A gene for autosomal recessive limb-girdle muscular dystrophy in Manitoba Hutterites maps to chromosome region 9q31-q33: evidence for another limb-girdle muscular dystrophy locus

Case report: A novel patient presenting TRIM32-related limb-girdle muscular dystrophy

Limb-girdle muscular dystrophy autosomal recessive 8 (LGMDR8) is a rare clinical manifestation caused by the presence of biallelic variants in the TRIM32 gene. We present the clinical, molecular, histopathological, and muscle magnetic resonance findings of a novel 63-years-old LGMDR8 patient of Italian origins, who went undiagnosed for 24 years. Clinical exome sequencing identified two TRIM32 missense variants, c.1181G > A p.(Arg394His) and c.1781G > A p.(Ser594Asp), located in the NHL1 and NHL4 structural domains, respectively, of the TRIM32 protein. We conducted a literature review of the clinical and instrumental data associated to the so far known 26 TRIM32 variants, carried biallelically by 53 LGMDR8 patients reported to date in 20 papers. Our proband's variants were previously identified only in three independent LGMDR8 patients in homozygosis, therefore our case is the first in literature to be described as compound heterozygous for such variants. Our report also provides additional data in support of their pathogenicity, since p.(Arg394His) is currently classified as a variant of uncertain significance, while p.(Ser594Asp) as likely pathogenic. Taken together, these findings might be useful to improve both the genetic counseling and the diagnostic accuracy of this rare neuromuscular condition.

Tripartite Motif-Containing Protein 32 (TRIM32): What Does It Do for Skeletal Muscle?

Tripartite motif-containing protein 32 (TRIM32) is a member of the tripartite motif family and is highly conserved from flies to humans. Via its E3 ubiquitin ligase activity, TRIM32 mediates and regulates many physiological and pathophysiological processes, such as growth, differentiation, muscle regeneration, immunity, and carcinogenesis. TRIM32 plays multifunctional roles in the maintenance of skeletal muscle. Genetic variations in the TRIM32 gene are associated with skeletal muscular dystrophies in humans, including limb-girdle muscular dystrophy type 2H (LGMD2H). LGMD2H-causing genetic variations of TRIM32 occur most frequently in the C-terminal NHL (ncl-1, HT2A, and lin-41) repeats of TRIM32. LGMD2H is characterized by skeletal muscle dystrophy, myopathy, and atrophy. Surprisingly, most patients with LGMD2H show minimal or no dysfunction in other tissues or organs, despite the broad expression of TRIM32 in various tissues. This suggests more prominent roles for TRIM32 in skeletal muscle than in other tissues or organs. This review is focused on understanding the physiological roles of TRIM32 in skeletal muscle, the pathophysiological mechanisms mediated by TRIM32 genetic variants in LGMD2H patients, and the correlations between TRIM32 and Duchenne muscular dystrophy (DMD).

Tripartite motif-containing protein 32 regulates Ca2+ movement in skeletal muscle

Mutations in tripartite motif-containing protein 32 (TRIM32), especially in NHL repeats, have been found in skeletal muscle in patients with type 2H limb-girdle muscular dystrophy (LGMD2H). However, the roles of the NHL repeats of TRIM32 in skeletal muscle functions have not been well addressed. In the present study, to examine the functional role(s) of the TRIM32 NHL repeats in skeletal muscle, TRIM32-binding proteins in skeletal muscle were first searched using a binding assay and MALDI-TOF/TOF. Sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase 1a (SERCA1a) was found to be a TRIM32-binding protein. Next, a deletion mutant of TRIM32 missing the NHL repeats (NHL-Del) was expressed in mouse primary skeletal myotubes during myoblast differentiation into myotubes. Ca²⁺ movement in the myotubes was examined using single-cell Ca²⁺ imaging. Unlike wild-type (WT) TRIM32, NHL-Del did not enhance the amount of Ca²⁺ release from the sarcoplasmic reticulum (SR), Ca²⁺ release for excitation-contraction (EC) coupling, or extracellular Ca²⁺ entry via store-operated Ca²⁺ entry (SOCE). In addition, even compared with the vector control, NHL-Del resulted in reduced SOCE due to reduced expression of extracellular Ca²⁺ entry channels. Transmission electron microscopy (TEM) observation of the myotubes revealed that NHL-Del induced the formation of abnormal vacuoles and tubular structures in the cytosol. Therefore, by binding to SERCA1a via its NHL repeats, TRIM32 may participate in the regulation of Ca²⁺ movement for skeletal muscle contraction and the formation of cellular vacuoles and tubular structures in skeletal muscle. Functional defects in TRIM32 due to mutations in NHL repeats may be pathogenic toward LGMD2H.

Sarcotubular Myopathy Due to Novel TRIM32 Mutation in Association with Multiple Sclerosis

Azerbaijani 28-year-old female showed weakness (MRC (Medical Research Council Scale for Muscle Strength) grade 4 in the proximal part of the upper and MRC grade 2–3 in the lower extremities), difficulty in stair lifting, positive symptom of Hoover’s rising, «waddling gait», decline deep reflexes symmetrical, lack of surface reflexes, positive Babinsky’s reflex on the right, urinary incontinence during sneezing, prolonged walking and exercise from puberty. Additional methods made it possible to identify minor violations of conduction of the left ventricle, electromyography signs of primary muscular disease with predominant involvement of the proximal muscles of the lower extremities, elevation of serum creatine kinase (746.81 U/l), active foci of demyelination in the left frontal lobe, intrathecal synthesis of oligoclonal IgG bands (type 2) in cerebrospinal fluid, atrophy and fatty degeneration of all muscles of the shins, homozygous Variant of Uncertain Significance (VUS) c.1855C > T (p.Pro619Ser) in TRIM32 gene and heterozygous VUS c.2300C > G (p.Thr767Arg) in KIF5A, c.2840G > A (p.Arg947Lys) in MYH2, c.1502G > C (p.Gly501Ala) in POMT1 genes. Comparison of the phenotypes of the mutations that have been identified with the clinical picture of the patient suggests that VUS c.1855C > T (p.Pro619Ser) in the TRIM32 gene can be pathological. Summarizing, it can be argued that the cause of the identified disorders is a homozygous variant c.1855C > T (p.Pro619Ser) in TRIM32 gene that causes LGMDR8 in a patient with MS.

Analysis of the Zn-Binding Domains of TRIM32, the E3 Ubiquitin Ligase Mutated in Limb Girdle Muscular Dystrophy 2H

Members of the tripartite motif family of E3 ubiquitin ligases are characterized by the presence of a conserved N-terminal module composed of a RING domain followed by one or two B-box domains, a coiled-coil and a variable C-terminal region. The RING and B-box are both Zn-binding domains but, while the RING is found in a large number of proteins, the B-box is exclusive to the tripartite motif (TRIM) family members in metazoans. Whereas the RING has been extensively characterized and shown to possess intrinsic E3 ligase catalytic activity, much less is known about the role of the B-box domains. In this study, we adopted an in vitro approach using recombinant point- and deletion-mutants to characterize the contribution of the TRIM32 Zn-binding domains to the activity of this E3 ligase that is altered in a genetic form of muscular dystrophy. We found that the RING domain is crucial for E3 ligase activity and E2 specificity, whereas a complete B-box domain is involved in chain assembly rate modulation. Further, in vitro, the RING domain is necessary to modulate TRIM32 oligomerization, whereas, in cells, both the RING and B-box cooperate to specify TRIM32 subcellular localization, which if altered may impact the pathogenesis of diseases.

TRIM32 ubiquitin E3 ligase, one enzyme for several pathologies: From muscular dystrophy to tumours

TRIM32 is a member of the TRIpartite Motif family characterised by the presence of an N-terminal three-domain-module that includes a RING domain, which confers E3 ubiquitin ligase activity, one or two B-box domains and a Coiled-Coil region that mediates oligomerisation. Several TRIM32 substrates were identified including muscular proteins and proteins involved in cell cycle regulation and cell motility. As ubiquitination is a versatile post-translational modification that can affect target turnover, sub-cellular localisation or activity, it is likely that diverse substrates may be differentially affected by TRIM32-mediated ubiquitination, reflecting its multi-faceted roles in muscle physiology, cancer and immunity. With particular relevance for muscle physiology, mutations in TRIM32 are associated with autosomal recessive Limb-Girdle Muscular Dystrophy 2H, a muscle-wasting disease with variable clinical spectrum ranging from almost asymptomatic to wheelchair-bound patients. In this review, we will focus on the ability of TRIM32 to mark specific substrates for proteasomal degradation discussing how the TRIM32-proteasome axis may (i) be important for muscle homeostasis and for the pathogenesis of muscular dystrophy; and (ii) define either an oncogenic or tumour suppressive role for TRIM32 in the context of different types of cancer.

Limb-girdle muscular dystrophies - international collaborations for translational research

The limb-girdle muscular dystrophies (LGMDs) are a diverse group of genetic neuromuscular conditions that usually manifest in the proximal muscles of the hip and shoulder girdles. Since the identification of the first gene associated with the phenotype in 1994, an extensive body of research has identified the genetic defects responsible for over 30 LGMD subtypes, revealed an increasingly varied phenotypic spectrum, and exposed the need to move towards a systems-based understanding of the molecular pathways affected. New sequencing technologies, including whole-exome and whole-genome sequencing, are continuing to expand the range of genes and phenotypes associated with the LGMDs, and new computational approaches are helping clinicians to adapt to this new genomic medicine paradigm. However, 60 years on from the first description of LGMD, no curative therapies exist, and systematic exploration of the natural history is still lacking. To enable rapid translation of basic research to the clinic, well-phenotyped and genetically characterized patient cohorts are a necessity, and appropriate outcome measures and biomarkers must be developed through natural history studies. Here, we review the international collaborations that are addressing these translational research issues, and the lessons learned from large-scale LGMD sequencing programmes.

Tripartite motif 32 prevents pathological cardiac hypertrophy

This study presents the first evidence that TRIM32 protects against pathological cardiac hypertrophy by suppressing Akt-dependent signalling pathways. Therefore TRIM32 might be a potential therapeutic strategy for the prevention and treatment of cardiac hypertrophy and heart failure.

TRIM32 (tripartite motif 32) is widely accepted to be an E3 ligase that interacts with and eventually ubiquitylates multiple substrates. TRIM32 mutants have been associated with LGMD-2H (limb girdle muscular dystrophy 2H). However, whether TRIM32 is involved in cardiac hypertrophy induced by biomechanical stresses and neurohumoral mediators remains unclear. We generated mice and isolated NRCMs (neonatal rat cardiomyocytes) that overexpressed or were deficient in TRIM32 to investigate the effect of TRIM32 on AB (aortic banding) or AngII (angiotensin II)-mediated cardiac hypertrophy. Echocardiography and both pathological and molecular analyses were used to determine the extent of cardiac hypertrophy and subsequent fibrosis. Our results showed that overexpression of TRIM32 in the heart significantly alleviated the hypertrophic response induced by pressure overload, whereas TRIM32 deficiency dramatically aggravated pathological cardiac remodelling. Similar results were also found in cultured NRCMs incubated with AngII. Mechanistically, the present study suggests that TRIM32 exerts cardioprotective action by interruption of Akt- but not MAPK (mitogen-dependent protein kinase)-dependent signalling pathways. Additionally, inactivation of Akt by LY294002 offset the exacerbated hypertrophic response induced by AB in TRIM32-deficient mice. In conclusion, the present study indicates that TRIM32 plays a protective role in AB-induced pathological cardiac remodelling by blocking Akt-dependent signalling. Therefore TRIM32 could be a novel therapeutic target for the prevention of cardiac hypertrophy and heart failure.

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.

Limb-girdle muscular dystrophy 2H and the role of TRIM32

Limb-girdle muscular dystrophy (LGMD) 2H is a slowly progressive condition characterized by proximal weakness, atrophy, and mildly to moderately raised levels of creatine kinase. Facial weakness, scapular winging, hypertrophied calves, and Achilles tendon contractions are not uncommon and the age of onset ranges between the first and fourth decade. LGMD2H was originally described in the Hutterite population that resides in central Canada and the Dakotas of the USA. LGMD2H was mapped to a specific mutation in the TRIM32 gene and it has subsequently been shown that the same mutation also results in the "sarcotubular myopathy" syndrome, which was described histopathologically. TRIM32 appears to be an E3 ubiquitin ligase, containing the tripartite motif common to this family of proteins (RING finger, B-box, coiled-coil). A few substrates have been identified, including actin and dysbindin. Recent studies have identified additional mutations in the C-terminal region of TRIM32 that result in a dystrophic myopathy. Although TRIM32 appears to be expressed ubiquitously, it is still not clear why certain mutations of TRIM32 would result in a phenotype relatively restricted to skeletal muscle. A mutation in the B-box region of TRIM32 has also been shown to result in a more pleiotropic disorder, Bardet-Biedl Syndrome (BBS11). This disorder is associated with obesity, retinopathy, diabetes, polydactyly, renal abnormalities, learning disability, and hypogenitalism. It is likely that C-terminal mutations in TRIM32 affect the ability of muscle proteins to be degraded by the ubiquitin-proteasome pathway.

Muscular dystrophies: an update on pathology and diagnosis

Muscular dystrophies are clinically, genetically, and molecularly a heterogeneous group of neuromuscular disorders. Considerable advances have been made in recent years in the identification of causative genes, the differentiation of the different forms and in broadening the understanding of pathogenesis. Muscle pathology has an important role in these aspects, but correlation of the pathology with clinical phenotype is essential. Immunohistochemistry has a major role in differential diagnosis, particularly in recessive forms where an absence or reduction in protein expression can be detected. Several muscular dystrophies are caused by defects in genes encoding sarcolemmal proteins, several of which are known to interact. Others are caused by defects in nuclear membrane proteins or enzymes. Assessment of both primary and secondary abnormalities in protein expression is useful, in particular the hypoglycosylation of alpha-dystroglycan. In dominantly inherited muscular dystrophies it is rarely possible to detect a change in the expression of the primary defective protein; an exception to this is caveolin-3.

Shades of gray: a comparison of linkage disequilibrium between Hutterites and Europeans

Founder or isolated populations have advantages for genetic studies due to decreased genetic and environmental heterogeneity. However, whereas longer-range linkage disequilibrium (LD) in these populations is expected to facilitate gene localization, extensive LD may actually limit the ability for gene discovery. The North American Hutterite population is one of the best characterized young founder populations and members of this isolate have been the subjects of our studies of complex traits, including fertility, asthma and cardiovascular disease, for >20 years. Here, we directly assess the patterns and extent of global LD using single nucleotide polymorphism genotypes with minor allele frequencies (MAFs) > or =5% from the Affymetrix GeneChip Mapping 500 K array in 60 relatively unrelated Hutterites and 60 unrelated Europeans (HapMap CEU). Although LD among some marker pairs extends further in the Hutterites than in Europeans, the pattern of LD and MAF are surprisingly similar. These results indicate that (1) identifying disease genes should be no more difficult in the Hutterites than in outbred European populations, (2) the same common susceptibility alleles for complex diseases should be present in the Hutterites and outbred European populations, and (3) imputation algorithms based on HapMap CEU should be applicable to the Hutterites.

Use of SNP array analysis to identify a novel TRIM32 mutation in limb-girdle muscular dystrophy type 2H

Molecular diagnosis of monogenic diseases with high genetic heterogeneity is usually challenging. In the case of limb-girdle muscular dystrophy, multiplex Western blot analysis is a very useful initial step, but that often fails to identify the primarily affected protein. We report how homozygosity analysis using a genome-wide SNP array allowed us to solve the diagnostic enigma in a patient with a moderate form of LGMD, born from consanguineous parents. The genome-wide scan performed on the patient's DNA revealed several regions of homozygosity, that were compared to the location of known LGMD genes. One such region indeed contained the TRIM32 gene. This gene was previously found mutated in families with limb-girdle muscular dystrophy type 2H (LGMD2H), a mild autosomal recessive myopathy described in Hutterite populations and in 4 patients with a diagnosis of sarcotubular myopathy. A single missense mutation was found in all these patients, located in a conserved domain of the C-terminal part of the protein. Another missense mutation affecting the N-terminal part of TRIM32, observed in a single consanguineous Bedouin family, was reported to cause the phenotypically unrelated and genetically heterogeneous Bardet-Biedl syndrome, defining the BBS11 locus. Sequencing of TRIM32 in our patient revealed a distal frameshift mutation, c.1753_1766dup14 (p.Ile590Leu fsX38). Together with two recently reported mutations, this novel mutation confirms that integrity of the C-terminal domain of TRIM32 is necessary for muscle maintenance.

A first stage genome-wide screen for regions shared identical-by-descent in Hutterite families with multiple sclerosis

The complexity of multiple sclerosis (MS) genetics has made the search for novel genes using traditional sharing methods problematic. In order to minimize the genetic heterogeneity present in the MS population we have screened the Canadian MS population for individuals belonging to the Hutterite Brethren. Seven Hutterites with clinically definite MS were ascertained and are related to a common founder by eight generations. Six of the 7 affected individuals and 21 of their unaffected family members (total = 27) were genotyped for 807 markers. Haplotypes were then inspected for sharing among the six MS patients. There were three haplotypes shared among all six MS patients. The haplotypes were located at 2q34-35, 4q31-32, and 17p13. An additional 15 haplotypes were shared among five of the six Hutterites MS patients. The HLA Class II region was one of the highlighted regions; however, the shared MHC haplotype bore the DRB1*04 allele and not the MS-associated DRB1*15 allele providing further evidence of the complexity of the MHC. Additional genotyping to refine the haplotypes followed by screening for potential variants may lead to the identification of a novel MS susceptibility gene(s) in this unique population.

Limb-girdle muscular dystrophy: diagnostic evaluation, frequency and clues to pathogenesis

We characterized the frequency of limb-girdle muscular dystrophy (LGMD) subtypes in a cohort of 76 Australian muscular dystrophy patients using protein and DNA sequence analysis. Calpainopathies (8%) and dysferlinopathies (5%) are the most common causes of LGMD in Australia. In contrast to European populations, cases of LGMD2I (due to mutations in FKRP) are rare in Australasia (3%). We have identified a cohort of patients in whom all common disease candidates have been excluded, providing a valuable resource for identification of new disease genes. Cytoplasmic localization of dysferlin correlates with fiber regeneration in a subset of muscular dystrophy patients. In addition, we have identified a group of patients with unidentified forms of LGMD and with markedly abnormal dysferlin localization that does not correlate with fiber regeneration. This pattern is mimicked in primary caveolinopathy, suggesting a subset of these patients may also possess mutations within proteins required for membrane targeting of dysferlin.

Molecular basis of succinylcholine sensitivity in a prairie Hutterite kindred and genetic characterization of the region containing the BCHE gene

The tetrameric glycoprotein butyrylcholinesterase (BChE; EC 3.1.1.8) is one of two enzymes that hydrolyze choline esters. The controlling gene (BCHE) is comprised of four coding exons and is located on chromosome 3q26. Based on BChE activity measurements in the presence and absence of dibucaine, usual (designated U) and atypical (designated A) gene products have been distinguished. Homozygotes for the A gene product are at risk for prolonged apnea following exposure to the surgical anesthetics succinylcholine or mivacurium. In this report, we detail biochemical and molecular investigations of succinylcholine sensitivity in a prairie Hutterite kindred. Our results establish that BChE activities in the family members are impacted by two distinct BCHE mutations, namely, c.209A>G p. D70G and c.1615G>A p. A539T. However, homozygotes for the c.209A>G mutation (i.e., atypical or A) are the only individuals whose BChE activity could lead to adverse reactions to succinylcholine. Interestingly, haplotype analysis of the chromosomal region containing BCHE indicates that the c.209A>G mutation is carried on a unique haplotype, suggesting that it was likely introduced into the population only once. Conversely, the c.1615G>A mutation is carried on various haplotypes and was likely introduced into the population more than once.

The most common mutation in FKRP causing limb girdle muscular dystrophy type 2I (LGMD2I) may have occurred only once and is present in Hutterites and other populations

Limb girdle muscular dystrophy (LGMD) is common in the Hutterite population of North America. We previously identified a mutation in the TRIM32 gene in chromosome region 9q32, causing LGMD2H in approximately two-thirds of the 60 Hutterite LGMD patients studied to date. A genomewide scan was undertaken in five families who did not show linkage to the LGMD2H locus on chromosome 9. A second LGMD locus, LGMD2I, was identified in chromosome region 19q13.3, and the causative mutation was identified as c.826C>A (L276I), a missense mutation in the FKRP gene. A comparison of the clinical characteristics of the two LGMD patient groups in this population reveals some differences. LGMD2I patients generally have an earlier age at diagnosis, a more severe course, and higher serum creatine kinase (CK) levels. In addition, some of these patients show calf hypertrophy, cardiac symptoms, and severe reactions to general anesthesia. None of these features are present among LGMD2H patients. A single common haplotype surrounding the FKRP gene was identified in the Hutterite LGMD2I patients. An identical core haplotype was also identified in 19 other non-Hutterite LGMD2I patients from Europe, Canada, and Brazil. The occurrence of this mutation on a common core haplotype suggests that L276I is a founder mutation that is dispersed among populations of European origin.

Limb-girdle muscular dystrophy: an immunohistochemical diagnostic approach

The limb-girdle muscle dystrophy (LGMD) represents a heterogeneous group of muscular diseases with dominant and recessive inheritance, individualized by gene mutation. A group of 56 patients, 32 males and 24 females, with suggestive LGMD diagnosis were submitted to clinical evaluation, serum muscle enzymes, electromyography, muscle biopsy, and the immunoidentification (ID) of sarcoglycans (SG) alpha, beta, gamma and delta, dysferlin and western blot for calpain-3. All the patients had normal ID for dystrophin (rod domain, carboxyl and amine terminal). The alpha-SG was normal in 42 patients, beta-SG in 28, beta-SG in 45, deltaSG in 32, dysferlin in 37 and calpain-3 in 9. There was a reduction in the alpha-SG in 7 patients, beta-SG in 4, gamma-SG in 2, and delta-SG in 8. There was deficiency of alpha-SG in 7 patients, beta-SG in 6, gamma-SG in 9, delta-SG in 5, dysferlin in 8, and calpain-3 in 5. The patients were grouped according the ID as sarcoglycans deficiency 18 cases, dysferlin deficiency 8 cases and calpain-3 deficiency 5 cases. Only the sarcoglycans deficiency group showed calf hypertrophy. The dysferlin deficiency group was more frequent in females and the onset was later than sarcoglycan and calpain-3 deficiency groups. The calpain-3 deficiency group occurred only in males and showed an earlier onset and weaker muscular strength.

Hutterite brothers both affected with two forms of limb girdle muscular dystrophy: LGMD2H and LGMD2I

Limb girdle muscular dystrophy (LGMD) is very common in the Hutterite population of the North American Prairies. We have recently reported the homozygous c.1459G>A mutation in TRIM32 associated with LGMD2H. We have also identified Hutterite patients with LGMD2I, homozygous for the common c.826C>A mutation in FKRP. To date, all Hutterites with LGMD have been shown to be homozygous for either the TRIM32 or FKRP mutation. We now report a Hutterite family in which both parents and five sons were all found to be homozygous for the TRIM32 mutation. The father had slowly progressive proximal muscle weakness, whereas three sons and their mother, all currently asymptomatic, had normal physical examinations. The remaining two sons (7 and 10 years old), presented with mild decrease in stamina, had normal neuromuscular examinations and were found to be homozygous for the FKRP mutation in addition to the TRIM32 mutation. These two boys do not differ in age at or mode of presentation, physical findings, or serum CK levels compared to age-matched individuals affected with LGMD2I alone. This suggests that the effects of these two mutations are not acting synergistically at this time. It remains to be seen whether there will be signs of interaction between these two mutations as the patients get older.

A locus for Bowen-Conradi syndrome maps to chromosome region 12p13.3

Bowen-Conradi syndrome (BCS) is a lethal autosomal recessive disorder with an estimated incidence of 1 in 355 live births in the Hutterite population. A few cases have been reported in other populations. Here, we report the results of a genome-wide scan and fine mapping of the BCS locus in Hutterite families. By linkage and haplotype analysis the BCS locus was mapped to a 3.5 cM segment (1.9 Mbp) in chromosome region 12p13.3 bounded by F8VWF and D12S397. When genealogical relationships among the families were taken into account in the linkage analysis, the evidence for linkage was stronger and the number of potentially linked regions was reduced to one. Under the assumption that all the Hutterite patients were identical by descent for a disease-causing mutation, haplotype analysis was used to infer likely historical recombinants and thereby narrow the candidate region to a chromosomal segment shared in common by all the affected children. This study also demonstrates that BCS and cerebro-oculo-facial-skeletal syndrome (COFS) are genetically distinct.

Commonality ofTRIM32mutation in causing sarcotubular myopathy and LGMD2H

Sarcotubular myopathy (OMIM 268950) is a rare autosomal recessive myopathy first described in two Hutterite brothers from South Dakota and in two non-Hutterite brothers from Germany. We report that sarcotubular myopathy (STM) is caused by mutation in TRIM32, the gene encoding the tripartite motif-containing protein 32. TRIM32 was found to be the gene mutated in limb girdle muscular dystrophy type 2H (LGMD2H [OMIM 254110]), a disorder that has been confined to the Hutterite population. The TRIM32 mutation found in the STM patients is identical to the causative mutation for LGMD2H (D487N), Haplotype analysis shows that the disease chromosomes share common ancestry.

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.

Genetic studies of neuropsychiatric disorders in Costa Rica: a model for the use of isolated populations

The importance of genetics in understanding the etiology of mental illness has become increasingly clear in recent years, as more evidence has mounted that almost all neuropsychiatric disorders have a genetic component. It has also become clear, however, that these disorders are etiologically complex, and multiple genetic and environmental factors contribute to their makeup. So far, traditional linkage mapping studies have not definitively identified specific disease genes for neuropsychiatric disorders, although some potential candidates have been identified via these methods (e.g. the dysbindin gene in schizophrenia; Straub et al., 2002; Schwab et al., 2003). For this reason, alternative approaches are being attempted, including studies in genetically isolated populations. Because isolated populations have a high degree of genetic homogeneity, their use may simplify the process of identifying disease genes in disorders where multiple genes may play a role. Several areas of Latin America contain genetically isolated populations that are well suited for the study of neuropsychiatric disorders. Genetic studies of several major psychiatric illnesses, including bipolar disorder, major depression, schizophrenia, Tourette Syndrome, alcohol dependence, attention deficit hyperactivity disorder, and obsessive-compulsive disorder, are currently underway in these regions. In this paper we highlight the studies currently being conducted by our groups in the Central Valley of Costa Rica to illustrate the potential advantages of this population for genetic studies.

Limb-girdle muscular dystrophies - from genetics to molecular pathology

The limb-girdle muscular dystrophies are a diverse group of muscle-wasting disorders characteristically affecting the large muscles of the pelvic and shoulder girdles. Molecular genetic analyses have demonstrated causative mutations in the genes encoding a disparate collection of proteins involved in all aspects of muscle cell biology. Muscular dystrophy includes a spectrum of disorders caused by loss of the linkage between the extracellular matrix and the actin cytoskeleton. Within this are the forms of limb-girdle muscular dystrophy caused by deficiencies of the sarcoglycan complex and by aberrant glycosylation of alpha-dystroglycan caused by mutations in the fukutin-related protein gene. However, other forms of this disease have distinct pathophysiological mechanisms. For example, deficiency of dysferlin disrupts sarcolemmal membrane repair, whilst loss of calpain-3 may exert its pathological influence either by perturbation of the IkappaBalpha/NF-kappaB pathway, or through calpain-dependent cytoskeletal remodelling. Caveolin-3 is implicated in numerous cell-signalling pathways and involved in the biogenesis of the T-tubule system. Alterations in the nuclear lamina caused by mutations in laminA/C, sarcomeric changes in titin, telethonin or myotilin at the Z-disc, and subtle changes in the extracellular matrix proteins laminin-alpha2 or collagen VI can all lead to a limb-girdle muscular dystrophy phenotype, although the specific pathological mechanisms remain obscure. Differential diagnosis of these disorders requires the careful application of a broad range of disciplines: clinical assessment, immunohistochemistry and immunoblotting using a panel of antibodies and extensive molecular genetic analyses.

Limb-girdle muscular dystrophy 2I: phenotypic variability within a large consanguineous Bedouin family associated with a novel FKRP mutation

Limb-girdle muscular dystrophies (LGMDs) represent a group of diseases characterized mainly by muscle wasting of the upper and lower limbs, with a wide range of clinical severity. The clinical heterogeneity is paralleled by molecular heterogeneity; each of the 10 forms of autosomal-recessive LGMD recognized to date is caused by mutations in a distinct gene. In a large consanguineous Bedouin tribe living in northern Israel, 15 individuals affected by LGMD demonstrate an autosomal recessive pattern of inheritance. A genome-wide screen followed by fine mapping in this family revealed linkage to a region on chromosome 19 harboring the fukutin-related protein gene (FKRP), with a maximal LOD score of 4.8 for D19S902. FKRP, encoding a putative glycosyltransferase, has been implicated in causing congenital muscular dystrophy 1C (MDC1C), and has recently been shown to be mutated in LGMD2I. We identified a novel missense mutation in exon 4 of the FKRP gene in all the patients studied. Although all affected individuals were homozygous for the same mutation, a marked phenotypic variability was apparent within the family. This finding may suggest a role of modifier genes and environmental factors in LGMD2I. Moreover, the demonstration that an identical, novel mutation in the FKRP gene can cause a muscle disease of either a congenital onset or of a later onset within a single family provides clinical support to the molecular evidence, suggesting that MDC1C and LGMD2I are overlapping ends of one and the same entity.

The limb girdle muscular dystrophies: our ever-expanding knowledge

The limb girdle muscular dystrophies (LGMDs) represent a genetically diverse group of disorders. Currently, chromosomal loci are known for at least 5 autosomal-dominant and 10 autosomal-recessive subgroups. In 13 of these, recognized genes and protein products generate an assortment of phenotypes, some unique and many overlapping. In some disorders, novel clinical features are sufficiently distinct so as to proffer clues to the diagnosis of a specific LGMD subtype. An armamentarium of laboratory tools is required to confirm specific subtypes of LGMD. These might only be available in neuromuscular centers specializing in this form of dystrophy. Currently, supportive therapy is the predominant means of treatment, but further understanding of unique pathogenic mechanisms holds promise for the future.

The 10 autosomal recessive limb-girdle muscular dystrophies

Fifteen forms of limb-girdle muscular dystrophies (5 autosomal dominant and 10 autosomal recessive) have already been found. The 10 genes responsible for the autosomal recessive forms, which account for more than 90% of the cases, had their product identified. This review will focus on the most recent data on autosomal recessive-limb-girdle muscular dystrophy and on our own experience of more than 300 patients studied from 120 families who were classified (based on DNA, linkage and muscle protein analysis) in eight different forms of autosomal recessive-limb-girdle muscular dystrophy. Genotype-phenotype correlations in this highly heterogeneous group confirm that patients with mutations in different genes may be clinically indistinguishable. On the other hand, for most forms of autosomal recessive-limb-girdle muscular dystrophy a discordant phenotype, ranging from a relatively severe course to mildly affected or asymptomatic carriers may be seen in patients carrying the same mutation even within the same family. A gender difference in the severity of the phenotype might exist for some forms of autosomal recessive-limb-girdle muscular dystrophy, such as calpainopathy and telethoninopathy but not for others, such as dysferlinopathies or sarcoglycanopathies. Understanding similarities in patients affected by mutations in different genes, differences in patients carrying the same mutations or why some muscles are affected while others are spared remains a major challenge. It will depend on future knowledge of gene expression, gene and protein interactions and on identifying modifying genes and other factors underlying clinical variability.

Protein defects in neuromuscular diseases

Muscular dystrophies are a heterogeneous group of genetically determined progressive disorders of the muscle with a primary or predominant involvement of the pelvic or shoulder girdle musculature. The clinical course is highly variable, ranging from severe congenital forms with rapid progression to milder forms with later onset and a slower course. In recent years, several proteins from the sarcolemmal muscle membrane (dystrophin, sarcoglycans, dysferlin, caveolin-3), from the extracellular matrix (alpha2-laminin, collagen VI), from the sarcomere (telethonin, myotilin, titin, nebulin), from the muscle cytosol (calpain 3, TRIM32), from the nucleus (emerin, lamin A/C, survival motor neuron protein), and from the glycosylation pathway (fukutin, fukutin-related protein) have been identified. Mutations in their respective genes are responsible for different forms of neuromuscular diseases. Protein analysis using Western blotting or immunohistochemistry with specific antibodies is of the utmost importance for the differential diagnosis and elucidation of the physiopathology of each genetic disorder involved. Recent molecular studies have shown clinical inter- and intra-familial variability in several genetic disorders highlighting the importance of other factors in determining phenotypic expression and the role of possible modifying genes and protein interactions. Developmental studies can help elucidate the mechanism of normal muscle formation and thus muscle regeneration. In the last fifteen years, our research has focused on muscle protein expression, localization and possible interactions in patients affected by different forms of muscular dystrophies. The main objective of this review is to summarize the most recent findings in the field and our own contribution.

Limb-girdle muscular dystrophy

The limb-girdle muscular dystrophies (LGMDs) are a group of muscular dystrophies that share a similar clinical phenotype. Despite this clinical homogeneity, at least 15 different genetic forms of LGMD are now known. Some of these share pathogenetic mechanisms with other forms of muscular dystrophy, such as the sarcoglycanopathies (LGMD 2C-F) and the dystrophinopathies (Duchenne and Becker muscular dystrophy). Some are allelic with other forms of muscular dystrophy; LGMD 1B is allelic with autosomal dominant Emery-Dreifuss muscular dystrophy. Still others introduce totally unique pathogenetic mechanisms to the study of muscular dystrophy. For example, LGMD 2H appears to be due to mutations affecting the ubiquitin-proteasome pathway. A diagnostic approach is outlined based on clinical features, genetics, and commercially available testing.

Telethonin protein expression in neuromuscular disorders

Telethonin is a 19-kDa sarcomeric protein, localized to the Z-disc of skeletal and cardiac muscles. Mutations in the telethonin gene cause limb-girdle muscular dystrophy type 2G (LGMD2G). We investigated the sarcomeric integrity of muscle fibers in LGMD2G patients, through double immunofluorescence analysis for telethonin with three sarcomeric proteins: titin, alpha-actinin-2, and myotilin and observed the typical cross striation pattern, suggesting that the Z-line of the sarcomere is apparently preserved, despite the absence of telethonin. Ultrastructural analysis confirmed the integrity of the sarcomeric architecture. The possible interaction of telethonin with other proteins responsible for several forms of neuromuscular disorders was also analyzed. Telethonin was clearly present in the rods in nemaline myopathy (NM) muscle fibers, confirming its localization to the Z-line of the sarcomere. Muscle from patients with absent telethonin showed normal expression for the proteins dystrophin, sarcoglycans, dysferlin, and calpain-3. Additionally, telethonin showed normal localization in muscle biopsies from patients with LGMD2A, LGMD2B, sarcoglycanopathies, and Duchenne muscular dystrophy (DMD). Therefore, the primary deficiency of calpain-3, dysferlin, sarcoglycans, and dystrophin do not seem to alter telethonin expression.

Genetic diseases of muscle

In the last twenty years, the genetic basis for most of the inherited myopathies and muscular dystrophies has been unveiled. Diseases have been found to result from loss of function of structural components of the muscle basal lamina (e.g., MCD1A), sarcolemma (e.g., the sarcoglycanopathies), nucleus (e.g., EDMD) and sarcomere (e.g., the nemaline myopathies). A few have been associated with abnormalities in the genes for muscle enzymes (e.g., calpain and fukutin). Alternate mechanisms of pathogenesis have also recently been suggested by mutations lying outside of coding regions, such as the "field effect" of chromosomal mutations in DM2. In the future, we will likely identify the genes responsible for the remaining disorders, including many of the distal myopathies. In addition, we may also find skeletal muscle diseases associated with some of the presently non-implicated muscle proteins: syntropin, dystrobrevin, epsilon-sarcoglycan and sarcospan. The next steps may be to identify and understand the relationship of modifier genes producing the phenotypic heterogeneity of many of these diseases and to characterize those and other targets for therapeutic intervention, whether by gene therapy or by pharmacological treatment.

Genetics of population isolates

Genetic isolates, as shown empirically by the Finnish, Old Order Amish, Hutterites, Sardinian and Jewish communities among others, represent a most important and powerful tool in genetically mapping inherited disorders. The main features associated with that genetic power are the existence of multigenerational pedigrees which are mostly descended from a small number of founders a short number of generations ago, environmental and phenotypic homogeneity, restricted geographical distribution, the presence of exhaustive and detailed records correlating individuals in very well ascertained pedigrees, and inbreeding as a norm. On the other hand, the presence of a multifounder effect or admixture among divergent populations in the founder time (e.g. the Finnish and the Paisa community from Colombia) will theoretically result in increased linkage disequilibrium among adjacent loci. The present review evaluates the historical context and features of some genetic isolates with emphasis on the basic population genetic concepts of inbreeding and genetic drift, and also the state-of-the-art in mapping traits, both Mendelian and complex, on genetic isolates.

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.

Dysferlin expression after normal myoblast transplantation in SCID and in SJL mice

Limb girdle muscular dystrophy type 2B form and Miyoshi myopathy are both caused by mutations in the recently cloned gene dysferlin. In the present study, we have investigated whether cell transplantation could permit dysferlin expression in vivo. Two transplantation models were used: SCID mice transplanted with normal human myoblasts, and SJL mice, the mouse model for limb girdle muscular dystrophy type 2B and Miyoshi myopathy, transplanted with allogeneic primary mouse muscle cell cultures expressing the beta-galactosidase gene under control of a muscle promoter of Troponin I. FK506 immunosuppression was used in the non-compatible allogeneic model. One month after transplantation, human and mouse dysferlin proteins were detected in all transplanted SCID and SJL muscles, respectively. Co-localization of dysferlin and human dystrophin or beta-galactosidase-positive fibers was observed following the transplantation of myoblasts. Dysferlin proteins were monitored by immunocytochemistry and Western blot. The number of dysferlin-positive fibers was 40-50% and 20-30% in SCID and SJL muscle sections, respectively. Detection of dysferlin in both SCID mice and dysferlin-deficient SJL mouse shows that myoblast transplantation permits the expression of the donor dysferlin protein.

A biologia molecular contribuindo para a compreensão e a prevenção das doenças hereditárias

O fim do seqüenciamento do genoma humano levanta inúmeras questões: Como o projeto genoma humano vai influenciar nossas vidas? Como a medicina tem se beneficiado do estudo dos genes? Quais são as aplicações práticas imediatas e o que se espera para o futuro? Quais são as implicações éticas? Este capítulo ilustra como as doenças genéticas têm contribuído para a compreensão do genoma humano. Ajuda-nos a entender como nossos genes funcionam quando normais e por que causam doenças quando alterados. Do ponto de vista prático, o estudo dos genes tem permitido o diagnóstico molecular para um número crescente de patologias, o que é fundamental para evitar outros exames invasivos, identificar casais em risco, e prevenir o nascimento de novos afetados. Além disso, discute-se quais são as perspectivas futuras em relação ao tratamento destas e de outras patologias genéticas incluindo a clonagem para fins terapêuticos e a utilização de células-tronco. Finalmente aborda as implicações éticas relacionadas ao uso de testes genéticos. Os benefícios de cada teste, principalmente para doenças de início tardio para as quais ainda não há tratamento, têm que ser discutidos exaustivamente com os consulentes antes de sua aplicação.

The ABC's of limb-girdle muscular dystrophy: alpha-sarcoglycanopathy, Bethlem myopathy, calpainopathy and more

Limb-girdle muscular dystrophy is a class of disorders encompassing many forms of this disease. Variation exists between the inheritance patterns, genes responsible, course of disease and symptoms, with the cohesive factor among these disorders being the predominance of proximal muscle weakness. Here we review each form of limb-girdle muscular dystrophy with attention to molecular genetics, clinical features, inheritance, and diagnostic issues pertaining to each primary genetic cause.

Calpain 3 gene mutations: genetic and clinico-pathologic findings in limb-girdle muscular dystrophy

Mutations in the calpain 3 gene have been proven to be responsible for limb-girdle muscular dystrophy (LGMD) type 2A. To determine the incidence and genotypes of the calpain 3 (p94) gene mutations in Japanese LGMD patients, we sequenced the gene in 80 patients with clinical characteristics of autosomal recessive or sporadic LGMD. We identified 13 distinct pathogenic mutations in 21 patients (26%), including seven missense mutations, four splice-site mutations and two insertions in which six were novel mutations. Among the 21 patients, 15 (71%) had three types of the common missense (G233V, R461C, D707G) and one insertion (1795-1796insA) mutation. The patients had slowly progressive muscle weakness with age of onset of the disease varying from 6 to 52 years, averaging 20.9. The most striking pathologic findings were the presence of lobulated fibers in 14 patients, especially in the advanced stages. Differing from Duchenne and Becker muscular dystrophy, opaque (hypercontracted) fibers were very rarely seen. These findings may be helpful in establishing diagnostic screening strategies in Japanese LGMD patients.

Dysferlin protein analysis in limb-girdle muscular dystrophies

Dysferlin is the protein product of the DYSF gene mapped at 2p31, which mutations cause limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy. To date, nine autosomal recessive forms (AR-LGMD) have been identified: four genes, which code for the sarcoglycan glycoproteins, are associated with both mild and severe forms, the sarcoglycanopathies (LGMD2C, 2D, 2E and 2F). The other five forms, usually causing a milder phenotype are LGMD2A (calpain 3), LGMD2B (dysferlin), LGMD2G (telethonin), LGMD2H (9q31-11), and LGMD21 (19q13.3). We studied dysferlin expression in a total of 176 patients, from 166 LGMD families: 12 LGMD2B patients, 70 with other known forms of muscular dystrophies (LGMD2A, sarcoglycanopathies, LGMD2G), in an attempt to assess the effect of the primary gene-product deficiency on dysferlin. In addition, 94 still unclassified LGMD families were screened for dysferlin deficiency. In eight LGMD2B patients from five families, no dysferlin was observed in muscle biopsies, both through immunofluorescence (IF) and Western blot methodologies, while in two families, a very faint band was detected. Both patterns, negative or very faint bands, were concordant in patients belonging to the same families, suggesting that dysferlin deficiency is specific to LGMD2B. Myoferlin, the newly identified homologue of dysferlin was studied for the first time in LGMD2B patients. Since no difference was observed between patients mildly and severely affected, this protein do not seem to modify the phenotype in the present dysferlin-deficient patients. Dystrophin, sarcoglycans, and telethonin were normal in all LGMD2B patients, while patients with sarcoglycanopathies (2C, 2D, and 2E), LGMD2A, LGMD2G, and DMD showed the presence of a normal dysferlin band by Western blot and a positive pattern on IF. These data suggest that there is no interaction between dysferlin and these proteins. However, calpain analysis showed a weaker band in four patients from two families with intra-familial concordance. Therefore, this secondary deficiency of calpain in LGMD2B families, may indicate an interaction between dysferlin and calpain in muscle. Dysferlin was also present in cultured myotubes, in chorionic villus, and in the skin. Dysferlin deficiency was found in 24 out of a total of 166 Brazilian AR-LGMD families screened for muscle proteins (approximately 14%), thus representing the second most frequent known LGMD form, after calpainopathy, in our population.

Mutations in the caveolin-3 gene: When are they pathogenic?

Limb-girdle muscular dystrophies (LGMD) are a heterogeneous group of genetic disorders usually with autosomal recessive (AR) inheritance and, less often, displaying autosomal dominant (AD) inheritance. Mutations in the caveolin-3 gene (CAV-3) associated with a reduction of protein expression cause AD-LGMD1C muscular dystrophy. Based on a previous study in the American and Brazilian population, it has been suggested that CAV-3 mutations might also cause AR-LGMD. Here we report the analysis of the CAV-3 gene in 61 additional Brazilian LGMD patients and 100 additional Brazilian normal controls. Two rare G55S and C71W missense changes previously detected only in LGMD patients (and not detected in 100 normal controls from the American population) were now found in normal Brazilian controls. In addition, we have identified a novel R125H missense change in one LGMD female patient that was also found in two of her unaffected siblings. These observations, together with the normal immunofluorescence caveolin pattern in the muscle biopsy from two patients with the G55W and R125H changes in the CAV-3 gene suggest that the G55S, C71W, and R125H polymorphisms, on their own, are not sufficient to produce the pathology.

A new dysferlin gene mutation in two Japanese families with limb-girdle muscular dystrophy 2B and Miyoshi myopathy

We found a new dysferlin gene mutation in two Japanese families, one with limb-girdle muscular dystrophy 2B and the other with Miyoshi myopathy. All patients in the limb-girdle muscular dystrophy 2B family showed apparent proximal dominant muscle atrophy and weakness, whereas a patient with Miyoshi myopathy in the second family showed distal muscle involvement at an early stage. The common clinical feature of all patients in both families was preferential involvement of calf muscles rather than the tibialis anterior muscle, which was confirmed by muscle computed tomography scan. All patients in both families shared the same homozygous alleles for chromosome 2p13 markers, and dysferlin gene analysis revealed a novel missense mutation, a G to A transition at nt 5882, which changed aspartic acid to asparagine at codon 1837. Allele-specific polymerase chain reaction analysis was used for confirmation of the mutation and for genotype analysis of the family members.

Skeletal muscle-specific calpain, p94, and connectin/titin: their physiological functions and relationship to limb-girdle muscular dystrophy type 2A

The skeletal muscle-specific calpain homologue, p94 (also called calpain 3), is essential for normal muscle function. A mutation of the p94 gene causes limb-girdle muscular dystrophy type 2A (LGMD2A), which is one type of autosomal recessive inherited disease characterized by progressive muscular degeneration. In myofibrils, p94 specifically binds to connectin/titin, and the activity of p94 is probably suppressed by this binding. Thus, we postulate that a signal transduction pathway exists, involving p94 and connectin/titin to modulate functions of skeletal muscle, and LGMD2A occurs when this signalling pathway is not properly regulated by p94. LGMD2A mutants of p94 also reveal significant information on the factors that relate structure to function in this molecule.

Strategy for mutation analysis in the autosomal recessive limb-girdle muscular dystrophies

We describe a strategy for molecular diagnosis in the autosomal recessive limb-girdle muscular dystrophies, a highly heterogeneous group of inherited muscle-wasting diseases. Genetic mutation analysis is directed by immunoanalysis of muscle biopsies using antibodies against a panel of muscular dystrophy-associated proteins. Performing the molecular analysis in this way greatly increases the chance that mutations will be found in the first gene examined. The use of this strategy can significantly decrease the time involved in determining the genetic fault in a patient with a clinical diagnosis of recessive limb-girdle muscular dystrophy, as well as having a feedback effect, which is useful in helping clinicians to identify subtle clinical differences between the subtypes of the disease. The use of this approach has so far helped us to identify mutations in ten sarcoglycanopathy (limb-girdle muscular dystrophy 2C-2F) patients, and seven calpainopathy (limb-girdle muscular dystrophy 2A) patients.

Evaluation of the dystrophin-glycoprotein complex, alpha-actinin, dysferlin and calpain 3 in an autosomal recessive muscular dystrophy in Labrador retrievers

Labrador retrievers suffer from an autosomal recessive muscular dystrophy of unknown aetiology. Dogs affected with this disease develop generalized weakness associated with severe, generalized skeletal muscle atrophy and mild elevations in creatine kinase in the first few months of life. The severity of signs tends to progress over the first year of life but can vary from mild exercise intolerance to non-ambulatory tetraparesis. Beyond 1 year of age, the signs usually stabilize and although muscle mass does not increase, affected dogs' strength may improve slightly. The pathological changes present on muscle biopsy include marked variation in muscle fibre size with hypertrophied and round atrophied fibres present. There is an increased number of fibres with central nuclei and split fibres can be seen. It has been suggested that the disorder is a model for limb-girdle muscular dystrophy. In recent years, mutations in genes encoding the proteolytic enzyme, calpain 3, a novel protein named dysferlin, and components of the dystrophin-glycoprotein complex have been identified as causes of autosomal recessive limb-girdle muscular dystrophy. We have evaluated these proteins in normal dogs and in three Labrador retrievers with autosomal recessive muscular dystrophy using immunohistochemistry and Western blot analysis on frozen skeletal muscle. The results demonstrate that dystrophin, the sarcoglycans, alpha-actinin, dysferlin and calpain 3 are present in the normal and affected dogs. We conclude that this autosomal recessive muscular dystrophy is not due to a deficiency of alpha-actinin, or any of the known autosomal recessive limb-girdle muscular dystrophy proteins, although we cannot rule out a malfunction of any of these proteins.

Polydom: a secreted protein with pentraxin, complement control protein, epidermal growth factor and von Willebrand factor A domains

To identify extracellular proteins with epidermal growth factor (EGF) domains that are potentially involved in the control of haemopoiesis, we performed degenerate reverse-transcriptase-mediated PCR on the murine bone-marrow stromal cell line MS-5 and isolated a new partial cDNA encoding EGF-like domains related to those in the Notch proteins. Cloning and sequencing of the full-length cDNA showed that it encoded a new extracellular multi-domain protein that we named polydom. This 387 kDa mosaic protein contained a signal peptide followed by a new association of eight different protein domains, including a pentraxin domain and a von Willebrand factor type A domain, ten EGF domains, and 34 complement control protein modules. The human polydom mRNA is strongly expressed in placenta, its expression in the other tissues being weak or undetectable. The particular multidomain structure of the encoded protein suggests an important biological role in cellular adhesion and/or in the immune system.

Limb-girdle muscular dystrophy: one gene with different phenotypes, one phenotype with different genes

Among 14 limb-girdle muscular dystrophy genes that have been mapped, 10 (three autosomal dominant and seven autosomal recessive) have so far had their product identified. This review will focus on the most recent data in the field and on our own experience of more than 200 patients studied with autosomal recessive-limb-girdle muscular dystrophy, classified from calpainopathy to telethoninopathy. Genotype: phenotype correlations in this highly heterogeneous group show a similar clinical course among patients with different forms, whereas a discordant phenotype may be seen in unrelated patients or in affected sibs carrying the same mutation. Understanding such similarities or differences remains a major challenge. It will depend on future knowledge of gene-protein functions, on protein interactions and on identifying modifying genes and other factors underlying clinical variability.

Molecular basis of muscular dystrophies

Muscular dystrophies represent a heterogeneous group of disorders, which have been largely classified by clinical phenotype. In the last 10 years, identification of novel skeletal muscle genes including extracellular matrix, sarcolemmal, cytoskeletal, cytosolic, and nuclear membrane proteins has changed the phenotype-based classification and shed new light on the molecular pathogenesis of these disorders. A large number of genes involved in muscular dystrophy encode components of the dystrophin-glycoprotein complex (DGC) which normally links the intracellular cytoskeleton to the extracellular matrix. Mutations in components of this complex are thought to lead to loss of sarcolemmal integrity and render muscle fibers more susceptible to damage. Recent evidence suggests the involvement of vascular smooth muscle DGC in skeletal and cardiac muscle pathology in some forms of sarcoglycan-deficient limb-girdle muscular dystrophy. Intriguingly, two other forms of limb-girdle muscular dystrophy are possibly caused by perturbation of sarcolemma repair mechanisms. The complete clarification of these various pathways will lead to further insights into the pathogenesis of this heterogeneous group of muscle disorders.