common form of inherited motor and sensory neuropathy. The autosomal dominant axonal form of the disease (CMT2) is currently subdivided into seven types based on genetic localization. These are CMT2A (1p35-p36), CMT2B (3q13-q22), CMT2C (unknown), CMT2D (7p14), CMT2E (8p21), HMNSP (3q13.1), and CMT2F (7q11-q21). Two loci have thus far been identified for autosomal recessive CMT2; ARCMT2A (1q21.1-q21.3) and ARCMT2B (19q13.3). Mutations in four genes (connexin 32, myelin protein zero, neurofilament-light, and kinesin) have been associated with the CMT2 phenotype. We identified a novel neurofilament-light missense mutation (C64T) that causes the disease in a large Slovenian CMT2 family. This novel mutation shows complete co-segregation with the dominantly inherited CMT2 phenotype in our family. Electronic Publication     

A new dominant spinocerebellar ataxia linked to chromosome 19q13.4-qter

BACKGROUND: The autosomal dominant spinocerebellar ataxias (SCAs) are a clinically and genetically heterogeneous group of neurodegenerative disorders. Although molecular genetic studies have so far implicated 16 loci in the etiology of these diseases, approximately 30% of families with SCAs remain unlinked. OBJECTIVES: To report the location of a gene causing a "pure" autosomal dominant cerebellar ataxia in one family and to describe the clinical phenotype. PATIENTS: We have identified a 4-generation American family of English and Dutch ethnicity with a pure cerebellar ataxia displaying an autosomal dominant pattern of inheritance. The disease typically has its onset in the third and fourth decades of life, shows no evidence of anticipation, progresses slowly, and does not appear to decrease life expectancy. Clinical DNA testing excluded SCA1, 2, 3, 6, 7, and 8. METHODS: A genome-wide linkage analysis at a 10 centimorgan (cM) level was performed with samples from 26 family members (11 affected, 10 clinically unaffected at risk, and 5 spouses). RESULTS: Assuming 90% penetrance, we found suggestive evidence of linkage to chromosome 19, with a lod score of 2.49 for D19S571. More detailed mapping in this region provided a maximum 2-point lod score of 2.57 at theta = 0 for D19S254 and a maximum multipoint lod score of 4.72 at D19S926. By haplotype construction a 22-cM critical region from D19S601 to the q telomere was defined. CONCLUSIONS: We have mapped a gene for an autosomal dominant SCA to chromosome 19q13.4-qter in one family. The critical region overlaps with the locus for SCA14, a disease described in a single Japanese family and characterized by axial myoclonus. Myoclonus was not seen in the family we studied, but it remains possible that the 2 disorders are allelic variants.     

Locus heterogeneity, anticipation and reduction of the chromosome 2p minimal candidate region in autosomal dominant familial spastic paraplegia

We examined 11 Caucasian pedigrees with autosomal dominant ‘uncomplicated’ familial spastic paraplegia (SPG) for linkage to the previously identified loci on chromosomes 2p, 14q and 15q. Chromosome 15q was excluded for all families. Five families showed evidence for linkage to chromosome 2p, one to chromosome 14q, and five families remained indeterminate. Homogenity analysis of combined chromosome 2p and 14q date gave no evidence for a fourth as yet unidentified SPG locus. Recombination events reduced the chromosome 2p minimum candidate region (MCR) to a 3 cM interval between D2S352 and D2S367 and supported the previously reported 7 cM MCR for chromosome 14q. Age of onset (AO) was highly variable, indicating that subtypes of SPG are more appropriately defined on a genetic basis than by AO. Comparison of AO in parent-child pairs was suggestive of anticipation, with a median difference of 9.0 years (p <0.0001). Received March 13, 1997; Revised and Accepted April 29, 1997     

Analysis of the DNA duplication 17p11.2 in Charcot-Marie-Tooth neuropathy type 1 pedigrees: additional evidence for a third autosomal CMT1 locus.

We have restudied two clinically typical Charcot-Marie-Tooth neuropathy type 1 (CMT1; also known as hereditary motor and sensory neuropathy 1) pedigrees that were previously reported to be unlinked to the regions of proximal chromosome 1q and chromosome 17p by multipoint linkage analyses. In these two pedigrees, there is no evidence for linkage to additional DNA markers that flank and span the CMT1A locus on chromosome 17p11.2, and a duplication associated with CMT1A is not present in these pedigrees. These findings confirm that the CMT1 locus in these two pedigrees does not map to chromosome 17p11.2 or 1q, and provide further evidence for the existence of a third autosomal locus for CMT1.     

Confirmation of a second locus for CMT2 and evidence for additional genetic heterogeneity

The Charcot-Marie-Tooth (CMT) neuropathies are a group of disorders exhibiting neurophysical, pathological and genetic heterogeneity. CMT2 is a diagnostic subtype of this group of disorders characterized by variable expression and age-of-onset and normal or slightly diminished nerve conduction velocities. Previously, linkage and heterogeneity had been reported in CMT2 with linked families localizing to chromosome 1p (CMT2A). Recently a second CMT2 locus has been described on chromosome 7 in a single large CMT2 family (CMT2D). We have performed pedigree linkage analysis on 15 CMT2 families (N = 371 individuals, 106 affected family members) and have confirmed linkage to chromosome 7. Furthermore, using both admixture and multipoint linkage analysis we show conclusive evidence for additional heterogeneity within this clinical subtype with evidence of families that exclude linkage to both the CMT2D and CMT2A regions. In addition, unlike the previous report we found no abvious consistend clinical differences between the linked family types. Received February 28, 1997; Revised and Accepted April 7, 1997     

Benign familial infantile convulsions: linkage to chromosome 16p12-q12 in 14 families

PURPOSE: Benign familial infantile convulsions (BFIC) is a form of idiopathic epilepsy. It is characterized by clusters of afebrile seizures occurring around the sixth month of life. The disease has a benign course with a normal development and rare seizures in adulthood. Previous linkage analyses defined three susceptibility loci on chromosomes 19q12-q13.11, 16p12-q12, and 2q23-31. However, a responsible gene has not been identified. We studied linkage in 16 further BFIC families. METHODS: We collected 16 BFIC families, without an additional paroxysmal movement disorder, of German, Turkish, or Japanese origin with two to eight affected individuals. Standard two-point linkage analysis was performed. RESULTS: The clinical picture included a large variety of seizure semiologies ranging from paleness and cyanosis with altered consciousness to generalized tonic-clonic seizures. Interictal EEGs showed focal epileptiform discharges in six patients, and three ictal EEGs in three distinct patients revealed a focal seizure onset in different brain regions. In all analyzed families, we found no evidence for linkage to the BFIC loci on chromosomes 19q and 2q, as well as to the known loci for benign familial neonatal convulsions on chromosomes 8q and 20q. In 14 of the families, the chromosome 16 locus could be confirmed with a cumulative maximum two-point lod score of 6.1 at marker D16S411, and the known region for BFIC could be narrowed to 22.5 Mbp between markers D16S690 and D16S3136. CONCLUSIONS: Our data confirm the importance of the chromosome 16 locus for BFIC and may narrow the relevant interval.     

A novel locus for dominant cerebellar ataxia (SCA14) maps to a 10.2-cM interval flanked by D19S206 and D19S605 on chromosome 19q13.4-qter

Dominantly inherited, late-onset pure cerebellar ataxia is a group of genetically heterogeneous neurodegenerative disorders. Approximately half of these disorders in the Japanese population are caused by moderate expansion of a CAG repeat in the coding region of the CACNA1A gene on chromosome 19p13 (SCA6). However, neither the loci nor the specific mutations for the remaining disorders have been determined. We performed systematic linkage analysis in a three-generation Japanese family with a locus or mutation that differed from those of known spinocerebellar ataxias. The family members with a late onset (> or =39 years old) exhibited pure cerebellar ataxia, whereas those with an early onset (< or =27 years old) first showed intermittent axial myoclonus followed by ataxia. Other neurological signs were sparse, and neuroimaging studies revealed that atrophy was confined to the cerebellum. Multipoint analysis and haplotype reconstruction ultimately traced this novel spinocerebellar ataxia locus (SCA14) to a 10.2-cM interval flanked by D19S206 and D19S605 on chromosome 19q13.4-qter (Zmax = 4.08, corrected for age-dependent penetrance).     

Genome-wide scan of bipolar disorder in 65 pedigrees: supportive evidence for linkage at 8q24, 18q22, 4q32, 2p12, and 13q12

The purpose of this study was to assess 65 pedigrees ascertained through a Bipolar I (BPI) proband for evidence of linkage, using nonparametric methods in a genome-wide scan and for possible parent of origin effect using several analytical methods. We identified 15 loci with nominally significant evidence for increased allele sharing among affected relative pairs. Eight of these regions, at 8q24, 18q22, 4q32, 13q12, 4q35, 10q26, 2p12, and 12q24, directly overlap with previously reported evidence of linkage to bipolar disorder. Five regions at 20p13, 2p22, 14q23, 9p13, and 1q41 are within several Mb of previously reported regions. We report our findings in rank order and the top five markers had an NPL>2.5. The peak finding in these regions were D8S256 at 8q24, NPL 3.13; D18S878 at 18q22, NPL 2.90; D4S1629 at 4q32, NPL 2.80; D2S99 at 2p12, NPL 2.54; and D13S1493 at 13q12, NPL 2.53. No locus produced statistically significant evidence for linkage at the genome-wide level. The parent of origin effect was studied and consistent with our previous findings, evidence for a locus on 18q22 was predominantly from families wherein the father or paternal lineage was affected. There was evidence consistent with paternal imprinting at the loci on 13q12 and 1q41.     

Mapping of a second locus for familial hemiplegic migraine to 1q21–q23 and evidence of further heterogeneity

Familial hemiplegic migraine (FHM) is an autosomal dominant variety of migraine with aura. We previously mapped an FHM gene on the short arm of chromosome 19. Mutations in this gene, recently shown to be the α1 subunit of a P/Q-type voltage-dependent calcium channel, CACNL1A4, are involved in approximately 50% of unselected FHM families and in all families where migraine attacks are associated with permanent cerebellar ataxia. As a first step toward the identification of other FHM genes, we conducted a genetic linkage analysis in one large French pedigree and showed significant linkage to two microsatellite markers D1S2635 (Z_max: 3.33 at = 0.05) and D1S2705 (Z_max: 3.64 at = 0.05), establishing the existence of a second locus for FHM (FHM2) on chromosome 1q21–q23. Analysis of six additional FHM families favored linkage to this locus in two of them; linkage was excluded in the last four families, indicating further heterogeneity. Chromosome 1–linked families differ from the ones linked to chromosome 19, because penetrance in those families is much lower, and in some of their members, epileptic seizures occur during severe migraine attacks.     

Charcot–marie–tooth neuropathies: From clinical description to molecular genetics

Ninety-five families with Charcot-Marie-Tooth (CMT) neuropathies were studied clinically, electrophysiologically (MNCVs and EMGs), and by molecular genetics. Fifty-four families (56.8%) were type 1A mapped at 17p11.2-p12 and DNA duplication was present in 50 (92.6% of CMT1A families). One family with type 1B (1.1%) mapped at 1q22-q23 showed a point mutation of the myelin Po gene. Eighteen families (18.9%) were type CMT2 based on electrophysiological studies. Molecular genetics was not yet conclusive. Twenty CMT families were with X-linked dominant inheritance (CMTX1) (21.1%) mapped at Xq13.1 and connexin 32 (CX32) point mutations were present in 15 families (75%) (five nonsense mutations, eight missense mutations, two deletions). Two CMT families (2.1%) with X-linked recessive inheritance showed no point mutations of CX32 and their mapping was different from CMTX1, respectively at Xp22.2 for CMTX2 and at Xq26 for CMTX3.© 1995 John Wiley &Sons, Inc.     

Refined localization of dominant intermediate Charcot-Marie-Tooth neuropathy and exclusion of seven known candidate genes in the region

Charcot-Marie-Tooth (CMT) neuropathy is one of the most common hereditary disorders of the human peripheral nervous system. The CMT syndrome includes weakness and atrophy of distal muscles, high arched feet (pes cavus), depressed or absent deep tendon reflexes, and mild sensory loss. Dominant intermediate CMT (DI-CMT) neuropathy is a form of CMT with intermediate median motor nerve conduction velocities. We previously localized the DI-CMT locus to a 16.8-cM region on chromosome 19p12-p13.2. Extended haplotype analysis and clinical assessment of additional family members and a report of a second family linked to this locus has enabled us to narrow the candidate region to a 6-cM interval flanked by D19S558 and D19S432. Selection of positional candidate genes for screening was performed on the basis of neural expression and microarray analysis of Schwann cell differentiation in vivo. Seven candidate genes have been investigated. These include six genes localized in the original linkage interval and one in the newly refined region. They are excluded as a cause for DI-CMT neuropathy.     

Narrowing of the critical region in autosomal recessive spastic paraplegia linked to the SPG5 locus

Hereditary spastic paraplegias are neurodegenerative disorders characterized clinically by progressive spasticity of the lower limbs. They are inherited as autosomal dominant, autosomal recessive, and X-linked traits. Four Italian families with autosomal recessive pure spastic paraplegia are reported. We show evidence of linkage to the SPG5 locus on chromosome 8p and our data reduce the candidate interval for SPG5 to the11-cM interval spanned by D8S285 and D8S544. We also report the search for mutations in five genes located in the region and their exclusion as candidates for SPG5.     

Phenotype-genotype correlations in a CMT2B family with refined 3q13-q22 locus

OBJECTIVE: To perform genotype-phenotype correlation and genetic linkage analysis in a family with axonal Charcot-Marie-Tooth (CMT) syndrome and ulcero-mutilating features. BACKGROUND: CMT2B is a rare disorder belonging to the group of axonal CMT syndromes that is clinically characterized by marked distal muscle weakness and wasting as well as a high frequency of foot ulcers, infections, and amputations. So far only two families with this disorder have been described in which molecular genetic studies have shown evidence of autosomal dominant inheritance with linkage to chromosome 3q13-q22. METHODS: The authors report a large Austrian family presenting with the typical clinical features of CMT2B. Detailed clinical and electrophysiologic data were obtained in 15 at-risk individuals and DNA samples from 19 family members were collected for genetic linkage studies. RESULTS: Eight family members were definitely affected upon clinical and electrophysiologic examination and the majority revealed pronounced distal muscle wasting and weakness as well as prominent sensory abnormalities, which were frequently complicated by infections and amputations. Electrophysiologic studies showed normal or slightly to moderately slowed motor nerve conduction velocities, markedly reduced compound motor action potential amplitudes with chronodispersion, and absent or reduced amplitudes of sensory nerve action potentials. The molecular genetic study demonstrates linkage to chromosome 3q13-q22. Haplotype analysis in affected individuals indicates that the CMT2B locus is located between the flanking markers D3S1589 and D3S1549, representing a region of 10 cM. CONCLUSIONS: This family is the third CMT2B family reported so far and confirms the existence of the CMT2B locus on chromosome 3q13-q22, which is responsible for a clinically and electrophysiologically homogeneous disorder with prominent distal muscle weakness and wasting, and ulcero-mutilating features. Marked sensory disturbances and the high frequency of foot ulcers, infections, and amputations in our patients seem to be typical for CMT2B. Recombination events in affected individuals reduce the CMT2B candidate gene interval considerably from 25 to 10 cM.     

INF2 mutations in patients with a broad phenotypic spectrum of Charcot-Marie-Tooth disease and focal segmental glomerulosclerosis

Mutations in INF2 are associated with the complex symptoms of Charcot-Marie-Tooth disease (CMT) and focal segmental glomerulosclerosis (FSGS). To date, more than 100 and 30 genes have been reported to cause these disorders, respectively. This study aimed to identify INF2 mutations in Korean patients with CMT. This study was conducted with 743 Korean families with CMT who were negative for PMP22 duplication. In addition, a family with FSGS was included in this study. INF2 mutations were screened using whole exome sequencing (WES) and filtering processes. As the results, four pathogenic INF2 mutations were identified in families with different clinical phenotypes: p.L78P and p.L132P in families with symptoms of both CMT and FSGS; p.C104Y in a family with CMT; and p.R218Q in a family with FSGS. Moreover, different CMT types were observed in families with CMT symptoms: CMT1 in two families and Int-CMT in another family. Hearing loss was observed in two families with CMT1. Pathogenicity was predicted by in silico analyses, and considerable conformational changes were predicted in the mutant proteins. Two mutations (p.L78P and p.C104Y) were unreported, and three families showed de novo mutations that were putatively occurred from fathers. This study suggests that patients with INF2 mutations show a broad phenotypic spectrum: CMT1, CMT1 + FSGS, CMTDIE + FSGS, and FSGS. Therefore, the genotype-phenotype correlation may be more complex than previously recognized. We believe that this study expands the clinical spectrum of patients with INF2 mutations and will be helpful in the molecular diagnosis of CMT and FSGS.     

Charcot-Marie-Tooth disease (CMT): distinctive phenotypic and genotypic features in CMT type 2

Charcot-Marie-Tooth disease (CMT), or hereditary motor and sensory neuropathy (HMSN), includes two main subtypes of CMT1/HMSN I (demyelinating), and CMT2/HMSN II (axonal). Further heterogeneity has been demonstrated by genetic molecular studies, with at least four responsible genes for CMT1. As for CMT2, a mutation in the neurofilament-light (NF-L) gene has been identified in a single family, and other CMT2 loci have been mapped. We propose a clinical classification of the CMT2 phenotypes, and review the features of the identified CMT2 genotypes. The following main subtypes of CMT2 are considered in the phenotype classification: classical CMT2, the variants of CMT2 showing atypical features that may represent either variance in the classical CMT2 phenotype or separate entities; CMT2 plus, i.e. complex forms with involvement of additional neural structures. The recognized CMT2 genotypes include: CMT2A (mapped to chromosome 1p35-36); CMT2B (3q13-22); CMT2C (with vocal cord paresis); CMT2D (7p14); CMT2E, related to a mutation in the NF-L gene on chromosome 8p21; proximal CMT2, or HMSN P (3q13.1); CMT2 with MPZ mutations; autosomal recessive CMT2 (1q21.2-q21.3); agenesis of the corpus callosum with sensorimotor neuronopathy (15q13-q15); CMT2 X-linked with deafness and mental retardation (Xq24-q26). The identified genotypes may correspond to previously described clinical subtypes of CMT2. In particular, classical CMT2 presents in association with NF-L gene mutation, in the only CMT2 family with known gene mutation, and in CMT2A patients. However, the features of classical CMT2 have been paradoxically reported also in families with MPZ mutation, and conversely several CMT2 families are not linked to the known CMT2 loci. Further cloning of the CMT2 genes will ultimately shed light on the pathogenic mechanism(s) implicated in the process of axonal degeneration, shared by the different CMT2 genotypes.     

MFN2‐related genetic and clinical features in a cohort of Chinese CMT2 patients

Charcot‐Marie‐Tooth disease 2A (CMT2A), caused by mutations in the mitofusin 2 gene (MFN2), is the most common CMT2 subtype. The aim of our study is to assess the frequency and summarize the genetic and clinical characteristics of Chinese CMT2A patients. A total of 17 coding exons of MFN2 were detected by direct sequencing in 82 unrelated Chinese families diagnosed as CMT2. Clinical evaluations were analyzed among CMT2A patients. We identified 14 missense variants in 9 sporadic and 6 familial cases, including four novel mutations (T129A, S249F, Q367P, and Q674L), 4 known mutations (R94W, R94Q, T105M, C132Y, M376V and Q751X), and 4 rare missense variants (K120E, C217F, K307E and T356S). A total of 23 patients had early‐onset phenotype. Two patients had a CMTNS score of 0 to 10; 16 had a score of 11 to 20; and 7 had a score greater than 20. Five patients were confirmed a de novo origin. Six of 14 variants were located or closed to the GTPase domain. We report four novel mutations and four rare missense variants. MFN2 mutations account for 18% of CMT2 families in mainland China. The common characteristics of Chinese pedigree are early disease onset and moderate phenotypes.     

Partial Cosegregation of Familial Hemiplegic Migraine and a Benign Familial Infantile Epileptic Syndrome

: Purpose: We studied a large Dutch-Canadian family, in which two very rare hereditary paroxysmal neurologic disorders, familial hemiplegic migraine (FHM) and a “benign familial infantile epileptic syndrome” concur and partially cosegregate. FHM is a dominantly inherited subtype of migraine with attacks of hemiparesis, linked to chromosome 19p13 in 50% of the families tested. Recently mutations in a brain-specific P/Q-type Ca²⁺ channel α1 subunit gene (CACNLlA4) were identified in families with chromosome 19-linked FHM. The infantile epileptic syndrome resembles to two other dominantly inherited benign epilepsies occurring in the first year of life, benign familial neonatal convulsions (BFNC), assigned to chromosomes 20q13.2 and 8q, and benign infantile familial convulsions (BIFC), as yet unlinked. Methods: Linkage analysis was performed for the known locations of FHM and BFNC. The question whether the two conditions in this family can be caused by a single gene defect was addressed by additional linkage analysis. Results: We excluded linkage of the infantile convulsions to markers on chromosome 20q13.2, Sq, or 19p13. This indicates the existence of a third locus for benign familial convulsions in the first year of life. Linkage of FHM to these markers was not formally excluded but seems very unlikely. Statistical analysis of whether, in this family, both conditions are caused by a single gene defect was inconclusive. Conclusions: We describe a “benign familial infantile epileptic syndrome“ with attacks of FHM at a later age. Further genetic studies in this family may help to unravel the genetic basis of epilepsy or migraine or both.     

Mutilating neuropathic ulcerations in a chromosome 3q13-q22 linked Charcot-Marie-Tooth disease type 2B family.

BACKGROUND: Charcot-Marie-Tooth disease type 2 (CMT2) or hereditary motor and sensory neuropathy type II (HMSN II) is an inherited axonal neuropathy of the peripheral nervous system. Three autosomal dominant CMT2 loci have been located on chromosomes 1p35-p36 (CMT2A), 3q13-q22 (CMT2B), and 7p14 (CMT2D) indicating that CMT2 is a genetically heterogeneous disorder. METHODS: A CMT2 family was examined for linkage to the CMT2A, CMT2B, and CMT2D loci using short tandem repeat polymorphisms. RESULTS: Suggestive evidence for linkage to 3q13-q22 was found. Recombinations occurred with markers D3S1769 and D3S1267 indicating that the CMT2B locus is located distal to D3S1267 and resides in an interval of 25 cM. Some patients in this family have pronounced sensory disturbances leading to poorly healing ulcerations. CONCLUSIONS: These unusual sensory signs for CMT were also noted in the only other CMT2B family reported so far, suggesting a distinct clinical phenotype for CMT2B. Exclusion of the locus for hereditary sensory neuropathy type I (HSN I) on chromosome 9q22 indicates that HSN I with mild motor symptoms and CMT2 with prominent sensory abnormalities are not allelic.     

A novel locus for restless legs syndrome maps to chromosome 19p in an Irish pedigree

Restless legs syndrome (RLS) is a common, sleep-related movement disorder. The symptoms follow a circadian pattern, worsening in the evening or night, leading to sleep disruption and daytime somnolence. Familial forms of RLS have been described and usually display an autosomal dominant pattern of inheritance. To date, linkage analysis has identified nine RLS loci, but no specific causative gene has been reported. Association mapping has highlighted a further four genomic areas of interest. We have conducted a genome-wide linkage analysis in an Irish autosomal dominant RLS pedigree with 11 affected members. Significant linkage was found on chromosome 19p for a series of microsatellite markers, with a maximum two-point LOD score of 3.59 at θ = 0.0 for marker D19S878. Recombination events, identified by haplotype analysis, define a genetic region of 6.57 cM on chromosome 19p13.3, corresponding to an interval of 2.5 Mb. This study provides evidence of a novel RLS locus and provides further evidence that RLS is a genetically heterogenous disorder.