Gudrun Schreiber

Desmin-related myopathy with Mallory body-like inclusions is caused by mutations of the selenoprotein N gene.

Desmin‐related myopathies (DRMs) are a heterogeneous group of muscle disorders, morphologically defined by intrasarcoplasmic aggregates of desmin. Mutations in the desmin and the α‐B crystallin genes account for approximately one third of the DRM cases. The genetic basis of the other forms remain unknown, including the early‐onset, recessive form with Mallory body–like inclusions (MB‐DRMs), first described in five related German patients. Recently, we identified the selenoprotein N gene (SEPN1) as responsible for SEPN‐related myopathy (SEPN‐RM), a unique early‐onset myopathy formerly divided in two different nosological categories: rigid spine muscular dystrophy and the severe form of classical multiminicore disease. The finding of Mallory body–like inclusions in two cases of genetically documented SEPN‐RM led us to suspect a relationship between MB‐DRM and SEPN1. In the original MB‐DRM German family, we demonstrated a linkage of the disease to the SEPN1 locus (1p36), and subsequently a homozygous SEPN1 deletion (del 92 nucleotide −19/+73) in the affected patients. A comparative reevaluation showed that MB‐DRM and SEPN‐RM share identical clinical features. Therefore, we propose that MB‐DRM should be categorized as SEPN‐RM. These findings substantiate the molecular heterogeneity of DRM, expand the morphological spectrum of SEPN‐RM, and implicate a necessary reassessment of the nosological boundaries in early‐onset myopathies. Ann Neurol 2004

Mutations in FKBP14 cause a variant of Ehlers-Danlos syndrome with progressive kyphoscoliosis, myopathy, and hearing loss.

We report on an autosomal-recessive variant of Ehlers-Danlos syndrome (EDS) characterized by severe muscle hypotonia at birth, progressive scoliosis, joint hypermobility, hyperelastic skin, myopathy, sensorineural hearing impairment, and normal pyridinoline excretion in urine. Clinically, the disorder shares many features with the kyphoscoliotic type of EDS (EDS VIA) and Ullrich congenital muscular dystrophy. Linkage analysis in a large Tyrolean kindred identified a homozygous frameshift mutation in FKBP14 in two affected individuals. Based on the cardinal clinical characteristics of the disorder, four additional individuals originating from different European countries were identified who carried either homozygous or compound heterozygous mutations in FKBP14. FKBP14 belongs to the family of FK506-binding peptidyl-prolyl cis-trans isomerases (PPIases). ER-resident FKBPs have been suggested to act as folding catalysts by accelerating cis-trans isomerization of peptidyl-prolyl bonds and to act occasionally also as chaperones. We demonstrate that FKBP14 is localized in the endoplasmic reticulum (ER) and that deficiency of FKBP14 leads to enlarged ER cisterns in dermal fibroblasts in vivo. Furthermore, indirect immunofluorescence of FKBP14-deficient fibroblasts indicated an altered assembly of the extracellular matrix in vitro. These findings suggest that a disturbance of protein folding in the ER affecting one or more components of the extracellular matrix might cause the generalized connective tissue involvement in this disorder. FKBP14 mutation analysis should be considered in all individuals with apparent kyphoscoliotic type of EDS and normal urinary pyridinoline excretion, in particular in conjunction with sensorineural hearing impairment.

Ullrich congenital muscular dystrophy: connective tissue abnormalities in the skin support overlap with Ehlers-Danlos syndromes.

Ullrich congenital muscular dystrophy (UCMD) is caused by mutations in the three genes coding for the alpha chains of collagen VI and characterized by generalized muscle weakness, striking hypermobility of distal joints in conjunction with variable contractures of more proximal joints, and normal intellectual development. The diagnosis is supported by abnormal immunoreactivity for collagen VI on muscle biopsies. As patients with UCMD show clinical characteristics typical of classical disorders of connective tissue such as Ehlers–Danlos syndromes (EDS), we investigated the ultrastructure of skin biopsy samples from patients with UCMD (n=5). Electron microscopy of skin biopsies revealed ultrastructural abnormalities in all cases, including alterations of collagen fibril morphology (variation in size and composite fibers) and increase in ground substance, which resemble those seen in patients with EDS. Our findings suggest that there is a true connective tissue component as part of the phenotypic spectrum of UCMD and that there is considerable clinical as well as morphological overlap between UCMD and classic connective tissue disorders.

Exon skipping mutations in collagen VI are common and are predictive for severity and inheritance

Mutations in the genes encoding collagen VI (COL6A1, COL6A2, and COL6A3) cause Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD), two related conditions of differing severity. BM is a relatively mild dominantly inherited disorder characterized by proximal weakness and distal joint contractures. UCMD was originally regarded as an exclusively autosomal recessive condition causing severe muscle weakness with proximal joint contractures and distal hyperlaxity. We and others have subsequently modified this model when we described UCMD patients with heterozygous in‐frame deletions acting in a dominant‐negative way. Here we report 10 unrelated patients with a UCMD clinical phenotype and de novo dominant negative heterozygous splice mutations in COL6A1, COL6A2, and COL6A3 and contrast our findings with four UCMD patients with recessively acting splice mutations and two BM patients with heterozygous splice mutations. We find that the location of the skipped exon relative to the molecular structure of the collagen chain strongly correlates with the clinical phenotype. Analysis by immunohistochemical staining of muscle biopsies and dermal fibroblast cultures, as well as immunoprecipitation to study protein biosynthesis and assembly, suggests different mechanisms each for exon skipping mutations underlying dominant UCMD, dominant BM, and recessive UCMD. We provide further evidence that de novo dominant mutations in severe UCMD occur relatively frequently in all three collagen VI chains and offer biochemical insight into genotype–phenotype correlations within the collagen VI–related disorders by showing that severity of the phenotype depends on the ability of mutant chains to be incorporated in the multimeric structure of collagen VI. Hum Mutat 29(6), 809–822, 2008.

Long-term follow-up in patients with congenital myasthenic syndrome due to CHAT mutations.

BACKGROUND Congenital myasthenic syndromes (CMSs) are a group of clinically and genetically heterogeneous inherited disorders of the neuromuscular junction. Mutations in the acetylcholine transferase (CHAT) gene cause a pre-synaptic CMS, typically associated with episodic apnoea and worsening of myasthenic symptoms during crises caused by infections, fever or stress. Between crises symptoms may be mild and variable. Acetylcholinesterase - inhibitor therapy is reported to improve clinical symptoms and reduce crises. PATIENTS AND METHODS We present data on the long-term follow-up of 11 patients with a congenital myasthenic syndrome due to nine different CHAT mutations; ten of the patients have not been previously reported. RESULTS AND CONCLUSIONS Manifestation varied from the neonatal period to the age of two years, follow-up time from nine months to 12 years. This cohort of CHAT patients studied here enabled us to describe two distinct phenotypes: The neonatal-onset group suffers from apnoeic crises, respirator dependency and bulbar weakness. Apnoea should be carefully distinguished from seizures; a CMS should be taken into account early to start appropriate therapy. Infantile-onset patients show mild permanent weakness, but experience apnoeic crises and worsening which resolve with Acetylcholinesterase - inhibitor treatment. However, after several years of treatment proximal muscle strength may decrease and lead to wheelchair dependency despite the continuation of Acetylcholinesterase - inhibitor therapy.

Sensitivity and specificity of qualitative muscle ultrasound in assessment of suspected neuromuscular disease in childhood

Muscle ultrasound is considered a useful noninvasive technique for visualizing normal and pathological skeletal muscle. We determined the accuracy of qualitative muscle ultrasound in the discrimination of normal muscle from myopathic, neurogenic, and unspecifically abnormal tissue changes in the evaluation of suspected NMD in childhood. Sensitivity and specificity of muscle ultrasound were assessed by comparing sonographic classification of muscle tissue changes in 134 children with definitive diagnosis as provided by muscle histology or mutation analysis performed subsequently to the sonography. We found a sensitivity of 81% and a specificity of 96% for detection of any abnormal muscle tissue alteration by ultrasound. For detection of neurogenic changes, sensitivity was 77% with even higher specificity (98%). Accuracy was slightly lower for myopathic changes (79%) and clearly lower for unspecific abnormal tissue alterations (70%). Accuracy of ultrasound was lower in younger children. High reliability of muscle sonography justifies a more widespread use of this method in evaluation of suspected NMD in childhood.

Recessive and dominant mutations in COL12A1 cause a novel EDS/myopathy overlap syndrome in humans and mice

Collagen VI-related myopathies are disorders of connective tissue presenting with an overlap phenotype combining clinical involvement from the muscle and from the connective tissue. Not all patients displaying related overlap phenotypes between muscle and connective tissue have mutations in collagen VI. Here, we report a homozygous recessive loss of function mutation and a de novo dominant mutation in collagen XII (COL12A1) as underlying a novel overlap syndrome involving muscle and connective tissue. Two siblings homozygous for a loss of function mutation showed widespread joint hyperlaxity combined with weakness precluding independent ambulation, while the patient with the de novo missense mutation was more mildly affected, showing improvement including the acquisition of walking. A mouse model with inactivation of the Col12a1 gene showed decreased grip strength, a delay in fiber-type transition and a deficiency in passive force generation while the muscle seems more resistant to eccentric contraction induced force drop, indicating a role for a matrix-based passive force-transducing elastic element in the generation of the weakness. This new muscle connective tissue overlap syndrome expands on the emerging importance of the muscle extracellular matrix in the pathogenesis of muscle disease.

Quantitative proton MRS of cerebral metabolites in laminin α2 chain deficiency

Congenital muscular dystrophy (CMD) due to merosin (laminin a2 chain) deficiency is an autosomal recessively inherited disorder characterized by severe muscular weakness and hypotonia from birth on. Brain involvement is the rule and characterized by variable T2 hyperintensities of white matter which appears swollen on cranial MRI. The pathophysiology of these white matter changes is not clear. In five patients with laminin a2 deficient CMD we performed short-echo time localized proton MRS with determination of absolute metabolite concentrations in grey and white matter. In affected white matter, a consistent pattern of metabolites was detected comprising reduced concentrations of N-acetylaspartate and N-acetylaspartylglutamate, creatine, and phosphocreatine, and to a milder degree of choline-containing compounds. In contrast, concentrations of myo-inositol were in the normal range. Spectra of cortical and subcortical grey matter were normal. The observed metabolite profile is consistent with white matter edema, that is reduced cellular density, and relative astrocytosis. This interpretation is in line with the hypothesis that laminin a2 deficiency results in leakage of fluids across the blood–brain barrier and a histopathological report of astrocytic proliferation in CMD.

A cohort of 17 patients with kyphoscoliotic Ehlers-Danlos syndrome caused by biallelic mutations in FKBP14: expansion of the clinical and mutational spectrum and description of the natural history.

PurposeIn 2012 we reported in six individuals a clinical condition almost indistinguishable from PLOD1-kyphoscoliotic Ehlers–Danlos syndrome (PLOD1-kEDS), caused by biallelic mutations in FKBP14, and characterized by progressive kyphoscoliosis, myopathy, and hearing loss in addition to connective tissue abnormalities such as joint hypermobility and hyperelastic skin. FKBP14 is an ER-resident protein belonging to the family of FK506-binding peptidyl-prolyl cis–trans isomerases (PPIases); it catalyzes the folding of type III collagen and interacts with type III, type VI, and type X collagens. Only nine affected individuals have been reported to date.MethodsWe report on a cohort of 17 individuals with FKBP14-kEDS and the follow-up of three previously reported patients, and provide an extensive overview of the disorder and its natural history based on clinical, biochemical, and molecular genetics data.ResultsBased on the frequency of the clinical features of 23 patients from the present and previous cohorts, we define major and minor features of FKBP14-kEDS. We show that myopathy is confirmed by histology and muscle imaging only in some patients, and that hearing impairment is predominantly sensorineural and may not be present in all individuals.ConclusionOur data further support the extensive clinical overlap with PLOD1-kEDS and show that vascular complications are rare manifestations of FKBP14-kEDS.