Development of a microsatellite genetic map spanning 5q31-q33 and subsequent placement of the LGMD1A locus between D5S178 and IL9

The Role of Z-disc Proteins in Myopathy and Cardiomyopathy

The Z-disc acts as a protein-rich structure to tether thin filament in the contractile units, the sarcomeres, of striated muscle cells. Proteins found in the Z-disc are integral for maintaining the architecture of the sarcomere. They also enable it to function as a (bio-mechanical) signalling hub. Numerous proteins interact in the Z-disc to facilitate force transduction and intracellular signalling in both cardiac and skeletal muscle. This review will focus on six key Z-disc proteins: α-actinin 2, filamin C, myopalladin, myotilin, telethonin and Z-disc alternatively spliced PDZ-motif (ZASP), which have all been linked to myopathies and cardiomyopathies. We will summarise pathogenic variants identified in the six genes coding for these proteins and look at their involvement in myopathy and cardiomyopathy. Listing the Minor Allele Frequency (MAF) of these variants in the Genome Aggregation Database (GnomAD) version 3.1 will help to critically re-evaluate pathogenicity based on variant frequency in normal population cohorts.

Prevalence, pathological mechanisms, and genetic basis of limb-girdle muscular dystrophies: A review

Limb-girdle muscular dystrophies (LGMDs) are a highly heterogeneous group of neuromuscular disorders that are associated with weakness and wasting of muscles in legs and arms. Signs and symptoms may begin at any age and usually worsen by time. LGMDs are autosomal disorders with different types and their prevalence is not the same in different areas. New technologies such as next-generation sequencing can accelerate their diagnosis. Several important pathological mechanisms that are involved in the pathology of the LGMD include abnormalities in dystrophin-glycoprotein complex, the sarcomere, glycosylation of dystroglycan, vesicle and molecular trafficking, signal transduction pathways, and nuclear functions. Here, we provide a comprehensive review that integrates LGMD clinical manifestations, prevalence, and some pathological mechanisms involved in LGMDs.

The Classification, Natural History and Treatment of the Limb Girdle Muscular Dystrophies

Over sixty years ago John Walton and Frederick Nattrass defined limb girdle muscular dystrophy (LGMD) as a separate entity from the X-linked dystrophinopathies such as Duchenne and Becker muscular dystrophies. LGMD is a highly heterogeneous group of very rare neuromuscular disorders whose common factor is their autosomal inheritance. Sixty years later, with the development of increasingly advanced molecular genetic investigations, a more precise classification and understanding of the pathogenesis is possible.To date, over 30 distinct subtypes of LGMD have been identified, most of them inherited in an autosomal recessive fashion. There are significant differences in the frequency of subtypes of LGMD between different ethnic populations, providing evidence of founder mutations. Clinically there is phenotypic heterogeneity between subtypes of LGMD with varying severity and age of onset of symptoms. The first natural history studies into subtypes of LGMD are in process, but large scale longitudinal data have been lacking due to the rare nature of these diseases. Following natural history data collection, the next challenge is to develop more effective, disease specific treatments. Current management is focussed on symptomatic and supportive treatments. Advances in the application of new omics technologies and the generation of large-scale biomedical data will help to better understand disease mechanisms in LGMD and should ultimately help to accelerate the development of novel and more effective therapeutic approaches.

Clinical and myopathological evaluation of early- and late-onset subtypes of myofibrillar myopathy

Myofibrillar myopathies (MFM) are a group of disorders associated with mutations in DES, CRYAB, MYOT, ZASP, FLNC, or BAG3 genes and characterized by disintegration of myofibrils and accumulation of degradation products into intracellular inclusions. We retrospectively evaluated 53 MFM patients from 35 Spanish families. Studies included neurologic exam, muscle imaging, light and electron microscopic analysis of muscle biopsy, respiratory function testing and cardiologic work-up. Search for pathogenic mutations was accomplished by sequencing of coding regions of the six genes known to cause MFM. Mutations in MYOT were the predominant cause of MFM in Spain affecting 18 of 35 families, followed by DES in 11 and ZASP in 3; in 3 families the cause of MFM remains undetermined. Comparative analysis of DES, MYOT and ZASP associated phenotypes demonstrates substantial phenotypic distinctions that should be considered in studies of disease pathogenesis, for optimization of subtype-specific treatments and management, and directing molecular analysis.

Generalized muscle pseudo-hypertrophy and stiffness associated with the myotilin Ser55Phe mutation: a novel myotilinopathy phenotype?

Myotilinopathies are a group of muscle disorders caused by mutations in the MYOT gene. It was first described in two families suffering from limb girdle muscle dystrophy type 1 (LGMD 1A), and later identified in a subset of dominant or sporadic patients suffering from myofibrillar myopathy, as well as in a family with spheroid body myopathy. Disease phenotypes associated with MYOT mutations are clinically heterogeneous and include pure LGMD forms as well as late-onset distal myopathies. We report here on a 53-year-old male suffering from a unique clinical profile characterized by generalized symmetrical increase in muscle bulk leading to a Herculean appearance. Muscle weakness and stiffness in the lower extremities were the patient's main complaints. Muscle MRI showed extensive fatty infiltration in the thigh and leg muscles and a muscle biopsy showed a myofibrillar myopathy with prominent protein aggregates. Gene sequencing revealed a Ser55Phe missense mutation in the myotilin gene. The mutation was identified in his older brother, who presented a mild hypertrophic appearance and had a myopathic pattern in EMG, despite not presenting any of the complaints of the proband and having normal muscle strength. This finding, and his deceased father and paternal aunt's similar gait disorders, suggest that this is in fact a new autosomal dominant kindred. The present observations further expand the spectrum of clinical manifestations associated with mutations in the myotilin gene.

Myotilinopathy: refining the clinical and myopathological phenotype

Mutations in myotilin gene (MYOT) have been associated with variable syndromes including limb girdle muscular dystrophy type 1A (LGMD1A) and a subgroup of myofibrillar myopathy (MFM/MYOT). We studied six Spanish patients from three unrelated kindreds and seven patients without family history. Three previously reported and two novel disease-associated MYOT mutations were identified in this group of patients. The disease is characterized by the onset at the age of 42-77 years with muscle weakness initially in distal or proximal leg muscles, eventually spreading to other muscle groups of the lower and upper extremities. Associated signs of cardiomyopathy, respiratory failure and peripheral neuropathy are present in a fraction of patients. Myopathological features of focal myofibrillar destruction resulting in intracytoplasmic deposits, strongly immunoreactive to myotilin, multiple rimmed and centrally or subsarcolemmally located non-rimmed vacuoles and streaming Z-lines, were observed in each patient studied. The Spanish cohort, the largest group of patients studied so far, shares phenotypic features with both LGMD1A and MFM/MYOT variants thus establishing a continuum of phenotypic manifestations characteristic of myotilinopathy, an emerging neuromuscular disorder.

Klinik und Genetik der Gliederg�rteldystrophien

Limb girdle muscular dystrophies (LGMDs) are a genetically heterogeneous group of primary myopathies involving progressive weakness and wasting of the muscles in the hip and shoulder girdles, with distal spread to the bulbar or respiratory musculature in rare cases. Depending on the mode of genetic transmission, six autosomal dominant forms (LGMD1A-F, 10-25%) and ten autosomal recessive forms (LGMD2A-J, 75-90%) are currently known. The prevalence of LGMDs is 0.8/100,000. These conditions are caused by mutations in genes encoding for myotilin (5q31, LGMD1A), lamin A/C (1q11-q21.2, LGMD1B), caveolin-3 (3p25, LGMD1C), unknown proteins (7q, LGMD1D, 6q23, LGMD1E, 7q32.1-32.2., LGMD1F), calpain-3 (15q15.1-21.1, LGMD2A), dysferlin (2p13.3-13.1, LGMD2B), gamma-sarcoglycan (13q12, LGMD2C), alpha-sarcoglycan, also known as adhalin (17q12-q21.3, LGMD2D), beta-sarcoglycan (4q12, LGMD2E), delta-sarcoglycan (5q33-q34, LGMD2F), telethonin (17q11-q12, LGMD2G), E3-ubiquitin ligase (9q31-q34.1, LGMD2H), fukutin-related protein (19q13.3, LGMD2I), and titin (2q31, LGMD2J). Cardiac involvement has been described for LGMD1B-E, LGMD2C-G, and LGMD2I. The time of onset varies between early childhood and middle age. There is no male or female preponderance. Disease progression and life expectancy vary widely, even among different members of the same family. The diagnosis is based primarily on DNA analysis. The history, clinical neurological examinations, blood chemistry investigations, electromyography, and muscle biopsy also provide information that is helpful for the diagnosis. No causal therapy is currently available.

Autosomal dominant limb-girdle muscular dystrophy with ankle joint contracture

We herein describe a Japanese family suffering from autosomal dominant limb-girdle muscular dystrophy showing a later onset and a predilection for males. All patients developed a plantar flexion contracture of the ankles when no distal muscular weakness was evident. The serum creatine kinase activity was remarkably elevated to 55 times the normal value. These clinical features suggest a novel phenotype.

A second locus for autosomal dominant myopathy with proximal muscle weakness and early respiratory muscle involvement: a likely chromosomal locus on 2q21

We recently mapped a locus for a new variant of autosomal dominant myopathy (Swedish families) with proximal muscle weakness, early respiratory muscle involvement, and unique muscle biopsy findings to chromosomal region 2q24-31. In this study, a French family with a similar clinical phenotype and pathology (muscle biopsy) was investigated to see whether the disease gene associated with the myopathy is mapped to the same region as the one in the Swedish families; however, chromosomal region 2q24-q31 was completely excluded. In order to localise the disease gene for the French family, a genome-wide scan was performed using polymorphic microsatellite markers. A maximum two-point lod score of 2.11 (the highest lod score that can be achieved in this family) was obtained for the markers in the region between D2S1272 and D2S1260, spanning 4 cM. This result suggests that the gene responsible for the French form is likely to be located on chromosome 2q21.

A radiation hybrid breakpoint map of the acute myeloid leukemia (AML) and limb-girdle muscular dystrophy 1A (LGMD1A) regions of chromosome 5q31 localizing 122 expressed sequences

We have constructed a high-resolution map of a 6-Mb interval of human chromosome 5, band q31, incorporating 175 sequence tagged sites, of which 33 are genetic polymorphisms and 122 are nonredundant expressed sequences. The map was assembled initially as a YAC contig, incorporating data from radiation hybrid maps. To improve resolution and to identify errors in the databases, a radiation hybrid breakpoint map was developed for the interval, which included hybrids from both Stanford G3 and GeneBridge 4 panels. This novel approach facilitated the integration of one RH panel with another and enabled the identification and localization of new, previously unmapped ESTs from the radiation hybrid databases. ESTs were assembled into overlapping transcription units and ordered with respect to polymorphic markers in the region, resulting in a comprehensive map that incorporates markers from multiple different types of maps. This map of 5q31 will facilitate gene discovery efforts for several disorders, including limb-girdle muscular dystrophy type 1A and the genes deleted in acute myeloid leukemias and myelodysplasia. The study demonstrates the utility of a radiation hybrid breakpoint panel for correction of map errors and for the efficient identification of new transcript units in a large genomic interval.

Use of a CEPH meiotic breakpoint panel to refine the locus of limb-girdle muscular dystrophy type 1A (LGMD1A) to a 2-Mb interval on 5q31

Limb-girdle muscular dystrophy type 1A (LGMD1A) is an autosomal dominant disease characterized by progressive weakness of the hip and shoulder girdle. The gene for LGMD1A had been localized to a 7-cM interval at 5q31 in a single large family (Family 39). To refine the localization of LGMD1A further and to aid in its identification, a high-resolution physical map of the locus was used to identify and provisionally localize 25 polymorphic markers. A subset of these markers was then ordered genetically, using a CEPH meiotic breakpoint panel, resulting in an integrated physical-genetic map of the locus. Relevant markers were genotyped on the members of Family 39 who contained informative recombination events, resulting in a further narrowing of LGMD1A to an interval bounded by D5S479 and D5S594, estimated to be 2 Mb in size. Integration of the genetic and physical map permits the identification of several transcription units from within the narrowed LGMD1A interval, including one that is muscle specific, representing candidate genes for this familial dystrophy.

Characterization and mapping of four novel human expressed polymorphic trinucleotide microsatellites

Recently, several important human genetic diseases have been shown to be due to pathological expansion of expressed trinucleotide microsatellites. Discovery of other such 'expansion diseases' will depend on characterization of more expressed loci containing trinucleotide repeats. We searched the expressed sequence tag database (dbEST) for repetitive trinucleotides and selected four loci for further studies (EST00586 EST05486, EST13299 and HHEA48B). For each locus, we have identified size polymorphism by PCR amplification and achieved chromosomal mapping using a somatic hybrid cell panel and the Stanford G3 radiation hybrid panel. Further searches of GenBank, dbEST and UniGene unraveled EST clusters for three of the loci, allowing construction of contigs and, in one instance, identification of a partial open reading frame. Three of the loci were linked to autosomal dominant human genetic diseases whose primary gene defect has not yet been established. Although it is a priori improbable that there is an etiological connection between the loci studied and the diseases, our results demonstrate that dbEST constitutes a useful starting point in the search for candidate loci for new expansion diseases.

Isolation of yeast artificial chromosomes containing the entire transcriptional unit of the human FGF1 gene: a 720-kb contig spanning human chromosome 5q31.3-->q32

The q31-q33 region of chromosome 5 includes a number of genes encoding growth factors, growth factor receptors, and hormone/neurotransmitter receptors. The human fibroblast growth factor 1 locus (FGF1) resides in this region of chromosome 5, which is frequently lost in myelodysplastic syndromes and acute myeloid leukemia patients. Other disease loci, including the loci for limb-girdle muscular dystrophy and an autosomal dominant deafness, have been mapped on this region, but their genes have not been isolated. It was shown that the critical region lost in two patients with the 5q- syndrome resides between FGF1 and IL12B. We previously reported the construction of a yeast artificial chromosome (YAC) contig spanning 330 kb around the FGF1 gene. Here we report the isolation of additional YAC clones that extend 290 kb from the previous contig. Sequence-tagged sites developed from the outermost YAC ends were utilized in the contig cloning of two P1 clones P1Y2 and P1Y8. Together, these YAC and P1 clones span 720 kb around the FGF1 locus. With the use of fluorescence in situ hybridization, a physical map has been constructed of these P1 and GRL (glucocorticoid receptor locus) probes on metaphase and interphase chromosomes. On the basis of our work and the known orientation of GRL transcription, the determined order of these loci on chromosome 5q31.3-q32 is centromere-P1Y8-3'[FGF1]5'-P1Y2-5'[GRL]3'-telome re. Knowing the transcriptional orientation of the FGF1 gene relative to the centromere will now facilitate the directional cloning of clinically important genes that may reside in this region.

Exclusion of identified LGMD1 loci from four dominant limb-girdle muscular dystrophy families

The limb-girdle muscular dystrophies are a clinically and genetically heterogeneous group of disorders. Recent linkage analyses and positional cloning studies have identified numerous loci responsible for the recessive and dominant forms, underscoring the inherent heterogeneity. In this report, we investigate four large autosomal dominant limb-girdle pedigrees and exclude these pedigrees from linkage to these loci. In addition, there is no evidence for linkage to any of the seven recessive LGMD loci.

Using neural networks as an aid in the determination of disease status: comparison of clinical diagnosis to neural-network predictions in a pedigree with autosomal dominant limb-girdle muscular dystrophy

Studies of the genetics of certain inherited diseases require expertise in the determination of disease status even for single-locus traits. For example, in the diagnosis of autosomal dominant limb-girdle muscular dystrophy (LGMD1A), it is not always possible to make a clear-cut determination of disease, because of variability in the diagnostic criteria, age at onset, and differential presentation of disease. Mapping such diseases is greatly simplified if the data present a homogeneous genetic trait and if disease status can be reliably determined. Here, we present an approach to determination of disease status, using methods of artificial neural-network analysis. The method entails "training" an artificial neural network, with input facts (based on diagnostic criteria) and related results (based on disease diagnosis). The network contains weight factors connecting input "neurons" to output "neurons," and these connections are adjusted until the network can reliably produce the appropriate outputs for the given input facts. The trained network can be "tested" with a second set of facts, in which the outcomes are known but not provided to the network, to see how well the training has worked. The method was applied to members of a pedigree with LGMD1A, now mapped to chromosome 5q. We used diagnostic criteria and disease status to train a neural network to classify individuals as "affected" or "not affected." The trained network reproduced the disease diagnosis of all individuals of known phenotype, with 98% reliability. This approach defined an appropriate choice of clinical factors for determination of disease status. Additionally, it provided insight into disease classification of those considered to have an "unknown" phenotype on the basis of standard clinical diagnostic methods.

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.

Limb girdle muscular dystrophy in Manitoba Hutterites does not map to any of the known LGMD loci

Limb girdle muscular dystrophy (LGMD) is a heterogeneous group of disorders affecting primarily the shoulder and pelvic girdles. Autosomal dominant and recessive forms have been identified; 8 have been mapped and 1 more has been postulated on the basis of exclusion of linkage. An autosomal recessive muscular dystrophy was first described in 1976 in the Hutterite Brethren, a North American genetic and religious isolate [Shokeir and Kobrinsky, 1976; Clin Genet 9:197-202]. In this report, we discuss the results of linkage analysis in 4 related Manitoba Hutterite sibships with 21 patients affected with a mild autosomal recessive form of LGMD. Because of the difficulties in assigning a phenotype in some asymptomatic individuals, stringent criteria for the affected phenotype were employed. As a result, 7 asymptomatic relatives with only mildly elevated CK levels were assigned an unknown phenotype to prevent their possible misclassification. Two-point linkage analysis of the disease locus against markers linked to 7 of the known LGMD loci and 3 other candidate genes yielded lod scores of < or = -2 at theta = 0.01 in all cases and in most cases at theta = 0.05. This suggests that there is at least 1 additional locus for LGMD.

Limb girdle muscular dystrophy: a prospective follow-up study of functional impairment

This 6-year prospective follow-up study evaluated the rate of clinical disease progression in 19 of 20 previously reported patients with strictly selected limb girdle muscular dystrophy. There was no significant deterioration in muscle strength (assessed by manual muscle testing). An activities of daily living (ADL) scale showed significant functional deterioration in 30% of patients with predominant involvement in a single functional domain variable between patients, and determined by the patient's previous level of function. A functional grading system showed that 70% of patients had deteriorated at least one grade in the arms and/or legs. Deterioration of the ADL score correlated with the loss of functional grades. We conclude that assessment of functional ability may be more sensitive to detect clinical disease progression compared to testing of muscle strength. The clinical parameter that correlates best with the activity of the underlying disease process is not determined. Tests for strength and functional impairment are complementary. Patients expressed appreciation that functional disability was addressed during follow-up visits.

Characterization of delta-sarcoglycan, a novel component of the oligomeric sarcoglycan complex involved in limb-girdle muscular dystrophy

The sarcoglycan complex is known to be involved in limb-girdle muscular dystrophy (LGMD) and is composed of at least three proteins: alpha-, beta-, and gamma-sarcoglycan. delta-Sarcoglycan has now been identified as a second 35-kDa sarcolemmal transmembrane glycoprotein that shares high homology with gamma-sarcoglycan and is expressed mainly in skeletal and cardiac muscle. Biochemical analysis has demonstrated that gamma- and delta-sarcoglycan are separate entities within the sarcoglycan complex and that all four sarcoglycans exist in the complex on a stoichiometrically equal basis. Immunohistochemical analysis of skeletal muscle biopsies from patients with LGMD2C, LGMD2D, and LGMD2E demonstrated a reduction of the entire sarcoglycan complex in these muscular dystrophies. Furthermore, we have mapped the human delta-sarcoglycan gene to chromosome 5q33-q34 in a region overlapping the recently linked autosomal recessive LGMD2F locus.

Investigation of muscle disease

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