Identification of a new autosomal dominant limb-girdle muscular dystrophy locus on chromosome 7.

We report the identification of a new locus for autosomal dominant limb-girdle muscular dystrophy (LGMD1) on 7q. Two of five families (1047 and 1701) demonstrate evidence in favor of linkage to this region. The maximum two-point LOD score for family 1047 was 3.76 for D7S427, and that for family 1701 was 2.63 for D7S3058. Flanking markers place the LGMD1 locus between D7S2423 and D7S427, with multipoint analysis slightly favoring the 9-cM interval spanned by D7S2546 and D7S2423. Three of five families appear to be unlinked to this new locus on chromosome 7, thus establishing further heterogeneity within the LGMD1 diagnostic classification.     

A gene for limb-girdle muscular dystrophy maps to chromosome 15 by linkage

Limb-girdle muscular dystrophy (LGMD) is inherited as a monogenic, autosomal recessive trait. A genetically homogeneous group of families from the Isle of La Réunion, comprising individuals at high risk for this disorder, was systematically analysed using a panel of 85 polymorphic markers spanning approximately 30% of the human genome. Linkage was detected between the LGMD gene and the marker D15S25, uncovered with the probe pTHH114 and restriction enzyme RsaI (lod score = 5.52 at a 0 = 0.0), localising this gene onto chromosome 15. Such a lod score corresponds to odds of 3.3 x 105 in favor of linkage versus absence of linkage. Additional families from other populations will need to be examined before the role of this newly identified locus can be understood.     

Molecular genetic evidence of clinical heterogeneity in Fukuyama-type congenital muscular dystrophy

Fukuyama-type congenital muscular dystrophy (FCMD) is an autosomal recessive severe muscular dystrophy associated with brain malformation. The gene responsible for FCMD was mapped to chromosome 9q31, a region in which convincing evidence of strong linkage disequilibrium between FCMD and mfd220 (D9S306) was recently found. FCMD is also characterized clinically by a peak motor function which, at best, allows patients to sit unassisted or slide on the buttocks. However, a small fraction of patients acquire the capacity to walk unassisted. Whether such ambulant cases belong to the FCMD spectrum or to a different disease entity has been a topic of considerable debate. We performed linkage analysis for ten families with ambulant cases using DNA markers flanking the FCMD locus. The mfd220 locus yielded a significant lod score of 3.09 for ambulant FCMD. We also found evidence for linkage disequilibrium between ambulant FCMD and mfd220. We further conducted haplotype analysis in FCMD siblings with different phenotypes, one of whom was ambulant while the other was not. The results indicate that the FCMD siblings share exactly the same haplotype at nine marker loci spanning 23.3 cM surrounding the FCMD locus. On the basis of these results, we conclude that, genetically, ambulant cases are, in fact, part of the FCMD spectrum. Received: 28 June 1996     

Linkage-disequilibrium mapping narrows the Fukuyama-type congenital muscular dystrophy (FCMD) candidate region to <100 kb.

Fukuyama-type congenital muscular dystrophy (FCMD), the second most common form of muscular dystrophy in Japan, is an autosomal recessive severe muscular dystrophy associated with brain anomalies. After our initial mapping of the FCMD locus to chromosome 9q31-33, we have further defined the locus within a approximately 5-cM region between D9S127 and D9S2111 and have found linkage disequilibrium between FCMD and D9S306 in this candidate region on 9q31. The high prevalence of FCMD among the Japanese, who are a relatively isolated population, provides an opportunity to utilize linkage-disequilibrium mapping. We developed three new microsatellites, near D9S306, from the FCMD YAC contig, determined their positions on YACs, and performed linkage-disequilibrium mapping with these markers and other newly published loci. The maximum value of p(excess), which represents the strength of linkage disequilibrium, was obtained at D9S2107; and this value showed a relatively steady rise and fall across the region that is likely to contain FCMD. Distances between FCMD and each marker were presumed to be approximately 1 Mb, approximately 350 kb, approximately 140 kb, approximately 20 kb, approximately 280 kb, approximately 450 kb, and approximately 740 kb for D9S306, A107XF9, D9S2105, D9S2107, D9S172, D9S299, and D9S2109, respectively. Haplotype analysis using the three closest markers D9S2105, D9S2107, and D9S172 indicated that most FCMD-bearing chromosomes are derived from a single ancestral founder and suggested that these markers can be used for the diagnosis of sporadic FCMD. Thus, the FCMD gene is most likely to lie within a region of <100 kb containing D9S2107.     

Founder-haplotype analysis in Fukuyama-type congenital muscular dystrophy (FCMD)

Fukuyama-type congenital muscular dystrophy (FCMD) is an autosomal recessive, severe muscular dystrophy associated with brain anomalies. After our initial mapping of the FCMD locus to 9q31–33, we performed linkage disequilibrium analysis, which led us to suspect that the FCMD gene lay within a region of less than 100 kb containing D9S2107. In the present study, we developed two new microsatellites (D9S2170 and D9S2171) in close vicinity to D9S2107 and examined haplotypes of FCMD chromosomes by using four markers (cen-D9S2105-D9S2170-D9S2171-D9S2107-tel). As 82% of the FCMD chromosomes that we examined shared the founder haplotype (138–192–147–183) and 94% of the FCMD patients in our panel carried founder haplotypes on one or both chromosomes, the data supported the hypothesis of a single founder of this disease in the Japanese population. Eight haplotypes different from the founder’s were observed in FCMD chromosomes, indicating that eight different FCMD mutations in addition to the founder’s have occurred in Japan. Moreover, we have detected several historical recombinations that have disrupted the founder haplotype at D9S2105 or D9S2170 and conclude that the FCMD gene is probably located just centromeric to D9S2170. Received: 16 May 1998 / Accepted: 10 June 1998     

Limb-girdle muscular dystrophy type 2H associated with mutation in TRIM32, a putative E3-ubiquitin-ligase gene

Limb-girdle muscular dystrophy type 2H (LGMD2H) is a mild autosomal recessive myopathy that was first described in the Manitoba Hutterite population. Previous studies in our laboratory mapped the causative gene for this disease to a 6.5-Mb region in chromosomal region 9q31-33, flanked by D9S302 and D9S1850. We have now used additional families and a panel of 26 microsatellite markers to construct haplotypes. Twelve recombination events that reduced the size of the candidate region to 560 kb were identified or inferred. This region is flanked by D9S1126 and D9S737 and contains at least four genes. Exons of these genes were sequenced in one affected individual, and four sequence variations were identified. The families included in our study and 100 control individuals were tested for these variations. On the basis of our results, the mutation in the tripartite-motif-containing gene (TRIM32) that replaces aspartate with asparagine at position 487 appears to be the causative mutation of LGMD2H. All affected individuals were found to be homozygous for D487N, and this mutation was not found in any of the controls. This mutation occurs in an NHL (named after the proteins NCL1, HT2A, and LIN-41) domain at a position that is highly conserved. NHL domains are known to be involved in protein-protein interactions. Although the function of TRIM32 is unknown, current knowledge of the domain structure of this protein suggests that it may be an E3-ubiquitin ligase. If proven, this represents a new pathogenic mechanism leading to muscular dystrophy.     

Multiple independent molecular etiology for limb-girdle muscular dystrophy type 2A patients from various geographical origins.

Limb-girdle muscular dystrophies (LGMDs) are a group of neuromuscular diseases presenting great clinical heterogeneity. Mutations in CANP3, the gene encoding muscle-specific calpain, were used to identify this gene as the genetic site responsible for autosomal recessive LGMD type 2A (LGMD2A; MIM 253600). Analyses of the segregation of markers flanking the LGMD2A locus and a search for CANP3 mutations were performed for 21 LGMD2 pedigrees from various origins. In addition to the 16 mutations described previously, we report 19 novel mutations. These data indicate that muscular dystrophy caused by mutations in CANP3 are found in patients from all countries examined so far and further support the wide heterogeneity of molecular defects in this rare disease.     

Limb-girdle muscular dystrophy and Miyoshi myopathy in an aboriginal Canadian kindred map to LGMD2B and segregate with the same haplotype.

We report the results of our investigations of a large, inbred, aboriginal Canadian kindred with nine muscular dystrophy patients. The ancestry of all but two of the carrier parents could be traced to a founder couple, seven generations back. Seven patients presented with proximal myopathy consistent with limb girdle-type muscular dystrophy (LGMD), whereas two patients manifested predominantly distal wasting and weakness consistent with Miyoshi myopathy (distal autosomal recessive muscular dystrophy) (MM). Age at onset of symptoms, degree of creatine kinase elevation, and muscle histology were similar in both phenotypes. Segregation of LGMD/MM is consistent with autosomal recessive inheritance, and the putative locus is significantly linked (LOD scores >3.0) to six marker loci that span the region of the LGMD2B locus on chromosome 2p. Our initial hypothesis that the affected patients would all be homozygous by descent for microsatellite markers surrounding the disease locus was rejected. Rather, two different core haplotypes, encompassing a 4-cM region spanned by D2S291-D2S145-D2S286, segregated with the disease, indicating that there are two mutant alleles of independent origin in this kindred. There was no association, however, between the two different haplotypes and clinical variability; they do not distinguish between the LGMD and MM phenotypes. Thus, we conclude that LGMD and MM in our population are caused by the same mutation in LGMD2B and that additional factors, both genetic and nongenetic, must contribute to the clinical phenotype.     

Assignment of the muscle-eye-brain disease gene to 1p32-p34 by linkage analysis and homozygosity mapping.

Muscle-eye-brain disease (MEB) is an autosomal recessive disease of unknown etiology characterized by severe mental retardation, ocular abnormalities, congenital muscular dystrophy, and a polymicrogyria-pachygyria-type neuronal migration disorder of the brain. A similar combination of muscle and brain involvement is also seen in Walker-Warburg syndrome (WWS) and Fukuyama congenital muscular dystrophy (FCMD). Whereas the gene underlying FCMD has been mapped and cloned, the genetic location of the WWS gene is still unknown. Here we report the assignment of the MEB gene to chromosome 1p32-p34 by linkage analysis and homozygosity mapping in eight families with 12 affected individuals. After a genomewide search for linkage in four affected sib pairs had pinpointed the assignment to 1p, the MEB locus was more precisely assigned to a 9-cM interval flanked by markers D1S200 proximally and D1S211 distally. Multipoint linkage analysis gave a maximum LOD score of 6.17 at locus D1S2677. These findings provide a starting point for the positional cloning of the disease gene, which may play an important role in muscle function and brain development. It also provides an opportunity to test other congenital muscular dystrophy phenotypes, in particular WWS, for linkage to the same locus.     

Genetic localization of a newly recognized autosomal dominant limb-girdle muscular dystrophy with cardiac involvement (LGMD1B) to chromosome 1q11-21.

Limb-girdle muscular dystrophy (LGMD) constitutes a clinically and genetically heterogeneous group of myogenic disorders with a limb-girdle distribution of weakness. One autosomal dominant family, LGMD1A, has been linked to chromosome 5q, whereas in other autosomal dominant families linkage to this chromosome has been excluded. We studied 58 members of three families with a newly recognized autosomal dominantly inherited LGMD with cardiac involvement. A search with highly polymorphic microsatellite markers was carried out. The gene for this newly recognized dominant form of LGMD was located on chromosome 1q11-21, with a combined maximum two-point LOD score >12 at theta = 0.     

Refined Mapping of a Gene Responsible for Fukuyama-Type Congenital Muscular Dystrophy: Evidence for Strong Linkage Disequilibrium

Fukuyama-type congenital muscular dystrophy (FCMD), the second most common form of childhood muscular dystrophy in Japan, is an autosomal recessive severe muscular dystrophy associated with an anomaly of the brain. After our initial mapping of the FCMD locus to chromosome 9q31-33, we further defined the locus within a region of ~5 cM between loci D9S127 and CA246, by homozygosity mapping in patients born to consanguineous marriages and by recombination analyses in other families. We also found evidence for strong linkage disequilibrium between FCMD and a polymorphic microsatellite marker, mfd220, which showed no recombination and a lod score of (Z) 17.49. A “111-bp” allele for the mfd220 locus was observed in 22 (34%) of 64 FCMD chromosomes, but it was present in only 1 of 120 normal chromosomes. This allelic association with FCMD was highly significant (χ² =50.7; P<.0001). Hence, we suspect that the FCMD gene could lie within a few hundred kilobases of the mfd220 locus.     

Assignment of the tibial muscular dystrophy locus to chromosome 2q31.

Tibial muscular dystrophy (TMD) is a rare autosomal dominant distal myopathy with late adult onset. The phenotype is relatively mild: muscle weakness manifests in the patient's early 40s and remains confined to the tibial anterior muscles. Histopathological changes in muscle are compatible with muscular dystrophy, with the exception that rimmed vacuoles are a rather common finding. We performed a genomewide scan, with 279 highly polymorphic Cooperative Human Linkage Center microsatellite markers, on 11 affected individuals of one Finnish TMD family. The only evidence for linkage emerged from markers in a 43-cM region on chromosome 2q. In further linkage analyses, which included three other Finnish TMD families and which used a denser set of markers, a maximum two-point LOD score of 10.14 (recombination fraction of .05) was obtained with marker D2S364. Multipoint likelihood calculations, combined with the haplotype and recombination analyses, restricted the TMD locus to an approximately 1-cM critical chromosomal region without any evidence of heterogeneity. Since all the affecteds share one core haplotype, the dominance of one ancestor mutation is obvious in the Finnish TMD families. The disease locus that was found represents a novel muscular dystrophy locus, providing evidence for the involvement of one additional gene in the distal myopathy group of muscle disorders.     

A new locus for autosomal recessive hereditary spastic paraplegia maps to chromosome 16q24.3.

Hereditary spastic paraplegia is a genetically and phenotypically heterogeneous disorder. Both pure and complicated forms have been described, with autosomal dominant, autosomal recessive, and X-linked inheritance. Various loci (SPG1-SPG6) associated with this disorder have been mapped. Here, we report linkage analysis of a large consanguineous family affected with autosomal recessive spastic paraplegia with age at onset of 25-42 years. Linkage analysis of this family excluded all previously described spastic paraplegia loci. A genomewide linkage analysis showed evidence of linkage to chromosome 16q24.3, with markers D16S413 (maximum LOD score 3.37 at recombination fraction [theta] of .00) and D16S303 (maximum LOD score 3.74 at straight theta=.00). Multipoint analysis localized the disease gene in the most telomeric region, with a LOD score of 4.2. These data indicate the presence of a new locus linked to pure recessive spastic paraplegia, on chromosome 16q24.3, within a candidate region of 6 cM.     

Localization of the gene for autosomal recessive congenital hereditary endothelial dystrophy (CHED2) to chromosome 20 by homozygosity mapping.

Congenital hereditary endothelial dystrophy (CHED) is a corneal disorder that presents with diffuse bilateral corneal clouding. Vision may be severely impaired, and many patients require corneal transplantation. Both autosomal dominant (AD) and autosomal recessive (AR) forms of the disorder have been described. The gene responsible for AD CHED (HGMW-approved symbol CHED1) has been mapped to the pericentromeric region of chromosome 20. Investigating a large, consanguineous Irish pedigree with autosomal recessive CHED, we have previously excluded linkage to this AD CHED locus. We now describe a genome-wide search using homozygosity mapping and DNA pooling. Evidence of linkage to chromosome 20p was demonstrated with a maximum lod score of 9.30 at a recombination fraction of 0.0 using microsatellite marker D20S482. A region of homozygosity in all affected individuals was identified, narrowing the disease gene locus to an 8-cM region flanked by markers D20S113 and D20S882. This AR CHED (HGMW-approved symbol CHED2) disease gene locus is physically and genetically distinct from the AD CHED locus.     

Confirmation of genetic heterogeneity in limb-girdle muscular dystrophy: Linkage of an autosomal dominant form to chromosome 5q

Limb-girdle muscular dystrophy (LGMD) is a clinically and genetically heterogenous group of disorders, with both recessive and dominant forms reported. Recently, a series of recessive LGMD families were linked to chromosome 15q. We report herein the results of our linkage studies in a previously reported large autosomal dominant family. The LGMD gene in this family was localized to chromosome 5q22.3-31.3 by using a series of CA(n) microsatellite repeat markers. Linkage to 15q was excluded. These findings confirm genetic heterogeneity in this clinically diverse syndrome.     

Linkage of recessive Robinow syndrome to a 4 cM interval on chromosome 9q22

Autosomal recessive Robinow syndrome is a form of mesomelic dwarfism with multiple rib and vertebral anomalies. Using autozygosity mapping we have identified a genetic locus (RBNW1) for this syndrome at chromosome 9q22 in seven consanguineous families from Oman. Our results indicate that the gene lies within a 4 cM region between markers D9S1836 and D9S1803 (maximum multipoint LOD score 12.3). In addition, we have analysed two non-Omani families with autosomal recessive Robinow and found no genetic heterogeneity.     

An autosomal recessive nonsyndromic-hearing-loss locus identified by DNA pooling using two inbred Bedouin kindreds.

Autosomal recessive nonsyndromic hearing loss (ARNSHL) is the most common form of severe inherited childhood deafness. We present the linkage analysis of two inbred Bedouin kindreds from Israel that are affected with ARNSHL. A rapid genomewide screen for markers linked to the disease was performed by using pooled DNA samples. This screen revealed evidence for linkage with markers D9S922 and D9S301 on chromosome 9q. Genotyping of individuals from both kindreds confirmed linkage to chromosome 9q and a maximum combined LOD score of 26.2 (recombination fraction [theta] .025) with marker D9S927. The disease locus was mapped to a 1.6-cM region of chromosome 9ql3-q2l, between markers D9S15 and D9S927. The disease segregates with a common haplotype in the two kindreds, at markers D9S927, D9S175, and D9S284 in the linked interval, supporting the hypothesis that both kindreds inherited the deafness gene from a common ancestor. Although this nonsyndromic-hearing-loss (NSHL) locus maps to the same cytogenetic interval as DFNB7, it does not overlap the currently defined DFNB7 interval and may represent (1) a novel form of NSHL in close proximity to DFNB7 or (2) a relocalization of the DFNB7 interval to a region telomeric to its reported location. This study further demonstrates that DNA pooling is an effective means of quickly identifying regions of linkage in inbred families with heterogeneous autosomal recessive disorders.     

Localization of a gene for familial hemophagocytic lymphohistiocytosis at chromosome 9q21.3-22 by homozygosity mapping.

Familial hemophagocytic lymphohistiocytosis (FHL), also known as familial erythrophagocytic lymphohistiocytosis and familial histiocytic reticulosis, is a rare autosomal recessive disorder of early childhood characterized by excessive immune activation. Linkage of the disease gene to an approximately 7.8-cM region between markers D9S1867 and D9S1790 at 9q21.3-22 was identified by homozygosity mapping in four inbred FHL families of Pakistani descent with a combined maximum multipoint LOD score of 6.05. This is the first genetic locus to be described in FHL. However, homozygosity by descent across this interval could not be demonstrated in an additional affected kindred of Arab origin, whose maximum multipoint LOD score was -0.12. The combined sample revealed significant evidence for linkage to 9q markers (LOD score with heterogeneity, 5.00). Identification of the gene(s) involved in the pathogenesis of FHL will contribute to an understanding of the control of T-lymphocyte and macrophage activation, which is central to homeostasis in the immune system.     

A third novel locus for primary autosomal recessive microcephaly maps to chromosome 9q34

Primary autosomal recessive microcephaly is a clinical diagnosis of exclusion in an individual with a head circumference >/=4 SDs below the expected age-and-sex mean. There is associated moderate mental retardation, and neuroimaging shows a small but structurally normal cerebral cortex. The inheritance pattern in the majority of cases is considered to be autosomal recessive. Although genetic heterogeneity for this clinical phenotype had been expected, this has only recently been demonstrated, with the mapping of two loci for autosomal recessive primary microcephaly: MCPH1 at 8p and MCPH2 at 19q. We have studied a large multiaffected consanguineous pedigree, using a whole-genome search, and have identified a third locus, MCPH3 at 9q34. The minimal critical region is approximately 12 cM, being defined by the markers cen-D9S1872-D9S159-tel, with a maximum two-point LOD score of 3.76 (recombination fraction 0) observed for the marker D9S290.