Autosomal Dominant Limb-girdle Dystrophy Research Articles

CRISPR-Cas9 editing of a TNPO3 mutation in a muscle cell model of limb-girdle muscular dystrophy type D2

A single-nucleotide deletion in the stop codon of the nuclear import receptor transportin-3 (TNPO3), also involved in human immunodeficiency virus type 1 (HIV-1) infection, causes the ultrarare autosomal dominant disease limb-girdle muscular dystrophy D2 (LGMDD2) by extending the wild-type protein. Here, we generated a patient-derived invitro model of LGMDD2 as an immortalized myoblast cell line carrying the TNP O 3 mutation. The cell model reproduced critical molecular alterations seen in patients, such as TNP O 3 overexpression, defects in terminal muscle markers, and autophagy overactivation. Correction of the TNP O 3 mutation via CRISPR-Cas9 editing caused a significant reversion of the pathological phenotypes in edited cells, including a complete absence of the mutant TNPO3 protein, as detected with a polyclonal antibody specific against the abnormal 15-aa peptide. Transcriptomic analyses found that 15% of the transcriptome was differentially expressed in model myotubes. CRISPR-Cas9-corrected cells showed that 44% of the alterations were rescued toward normal levels. MicroRNAs (miRNAs) analyses showed that around 50% of miRNAs with impaired expression because of the disease were recovered on the mutation edition. In summary, this work provides proof of concept of the potential of CRISPR-Cas9-mediated gene editing of TNP O 3 as a therapeutic approach and describes critical reagents in LGMDD2 research.

Caveolin 3 suppresses phosphorylation-dependent activation of sarcolemmal nNOS

Mutations of the caveolin 3 gene cause autosomal dominant limb-girdle muscular dystrophy (LGMD)1C. In mice, overexpression of mutant caveolin 3 leads to loss of caveolin 3 and results in myofiber hypotrophy in association with activation of neuronal nitric oxide synthase (nNOS) at the sarcolemma. Here, we show that caveolin 3 directly bound to nNOS and suppressed its phosphorylation-dependent activation at a specific residue, Ser1412 in the nicotinamide adenine dinucleotide phosphate (NADPH)−flavin adenine dinucleotide (FAD) module near the C-terminus of the reduction domain, in vitro. Constitutively active nNOS enhanced myoblast fusion, but not myogenesis, in vitro. Phosphorylation-dependent activation of nNOS occurred in muscles from caveolin 3-mutant mice and LGMD1C patients. Mating with nNOS-mutant mice exacerbated myofiber hypotrophy in the caveolin 3-mutant mice. In nNOS-mutant mice, regenerating myofibers after cardiotoxin injury became hypotrophic with reduced myoblast fusion. Administration of NO donor increased myofiber size and the number of myonuclei in the caveolin 3-mutant mice. Exercise also increased myofiber size accompanied by phosphorylation-dependent activation of nNOS in wild-type and caveolin 3-mutant mice. These data indicate that caveolin 3 inhibits phosphorylation-dependent activation of nNOS, which leads to myofiber hypertrophy via enhancing myoblast fusion. Hypertrophic signaling by nNOS phosphorylation could act in a compensatory manner in caveolin 3-deficient muscles.

LGMD D2 TNPO3-Related: From Clinical Spectrum to Pathogenetic Mechanism.

Limb-girdle muscular dystrophies (LGMDs) are clinically and genetically heterogeneous diseases presenting with a wide clinical spectrum. Autosomal dominant LGMDs represent about 10–15% of LGMDs and include disorders due to defects of DNAJB6, transportin-3 (TNPO3), HNRNPDL, Calpain-3 (CAPN3), and Bethlem myopathy. This review article aims to describe the clinical spectrum of LGMD D2 TNPO3-related, a rare disease due to heterozygous mutation in the TNPO3 gene. TNPO3 encodes for transportin-3, which belongs to the importin beta family and transports into the nucleus serine/arginine-rich (SR) proteins, such as splicing factors, and HIV-1 proteins, thus contributing to viral infection. The purpose of this review is to present and compare the clinical features and the genetic and histopathological findings described in LGMD D2, performing a comparative analytical description of all the families and sporadic cases identified. Even if the causative gene and mutations of this disease have been identified, the pathogenic mechanisms are still an open issue; therefore, we will present an overview of the hypotheses that explain the pathology of LGMD D2 TNPO3-related.

A novel pathogenic variant in TNPO3 in a Hungarian family with limb-girdle muscular dystrophy 1F

Limb-girdle muscular dystrophies (LGMDs) are a group of genetically heterogeneous muscular diseases that predominantly affect the proximal muscles. Pathogenic variants in TNPO3 have been associated with a rare, autosomal dominant limb-girdle muscular dystrophy 1F (LGMD1F) in a large Italian-Spanish family and an isolated LGMD1F case. Here we present two individuals from a Hungarian family with an early-onset, slowly progressive muscular dystrophy. Both the female proband and her affected son had delayed early motor milestones including first walking at 14 months and 18 months, respectively. Both present with progressive weakness of facial, bulbar, axial, and distal muscles especially of the lower extremities. Electromyography indicated myogenic damage and muscle biopsy from the proband showed myopathic alterations with sarcoplasmic masses and signs of mitochondrial dysfunction. Exome sequencing of the female proband identified a novel c.2767delC p.(Arg923AspfsTer17) variant in TNPO3. Sanger sequencing confirmed the presence of the TNPO3 variant in the affected son; the unaffected son did not have the variant. The identification of the c.2767delC variant further supports the clinical significance of TNPO3 and expands the clinical spectrum of TNPO3-associated LGMD1F.

A novel TTN deletion causes Autosomal Dominant Limb-Girdle Muscular Dystrophy with Dilated Cardiomyopathy (P5.4-001)

A novel TTN deletion causes Autosomal Dominant Limb-Girdle Muscular Dystrophy with Dilated Cardiomyopathy (P5.4-001)

Autosomal dominant calpainopathy due to heterozygous CAPN3 C.643_663del21.

A calpain-3 (CAPN3) gene heterozygous deletion (c.643_663del21) was recently linked to autosomal dominant (AD) limb-girdle muscular dystrophy. However, the possibility of digenic disease was raised. We describe 3 families with AD calpainopathy carrying this isolated mutation. Probands heterozygous for CAPN3 c.643_663del21 were identified by targeted next generation or whole exome sequencing. Clinical findings were collected for probands and families. Calpain-3 muscle Western blots were performed in 3 unrelated individuals. Probands reported variable weakness in their 40s or 50s, with myalgia, back pain, or hyperlordosis. Pelvic girdle muscles were affected with adductor and hamstring sparing. Creatine kinase was normal to 1,800 U/L, independent of weakness severity. Imaging demonstrated lumbar paraspinal muscle atrophy. Electromyographic findings and muscle biopsies were normal to mildly myopathic. Muscle calpain-3 expression was reduced. This study provides further evidence for AD calpainopathy associated with CAPN3 c.643_663del21. No pathogenic variants in other genes known to cause myopathy were detected. Muscle Nerve 57: 679-683, 2018.

Limb-girdle muscular dystrophy 1F is caused by a microdeletion in the transportin 3 gene

Whole genome sequencing strategy allowed identifying the gene responsible for autosomal dominant limb-girdle muscular dystrophy 1F, which was previously linked to locus 7q32.1-32.2. A large Spanish family spanning six generations with limb girdle muscular weakness and distal involvement was find to present a mutation in the stop codon of TNPO3 gene (c.2771delA). The mutation segregates with the clinical phenotype, and is absent in healthy relatives of the family as well as in genomic sequence databases. Histological abnormalities of the nuclei and altered TNPO3 expression assessed in muscle biopsy of the patients indicate impaired TNPO3 function. TNPO3 encodes transportin-3, a serine/arginine rich protein carrier through nuclear membrane. The function of transportin-3 in skeletal muscle has not been thoroughly characterized. The identification of this mutation as the cause of autosomal dominant limb-girdle muscular dystrophy highlights the importance of defects of nuclear envelope proteins as causes of inherited myopathies[1].

L.I.1: Autosomal dominant limb-girdle muscular dystrophies

The first gene identified in the group of autosomal dominant forms of LGMD was CAV3 more than 15 years ago, although families with caveolinopathy LGMD1C have remained very rare in the total group of LGMD families. In 2000 two more genes were identified: MYOT in LGMD1A and LMNA in LGMD1B. The LGMD phenotype of Myotilinopathy has also remained very rare, whereas mutations in MYOT much more frequently cause late onset distal myopathy with the characteristic myofibrillar pathology. Laminopathies however are not rare and present with a large range of different phenotypes. Pure LGMD may be less common than autosomal dominant EDMD and these two phenotypes may variably be present even within the families. The chromosomal locus definitions of 7q36 and 6q23 linked LGMD1D and LGMD1E have been mixed up constantly over the years, but since the original family linked to 6q23 recently proved to be desminopathy, there is no 6q23 linked autosomal dominant LGMD anymore and thus the 7q36 linked disease is LGMD1D, which also corresponds to the HGNC definition. The mutated gene in LGMD1D encodes a ubiquitously expressed co-chaperone DNAJB6. The latest gene identification was TNPO3 responsible for LGMD1F. One very interesting feature with this collection of dominant LGMD genes is that there is no obvious common denominator for the functions of the proteins: Myotilin is a Z-disc protein, Lamin A/C is in the nuclear envelope, Caveolin-3 in the caveolae of the sarcolemma, DNAJB6 is a component of the chaperonal maintenance machinery, and Transportin-3 in the nuclear membrane pores. Other autosomal dominant LGMD families still await the identification of the responsible gene defects. The first gene identified in the group of autosomal dominant forms of LGMD was CAV3 more than 15 years ago, although families with caveolinopathy LGMD1C have remained very rare in the total group of LGMD families. In 2000 two more genes were identified: MYOT in LGMD1A and LMNA in LGMD1B. The LGMD phenotype of Myotilinopathy has also remained very rare, whereas mutations in MYOT much more frequently cause late onset distal myopathy with the characteristic myofibrillar pathology. Laminopathies however are not rare and present with a large range of different phenotypes. Pure LGMD may be less common than autosomal dominant EDMD and these two phenotypes may variably be present even within the families. The chromosomal locus definitions of 7q36 and 6q23 linked LGMD1D and LGMD1E have been mixed up constantly over the years, but since the original family linked to 6q23 recently proved to be desminopathy, there is no 6q23 linked autosomal dominant LGMD anymore and thus the 7q36 linked disease is LGMD1D, which also corresponds to the HGNC definition. The mutated gene in LGMD1D encodes a ubiquitously expressed co-chaperone DNAJB6. The latest gene identification was TNPO3 responsible for LGMD1F. One very interesting feature with this collection of dominant LGMD genes is that there is no obvious common denominator for the functions of the proteins: Myotilin is a Z-disc protein, Lamin A/C is in the nuclear envelope, Caveolin-3 in the caveolae of the sarcolemma, DNAJB6 is a component of the chaperonal maintenance machinery, and Transportin-3 in the nuclear membrane pores. Other autosomal dominant LGMD families still await the identification of the responsible gene defects.

P.5.10 Clinical and ultrastructural changes in transportinopathy

Muscle histopathological, ultrastructural and genetic features of a large Italian-Spanish family with autosomal dominant LGMD, previously mapped to 7q32.1–32.2 (LGMD1F) were studied in 3 biopsies. We collected the clinical history in 19 of 60 patients; muscle biopsy histopathology was investigated in one pair of affected patients (mother 1 biopsy, her daughter 2 consecutive biopsies at 9 and 22 years). We observed that the age of onset varied from 2 to 35 years, and occurred either in upper or in the lower girdle; in 14 cases there was hypotrophy both in proximal upper and in lower extremities in calf muscles. The severity was not increased in successive generations. Unreported clinical findings were arachnodactyly, dysphagia and dysarthria. Moreover, we noticed a discrepancy between the clinical severity and muscle biopsy involvement: the daughter has a more severe clinical course, the first biopsy had only type 1 fiber atrophy while increased fiber atrophy was observed in the second biopsy. The mother has a compromised muscle histopathology (more muscle fiber variation, and autophagic changes by acid phosphatase stain). An abnormal sarcomeric assembly is the cause of progressive atrophy and myofiber loss. Electron microscopy revealed accumulation of myofibrillar bodies in muscle fibers. Accumulation of desmin and myotilin and p62-positive aggregates was observed. A defect in transportin-3 gene has been found to be the cause of this disease, which represents a new mechanism of dominant myopathy. Our morphological and ultrastructural data seems to suggest a phenotype similar to myofibrillar disease; however, autophagosomes were also present. It is possible that SR protein cannot migrate or be transported in- and out-of the nuclear membrane.

A Family With 2 Different Hereditary Diseases Leading to Early Cardiac Involvement

Autosomal dominant limb-girdle muscular dystrophy type 1B (LGMD 1B) is caused by mutations in the LMNA gene. The disorder is associated with potentially fatal cardiac arrhythmias. Brugada syndrome (BS) is an autosomal dominant channelopathy linked to mutations in the SCN5A gene. BS is also associated with increased risk of sudden cardiac death. We reported a family in which a novel gene mutation, a missense mutation (c.80C>T) in exon 1 of the LMNA gene causing autosomal dominant LGMD 1B, occurred in association with SCN5A gene mutation causing BS. After the diagnosis of BS, 4 patients received implantable cardioverter-defibrillator therapy. Eight members of the family deceased at early age before the diagnosis. We emphasized the co-occurrence of 2 different conditions predisposing to sudden cardiac death: LGMD 1B caused by a novel mutation and BS.

A case of heart failure complicated with autosomal dominant limb-girdle muscular dystrophy successfully treated with cardiac resynchronization therapy

A case of heart failure complicated with autosomal dominant limb-girdle muscular dystrophy successfully treated with cardiac resynchronization therapy

Exome Analysis of Two Limb-Girdle Muscular Dystrophy Families: Mutations Identified and Challenges Encountered

The molecular diagnosis of muscle disorders is challenging: genetic heterogeneity (>100 causal genes for skeletal and cardiac muscle disease) precludes exhaustive clinical testing, prioritizing sequencing of specific genes is difficult due to the similarity of clinical presentation, and the number of variants returned through exome sequencing can make the identification of the disease-causing variant difficult. We have filtered variants found through exome sequencing by prioritizing variants in genes known to be involved in muscle disease while examining the quality and depth of coverage of those genes. We ascertained two families with autosomal dominant limb-girdle muscular dystrophy of unknown etiology. To identify the causal mutations in these families, we performed exome sequencing on five affected individuals using the Agilent SureSelect Human All Exon 50 Mb kit and the Illumina HiSeq 2000 (2×100 bp). We identified causative mutations in desmin (IVS3+3A>G) and filamin C (p.W2710X), and augmented the phenotype data for individuals with muscular dystrophy due to these mutations. We also discuss challenges encountered due to depth of coverage variability at specific sites and the annotation of a functionally proven splice site variant as an intronic variant.

Nuclear lamins

ADLD= : adult-onset autosomal dominant leukodystrophy; CMT= : Charcot-Marie-Tooth; EDMD= : Emery-Dreifuss muscular dystrophy; LAP= : lamin-associated polypeptide; LBR= : lamin B receptor; LGMD1B= : autosomal dominant limb-girdle muscular dystrophy The nuclear envelope is the interface between the nucleus and the rest of the cell and consists of inner and outer nuclear membranes. The nuclear lamina underlies the inner nuclear membrane and is an essential structural element of the nuclear envelope. The nuclear lamina maintains the nuclear architecture and regulates DNA replication and chromatin organization. The major components of the nuclear lamina are the nuclear lamins, including lamin A/C and lamin B. Lamins interact with several other inner nuclear proteins, such as emerin; these interactions are critical for the functional organization of chromatin, transport across the nuclear envelope, and transmission of mechanical signals to the nucleus. Mutations in genes encoding lamins and their associated proteins cause a wide spectrum of diseases called “laminopathies.” Mutations affecting lamin A or associated proteins, such as emerin, produce Emery-Dreifuss muscular dystrophy (EDMD). LMNA mutations also produce autosomal dominant limb-girdle muscular dystrophy (LGMD1B) and Charcot-Marie-Tooth (CMT) disease type 2B1. Duplication in LMNB1 , encoding lamin B1, causes autosomal dominant leukodystrophy. Lamin mutations have also been linked to cardiomyopathy, lipodystrophy, and accelerated aging disorders. The functional organization of the nuclear envelope and the wide spectrum of laminopathies have been the subject of several recent reviews.1,–,7 The principal components of the nuclear envelope are the inner and outer nuclear membranes, separated by the perinuclear space4,8 (figure). The outer nuclear membrane is contiguous with and functionally related …

G.P.45 A family of autosomal dominant limb-girdle muscular dystrophy with rimmed vacuole

Limb-girdle muscular dystrophy (LGMD) is a descriptive term that encompasses childhood- or adult-onset muscular dystrophies, not characterized as dystrophinopathy. While most cases of LGMD follow autosomal recessive inheritance, many families with distinct autosomal dominant (AD) pattern have been reported. Causative genes are known for three of the AD LGMDs, which are myotilin, lamin A/C, and caveolin-3. For the other AD LGMDs, loci by linkage analysis are identified. We found a family of AD LGMD. The affected are 11, both male and female, out of 37 family members through three successive generations without consanguineous marriage. Limb weakness typically starts during childhood. The affected has never been good at sports. They have difficulty lifting heavy objects or climbing stairs, after which pain follows in the used limbs. On examination, mild proximal limb muscle atrophy was noted with moderate calf pseudohypertrophy. Contracture was not evident. They showed Gower’s sign and waddling gait. Distal muscle power was largely preserved compared to proximal parts. Most interestingly, all of the affected had dysphagia that it was a rule to assume chin tuck posture on swallowing. They also had nasal voice with drooping soft palate, but did not have other difficulty in articulation. On muscle biopsy, scattered rimmed vacuoles were noted upon general dystrophic features. Immunohistochemistry of dystrophin, sarcoglycans, dysferlin, and dystroglycans did not reveal abnormality. Distinctive clinical features of previously characterized LGMD like contracture or mounding do not match with this family. Based upon inheritance pattern and pathologic finding, we sequenced myotilin (TTID), but failed to prove any mutation. Very likely this family with unique clinical/pathologic features are due to mutation in a novel gene. Extensive search for the causative gene including exome sequencing and/or linkage analysis is warranted for genetic diagnosis and therapeutic opportunities.

G.P.44 Spectrum of mutations identified in the cohort of Czech LGMD patients

Limb girdle muscular dystrophies (LGMDs) represent a group of clinically and genetically heterogeneous disorders predominantly affecting shoulder and pelvic girdles. To date, 15 forms (2A-N) of autosomal recessive (AR) and eight forms (1A-H) of autosomal dominant LGMDs have been described. LGMD2A is the most frequent form of LGMD in many European countries, and is caused by mutations in the CAPN3 gene that encodes a muscle specific protease, calpain-3. Besides LGMD2A, we perform molecular genetic diagnostics of LGMD2I, LGMD2D, and LGMD2L caused by mutations in genes encoding fukutin-related protein (FKRP), alpha-sarcoglycan (SGCA) and anoctamin-5 (ANO5). Based on the results of clinical assessment and histopathological examination of muscle biopsies (including protein analysis using immunohistochemistry and immunoblotting), the mutational analysis of the CAPN3, FKRP, SGCA, and ANO5 genes was performed at the mRNA level (using reverse transcription-PCR-direct sequencing) and/or at the DNA level (using PCR-direct sequencing) in a cohort of Czech patients with a preliminary diagnosis of LGMD. In total, we screened 230 unrelated patients and mutations associated with the disease were determined in 70 of them (30.4%). Mutations in the CAPN3 gene were found in 55 patients, and LGMD2A was confirmed to represent the most frequent AR LGMD in the Czech Republic. The homozygous occurence of the most common mutation in the FKRP gene (p.Leu276Ile) associated with LGMD2I was determined in eight patients. Mutations in the SGCA and ANO5 genes were detected in 5 LGMD2D and 2 LGMD2L patients, respectively. This work was funded by the project “CEITEC – Central European Institute of Technology” (CZ.1.05/1.1.00/02.0068).

An inhibitor of transforming growth factor beta type I receptor ameliorates muscle atrophy in a mouse model of caveolin 3-deficient muscular dystrophy

Skeletal muscle expressing Pro104Leu mutant caveolin 3 (CAV3P104L) in mouse becomes atrophied and serves as a model of autosomal dominant limb-girdle muscular dystrophy 1C. We previously found that caveolin 3-deficient muscles showed activated intramuscular transforming growth factor beta (TGF-β) signals. However, the cellular mechanism by which loss of caveolin 3 leads to muscle atrophy is unknown. Recently, several small-molecule inhibitors of TGF-β type I receptor (TβRI) kinase have been developed as molecular-targeting drugs for cancer therapy by suppressing intracellular TGF-β1, -β2, and -β3 signaling. Here, we show that a TβRI kinase inhibitor, Ki26894, restores impaired myoblast differentiation in vitro caused by activin, myostatin, and TGF-β1, as well as CAV3P104L. Oral administration of Ki26894 increased muscle mass and strength in vivo in wild-type mice, and improved muscle atrophy and weakness in the CAV3P104L mice. The inhibitor restored the number of satellite cells, the resident stem cells of adult skeletal muscle, with suppression of the increased phosphorylation of Smad2, an effector, and the upregulation of p21 (also known as Cdkn1a), a target gene of the TGF-β family members in muscle. These data indicate that both TGF-β-dependent reduction in satellite cells and impairment of myoblast differentiation contribute to the cellular mechanism underlying caveolin 3-deficient muscle atrophy. TβRI kinase inhibitors could antagonize the activation of intramuscular anti-myogenic TGF-β signals, thereby providing a novel therapeutic rationale for the alternative use of this type of anticancer drug in reversing muscle atrophy in various clinical settings.

Exome sequencing reveals DNAJB6 mutations in dominantly‐inherited myopathy

To identify the causative gene in an autosomal dominant limb-girdle muscular dystrophy (LGMD) with skeletal muscle vacuoles. Exome sequencing was used to identify candidate mutations in the studied pedigree. Genome-wide linkage was then used to narrow the list of candidates to a single disease-associated mutation. Additional pedigrees with dominant or sporadic myopathy were screened for mutations in the same gene (DNAJB6) using exome sequencing. Skeletal muscle from affected patients was evaluated with histochemistry and immunohistochemical stains for dystrophy-related proteins, SMI-31, TDP43, and DNAJB6. Exome analysis in 3 affected individuals from a family with dominant LGMD and vacuolar pathology identified novel candidate mutations in 22 genes. Linkage analysis excluded all variants except a Phe93Leu mutation in the G/F domain of the DNAJB6 gene, which resides within the LGMD locus at 7q36. Analysis of exome sequencing data from other pedigrees with dominant myopathy identified a second G/F domain mutation (Pro96Arg) in DNAJB6. Affected muscle showed mild dystrophic changes, vacuoles, and abnormal aggregation of proteins, including TDP-43 and DNAJB6 itself. Mutations within the G/F domain of DNAJB6 are a novel cause of dominantly-inherited myopathy. DNAJB6 is a member of the HSP40/DNAJ family of molecular co-chaperones tasked with protecting client proteins from irreversible aggregation during protein synthesis or during times of cellular stress. The abnormal accumulation of several proteins in patient muscle, including DNAJB6 itself, suggest that DNAJB6 function is compromised by the identified G/F domain mutations.

Endoplasmic reticulum stress response in P104L mutant caveolin-3 transgenic mice

Mutations in the caveolin-3 gene cause autosomal dominant limb-girdle muscular dystrophy 1C (LGMD1C). However, the precise molecular pathogenesis of caveolin-3-related muscular dystrophy remains uncertain. Here, we demonstrate the effect of gene dosage on the severity of the myopathic phenotype in P104L mutant caveolin-3 (mCav3(P104L)) transgenic mice, a model of LGMD1C. We analyzed the endoplasmic reticulum (ER) stress response in the transgenic mice and found upregulated transcription of the molecular chaperone, glucose-regulated protein (GRP78). Moreover, signaling downstream of GRP78 in the myofibers was activated toward apoptosis. However, terminal transferase dUTP nick end labeling assays detected a few apoptotic nuclei in transgenic mouse skeletal muscle, probably due to the transcriptional activation of Dad1, an anti-apoptotic factor in the ER. These findings suggest that the ER stress response caused by mCav3(P104L) plays a role in the pathogenesis of LGMD1C as a toxic gain of function effect.

Four new Finnish families with LGMD1D; refinement of the clinical phenotype and the linked 7q36 locus

The objective is to refine the clinical and morphological phenotype and the chromosomal region of interest, in the recently reported 7q36 linked autosomal dominant limb-girdle muscular dystrophy (LGMD1 D/E), by describing four new informative Finnish families. Examinations of the patients included serum CK, neurophysiological studies, cardiac and respiratory function examinations, muscle biopsies and muscle imaging. DNA samples were analyzed by genotyping. Patients in all families had very similar phenotypes with onset of muscle weakness in the pelvic girdle muscles between the fourth and sixth decade, later involvement of the shoulder girdle, and marked walking difficulties in the eighth decade. Muscle biopsies showed myopathic and/or dystrophic features. Genotyping confirmed linkage to the same locus at chromosome 7q36 in all families by one identically segregating haplotype. The linked region was narrowed down from <6.3 to <3.4 Mb. Sequencing of the genes in the area is ongoing, aiming to identify the genetic defect.

Novel LMNA Mutation Presenting as Severe Congenital Muscular Dystrophy

Mutations in the lamin A/C gene determine a heterogeneous group of congenital diseases, termed laminopathies, consisting of more than 15 phenotypes, including autosomal dominant Emery-Dreifuss muscular dystrophy and limb-girdle muscular dystrophy type 1B. Early onset in infancy has been described in these muscular dystrophies. Reported here is a 7-year-old male with congenital muscular dystrophy. Remarkably, muscle weakness and wasting affected predominantly axial muscles as well as proximal upper and distal lower extremities. The patient rapidly developed joint contractures and spine rigidity with the head only mildly flexed. Serum creatine kinase was moderately elevated. Muscle biopsy indicated a dystrophic pattern with normal immunochemical findings. A novel, de novo missense substitution p.Asn39Tyr within the lamin A/C gene confirmed the diagnosis of a laminopathy. This report broadens the spectrum of lamin A/C gene mutations and illustrates the phenotypic variability of laminopathies with early onset congenital muscular dystrophy. Mutations in the lamin A/C gene should be sought in any infant with dystrophic features and normal tissue immunochemical studies; especially in the presence of moderately elevated serum creatine kinase, predominant axial and humeroperoneal weakness, spine rigidity, and joint contractures.