A novel locus for X-linked recessive CMT with deafness and optic neuropathy maps to Xq21.32-q24

The authors describe a Korean family with X-linked recessive Charcot-Marie-Tooth disease (CMT) having deafness and optic neuropathy. An X chromosome-wide linkage analysis identified a 15.2-cM candidate region flanked by DXS990 and DXS8067 on Xq21.32-q24 with the maximum lod score at DXS8077 (3.62, theta = 0.00). This locus does not overlap previously identified four loci for X-linked CMT, and the authors propose it as CMTX5.     

Linkage analyses between dominant X-linked Charcot-Marie-Tooth disease, and 15 Xq11–Xq21 microsatellites in a new large family: Three new markers are closely linked to the gene

X-linked dominant inheritance was suspected in a large family with Charcot-Marie-Tooth disease since no male to male transmission was observed, and since the sensory and motor neuropathy was more severe in males than in females. To test linkage to the dominant X-linked Charcot-Marie-Tooth disease (DCMTX) locus in Xq13, genotypes of 19 affected and 19 unaffected individuals from this family were determined for 4 microsatellite markers. Close linkage to mfd66 (DXS453) was found by bipoint analysis (Zmax = 4.8 at θ = 0.00). Multipoint analysis mapped the gene between the androgen receptor and DXYS1. In addition, linkage analysis performed with 11 microsatellite markers, derived from a high density map spanning 16 cM on Xq11–Xq21 revealed 3 new tightly linked loci: afm287zgl (DXS1216), afm261zh5 and afm207zg5 (DXS995). Multipoint analysis localized the DCMTX gene to a 7.5 cM interval between afm123xd4 (DXS988) and afm116xg1 (DXS986). Combined analysis with these new microsatellites provides a powerful tool for carrier detection because of their high informativity and the small genetic distance (< 10 cM) between the markers flanking the gene.     

X-linked recessive Charcot-Marie-Tooth neuropathy: clinical and genetic study.

We describe three families with X-linked recessive Charcot-Marie-Tooth (CMT) neuropathies. The disease phenotype in family 1 was characterized by infantile onset, weakness of lower legs, areflexia, pes cavus, and mental retardation (2 of 5 patients). The disease phenotype in families 2 and 3 was characterized by late onset, distal weakness, and normal intelligence. Hereditary spastic paraparesis was also present in the CMT patients of family 2. Thirty X-linked DNA markers were used for linkage studies. A maximum lod score of +3.48 was obtained by multipoint linkage analysis for the DXS16 locus mapped at Xp22.2 in family 1. In families 2 and 3, there was suggestion of linkage of Xq26 markers; the peak multipoint lod score for these 2 CMT families was 1.81, at DXS144. These results were suggestive of heterogeneity. The joint analysis including both regions (Xp22.2 and Xq26) provided evidence against homogeneity (chi 2 = 9.12, P less than 0.005).     

X-linked neuropathy: gene localization with DNA probes

We used probes for DNA polymorphisms on the X chromosome to study genetic linkage in four families with X-linked neuropathy. Despite clinical variability, all four families showed the same linkage pattern. We found evidence in each family of linkage to the marker DXYS1 on the proximal long arm of the X chromosome, as reported by others. We also found linkage to p58-1 (DXS14) on the proximal short arm. We found only loose linkage or nonlinkage to nine other markers located elsewhere on the chromosome. Our analysis places the gene defect for this disorder in the region of DXYS1 and p58-1, near the centromere of the X chromosome.     

Screening of dominantly inherited Charcot–Marie–Tooth neuropathies

Sixty-three families with dominantly inherited Charcot–Marie–Tooth (CMT) neuropathies including 730 subjects (total) from which 356 affected were studied clinically, electrophysiologically (MNCVs and EMGs), by genetic linkage, and screened for DNA duplication. Thirtyeight families (60.3%) were type 1A (demyelinating CMT mapped on chromosome 17). DNA duplication was present in 36 families (94.8% of CMT1A families). One CMT1A family (2.6%) showed no duplication but suggested genetic linkage with markers of chromosome 17. One CMT1A family (2.6%) revealed nonduplication in some affected members and duplication in other affected members. The disease in that family segregated with the same chromosome 17 markers regardless of duplication status. The other CMT families with dominant inheritance but without duplication included one family with CMT1B (demyelinating CMT mapped on chromosome 1) (1.6%), 14 families with CMT2 axonal neuropathy (22.2%), and 10 families with X-linked dominant CMT (15.9%). © 1993 John Wiley & Sons, Inc.     

Advances in the molecular diagnosis of Charcot-Marie-Tooth disease

Charcot-Marie-Tooth (CMT) disease or hereditary motor and sensory neuropathy is the most common inherited neuromuscular disorder affecting at least 1 in 2500. CMT disease is pathologically and genetically heterogeneous and is characterized by a variable age of onset, slowly progressive weakness and muscle atrophy, starting in the lower limbs and subsequently affecting the upper extremities. Symptoms are usually slowly progressive, especially for the classic and late-onset phenotypes, but can be rather severe in early-onset forms. CMT is grouped into demyelinating, axonal and intermediate forms, based on electrophysiological and pathological findings. The demyelinating types are characterized by severely reduced motor nerve conduction velocities (MNCVs) and mainly by myelin abnormalities. The axonal types are characterized by normal or slightly reduced MNCVs and mainly axonal abnormalities. The intermediate types are characterized by MNCVs between 25 m/s and 45 m/s and they have features of both demyelination and axonopathy. Inheritance can be autosomal dominant, X-linked, or autosomal recessive. Mutations in more than 30 genes have been associated with the different forms of CMT, leading to major advancements in molecular diagnostics of the disease, as well as in the understanding of pathogenetic mechanisms. This editorial aims to provide an account that is practicable and efficient on the current molecular diagnostic procedures for CMT, in correlation with the clinical, pathological and electrophysiological findings. The most frequent causative mutations of CMT will also be outlined.     

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.     

Localization of the gene for X-linked spinal muscular atrophy

We used probes for DNA polymorphisms on the X chromosome to study genetic linkage in seven families with X-linked adult-onset spinal muscular atrophy. We found significant linkage to the marker DXYS1 on the proximal X chromosome long arm and loose linkage or nonlinkage to markers elsewhere. Our analysis localizes the gene defect for this form of anterior horn cell disease.     

Multipoint linkage mapping of the Emery-Dreifuss muscular dystrophy gene.

The clinical features to establish the diagnosis of X-linked Emery-Dreifuss muscular dystrophy (EMD) were recently redefined at the European EMD workshop in Baarn 1991. These criteria were used to select families from the literature and two new families for linkage analysis with the DNA markers F9, DX52, DXS15, F8C and DXS115. Recombinations are observed with the DNA markers F9, DXS52 and DXS15. No recombinations were found with F8C and DXS115. Multipoint linkage analysis indicates with a maximum location score of 73.9 that the EMD locus maps very close to F8C.     

Novel mental retardation-epilepsy syndrome linked to Xp21.1-p11.4.

We evaluated a kindred with X-linked mental retardation and epilepsy. Seven affected males with mild to moderate mental retardation developed seizures (primarily generalized, tonic-clonic, and atonic) that began on average at 6.8 months of age (range, 4 to 14 months). These patients did not have a history of infantile spasms. There were no dysmorphic features. Other than mental retardation, the neurological examination was unremarkable, with exception of 2 affected subjects who had mild generalized rigidity and ataxia. We identified tight linkage to a group of markers on Xp21.1-p11.4. A maximum two-point LOD score of +3.83 at straight theta = 0 was obtained for markers DXS8090, DXS1069, DXS8102, and DXS8085. This locus spans 7.7cM between DXS1049 and DXS8054 and does not overlap the locus for X-linked West syndrome. The tetraspanin gene, implicated in nonspecific mental retardation, is mapped to this region. We sequenced the tetraspanin coding sequence in subjects with X-linked mental retardation and epilepsy and did not identify disease-specific mutations. The syndrome we describe, designated X-linked mental retardation and epilepsy, is clinically and genetically distinct from X-linked West syndrome and other X-linked mental retardation-epilepsy syndromes.     

Comparison between Clinical Disabilities and Electrophysiological Values in Charcot-Marie-Tooth 1A Patients with PMP22 Duplication

Background and Purpose

Charcot-Marie-Tooth disease (CMT) type 1A (CMT1A) is the demyelinating form of CMT that is significantly associated with PMP22 duplication. Some studies have found that the disease-related disabilities of these patients are correlated with their compound muscle action potentials (CMAPs), while others have suggested that they are related to the nerve conduction velocities. In the present study, we investigated the correlations between the disease-related disabilities and the electrophysiological values in a large cohort of Korean CMT1A patients.

Methods

We analyzed 167 CMT1A patients of Korean origin with PMP22 duplication using clinical and electrophysiological assessments, including the CMT neuropathy score and the functional disability scale.

Results

Clinical motor disabilities were significantly correlated with the CMAPs but not the motor nerve conduction velocities (MNCVs). Moreover, the observed sensory impairments matched the corresponding reductions in the sensory nerve action potentials (SNAPs) but not with slowing of the sensory nerve conduction velocities (SNCVs). In addition, CMAPs were strongly correlated with the disease duration but not with the age at onset. The terminal latency index did not differ between CMT1A patients and healthy controls.

Conclusions

In CMT1A patients, disease-related disabilities such as muscle wasting and sensory impairment were strongly correlated with CMAPs and SNAPs but not with the MNCVs or SNCVs. Therefore, we suggest that the clinical disabilities of CMT patients are determined by the extent of axonal dysfunction.     

Genetic mapping of "Lubag" (X-linked dystonia-parkinsonism) in a Filipino kindred to the pericentromeric region of the X chromosome.

"Lubag" is an X-linked disorder causing dystonia and parkinsonism that has only been described in families from the Philippines, principally from the island of Panay. We have established linkage between the disease phenotype "lubag" and DNA markers which span the Xp11.22-Xq21.3 region by using a large Filipino family with 8 affected men in three generations. These DNA markers define an interval of about 20 centimorgans in the pericentromeric region of the X chromosome as the most likely site of the disease locus XDPD (X-linked dystonia-parkinsonism). XDPD has a maximum multipoint log likelihood ratio score (Zmax) of about 4.6 over the interval from Xq12 to Xq21.31 (DXS159-DXYS1X). The co-occurrence of dystonia and parkinsonism in lubag and in other known disorders suggests there may be a common pathogenetic mechanism. Identification of the genetic defect in this family may provide an important clue toward understanding the pathogenesis and pathophysiology of both dystonia and parkinsonism.     

The gene for X-linked myotubular myopathy is located in an 8 Mb region at the border of Xq27.3 and Xq28

X-linked recessive myotubular myopathy (XLMTM) is a rare and severe neonatal neuromuscular disease characterized by muscle weakness, hypotonia, and respiratory problems. Here we report an extensive linkage analysis in two families with XLMTM. Using 18 markers in the Xq27-Xqter region we found a maximum two-point lod score of Z = 4.00 at Θ = 0.00 for the marker II-10 (DXS466). Three recombinations were detected between markers and the disease locus. At the distal side of Xq27.3 a recombination was present in between RNI (DXS369) and VK23b (DXS297), another in between VK23b (DXS297) and II-10 (DXS466), and at the proximal side of Xq28 a recombination in between U6.2 (DXS304) and Cpx67 (DXS134). Combining the results of both families we conclude that XLMTM is located in the 8 Mb (11 cM) region between VK23b (DXS297) and Cpx67 (DXS134).     

Assignment of the X-linked torsion dystonia gene to Xq21 by linkage analysis

We performed linkage analysis of X-linked torsion dystonia (XLTD) in 7 Filipino families, studying DNA from a total of 36 family members (9 obligate carrier females, and 18 affected and 9 unaffected males). Application of 21 informative X chromosomal DNA sequences allowed assignment of the XLTD locus to the proximal long arm of the X chromosome (Xq21). A maximum LOD score of 3.06 at [symbol: see text] = 0.0 was obtained with DXYS2, previously assigned to Xq21.3.     

Genetic Study of Demyelinating form of Autosomal-Recessive Charcot–Marie–Tooth Diseases in a Turkish Family

Charcot–Marie–Tooth (CMT) disease is a clinically and genetically heterogeneous group of inherited peripheral motor and sensory neuropathies characterized by distal muscle weakness atrophy predominantly in the lower extremities, diminished or absent deep tendon reflexes, distal sensory loss and skeletal deformities. Mode of inheritance could be either autosomal dominant, autosomal recessive, or X-linked. The autosomal-recessive subgroup of CMT (AR-CMT) neuropathies is heterogeneous as well. To date, nine demyelinating loci have been implicated in CMT4 and seven genes have been identified. It has been screened in this study for the presence of mutations in the coding region of GDAP1 and genetic linkage analyses of CMT4B1, CMT4B2, CMT4C, CMT4D, CMT4E, and CMT4F loci were tested in a Turkish family presenting recessively inherited form of CMT disease characterized by severe motor weakness. We did not find any mutations in GDAP1 and genetic linkage excluded for the six demyelinating genes loci (CMT4B1, CMT4B2, CMT4C, CMT4D, CMT4E, and CMT4F). Our findings indicate that another locus may be associated with AR-CMT disease.     

X-linked centronuclear myopathy: mapping the gene to Xq28.

The X-linked recessive centronuclear/myotubular myopathy (XLR-CNM/MTM1), a severe neonatal disorder characterized by generalized hypotonia, muscle weakness and primary asphyxia, has recently been mapped to Xq28. This report presents linkage analysis data of eight families with X-linked centronuclear myopathy. Four probes from the region Xq26-27 and five Xq28 probes were used to get more precise gene localization and marker order. St14 (DXS52), fully informative in all families, shows significant linkage to the CNM gene (z = 3.60; theta = 0.05), followed by DX13 (DXS15) (z = 2.03; theta = 0.06) and F8 (z = 1.86; theta = 0.00). Combination of the physical map derived by Kenwrick and Gitschier (1989) and our linkage data lead to the most probable order R/GCP-G6PD-(XLR-CNM-F8)-p767-St14-cpX67-++ +DX13 placing the CNM gene close to F8. The results of this study confirm strong linkage of the CNM gene to the region Xq28 and will permit carrier testing and prenatal diagnosis in CNM families. We conclude that the precise localization of this devastating disorder may be of great importance for genetic counselling in families at risk. The lack of information about gene frequency and mutation rate as well as the severity and burden of the disease point to the inevitable need for accurate clinical diagnosis.     

Linkage of Emery-Dreifuss muscular dystrophy to the red/green cone pigment (RGCP) genes, proximal to factor VIII.

Further DNA linkage studies on two previously described X-linked recessive Emery-Dreifuss muscular dystrophy (EMD) families are reported, which refine the localization of the gene responsible for EMD. Two recombination events indicate that the most likely localization for the EMD gene lies in the interval between DXS15/DXS52 and F8C. A maximum LOD score of 3.44 at theta = 0 is obtained for EMD vs the red and green cone pigment genes (RCP and GCP). Our data provide additional support for one of the two proposed orientations of genes and markers distal to DXS15/DXS52, with respect to the telomere. Given this favoured orientation, our data best fit a localization of EMD to within a 2 megabase (Mb) interval between DXS15/DXS52 and F8C.     

Dominantly inherited peripheral neuropathies

Since 1886, the year that Charcot and Marie and Tooth described a genetic "peroneal muscular atrophy syndrome," electrophysiological and histological studies of the peripheral nervous system have greatly aided the characterization of this syndrome, which falls among the hereditary sensory-motor neuropathies. Two principal forms of Charcot-Marie-Tooth (CMT) disease have been distinguished: CMT 1, corresponding to a demyelinating type, and CMT 2, corresponding to an axonal type. The modes of transmission of these types are variable, recessive or dominant, autosomal, or X-linked. Our discussion here is confined to the dominant forms. In recent years, advances in molecular biology have greatly modified the approach to CMT disease and related neuropathies (such as hereditary neuropathy with liability to pressure palsies). With increased knowledge of responsible gene mutations and several other loci identified by linkage studies, our understanding of the pathophysiology of these neuropathies is increasing; however, with greater understanding, the classification of these disorders is becoming more complex. In this review we present and discuss the currently characterized subtypes, with emphasis on their known histological aspects. While nerve biopsy has lost its diagnostic importance in certain forms of the disease, such as CMT 1A, CMT 1B, and X-linked CMT (CMT X), it remains important for better characterizing the lesions of CMT 2 and forms of genetic peroneal atrophy in which DNA study is unrevealing.     

X连锁腓骨肌萎缩症Cx32基因的突变、临床和电生理特点

目的 分析X连锁腓骨肌萎缩症（CMTX）患者Cx32基凶的突变及其临床表现和电生理特点、方法应用多聚酶链反应一单链构象多态性分析结合DNA直接测序的方法,对24例无周围髓鞘蛋白（PMP）22基因大片段重复突变,家系中无男传男的腓骨肌萎缩症（CMT）先证者进行Cx32基因的突变分析;对先证者及其家系内患者进行临床和电生理检查。结果 在6个X连锁遗传家系和1例散发患者中发现了7个不同的Cx32基因突变,其中4个家系临床分型为CMTI型,2个家系为CMT中间型,散发病例为CMT1型检测到有Cx32基因突变的家系成员共38例,其巾男性20例,全部为CMTX患者;女性18例,其中6例为CMTX患者,12例为无临床症状的携带者;26例患者均为周围神经轻、中度受累。结论 CMTX的遗传方式可为X连锁显性、X连锁隐性遗传,也可为散发。根据临床和电生理特点分为CMTI型或CMT中间型,多为周围神经轻、中度受累,男性患者的症状通常较女性重。在没有检测到PMP22基因大片段重复突变和无男传男的CMT家系中应首先进行Cx32基因突变分析。