Lev G. Goldfarb

Missense mutations in desmin associated with familial cardiac and skeletal myopathy.

Desmin-related myopathy (OMIM 601419) is a familial disorder characterized by skeletal muscle weakness associated with cardiac conduction blocks, arrhythmias and restrictive heart failure, and by intracytoplasmic accumulation of desmin-reactive deposits in cardiac and skeletal muscle cells. The underlying molecular mechanisms are unknown. Involvement of the desmin gene (DES) has been excluded in three families diagnosed with desmin-related myopathy. We report two new families with desmin-related cardioskeletal myopathy associated with mutations in the highly conserved carboxy-terminal end of the desmin rod domain. A heterozygous A337P mutation was identified in a family with an adult-onset skeletal myopathy and mild cardiac involvement. Compound heterozygosity for two other mutations, A360P and N393I, was detected in a second family characterized by childhood-onset aggressive course of cardiac and skeletal myopathy.

Glycyl tRNA synthetase mutations in Charcot-Marie-Tooth disease type 2D and distal spinal muscular atrophy type V

Charcot-Marie-Tooth disease type 2D (CMT2D) and distal spinal muscular atrophy type V (dSMA-V) are axonal peripheral neuropathies inherited in an autosomal dominant fashion. Our previous genetic and physical mapping efforts localized the responsible gene(s) to a well-defined region on human chromosome 7p. Here, we report the identification of four disease-associated missense mutations in the glycyl tRNA synthetase gene in families with CMT2D and dSMA-V. This is the first example of an aminoacyl tRNA synthetase being implicated in a human genetic disease, which makes genes that encode these enzymes relevant candidates for other inherited neuropathies and motor neuron diseases.

Mutations in familial Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker's syndrome

A host protein encoded by the gene specifying the scrapie amyloid precursor affects pathogenesis of the transmissible spongiform encephalopathies: Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinkers syndrome (GSS), and kuru in man, and scrapie in animals. We found a mutation in this gene of two patients with CJD from one family and a second mutation in the same gene in three patients with GSS from another family. The mutation in two related familial CJD patients changed glutamine in position 200 tolysine. This mutation was absent in other individuals including unrelated patients with familial CJD, sporadic CJD, and GSS. The other mutation in three GSS patients changed proline in position 102 to leucine, the same mutation described recently in some GSS families. We did not find it in six unaffected relatives of the GSS patients or in other individuals including sporadic and familial CJD patients. A rare insertion described earlier in one CJD family was also absent in all tested individuals.

Tragedy in a heartbeat: malfunctioning desmin causes skeletal and cardiac muscle disease

Muscle fiber deterioration resulting in progressive skeletal muscle weakness, heart failure, and respiratory distress occurs in more than 20 inherited myopathies. As discussed in this Review, one of the newly identified myopathies is desminopathy, a disease caused by dysfunctional mutations in desmin, a type III intermediate filament protein, or alphaB-crystallin, a chaperone for desmin. The range of clinical manifestations in patients with desminopathy is wide and may overlap with those observed in individuals with other myopathies. Awareness of this disease needs to be heightened, diagnostic criteria reliably outlined, and molecular testing readily available; this would ensure prevention of sudden death from cardiac arrhythmias and other complications.

Iatrogenic Creutzfeldt‐Jakob disease: An example of the interplay between ancient genes and modern medicine

We tested DNA from 15 centrally infected cases of iatrogenic Creutzfeldt-Jakob disease (CJD) (dura mater or corneal homografts and stereotactic EEG electrodes), 11 peripherally infected cases (native human growth hormone or gonadotrophin), and 110 control individuals for the presence of mutations in the chromosome 20 amyloid gene. No patient or control had any of the known pathogenic point or insert mutations found in familial disease, but allelic homozygosity at polymorphic codon 129 was present in all but two (92%) of the 26 patients, compared with 54 (50%) of the 110 controls (p < 0.001). Pooled data from all identified and tested cases of iatrogenic disease yielded a worldwide total of 56 patients, of whom all but four were homozygous at codon 129 (p < 0.001). These findings support the thesis that homozygosity at codon 129 enhances susceptibility to iatrogenic infections of both central and peripheral origin, with evident implications for the population of dura mater homograft and pituitary hormone recipients whose lives have been complicated by the possibility of exposure to the infectious agent of CJD.

Increased Susceptibility to Kuru of Carriers of the PRNP 129 Methionine/Methionine Genotype

Kuru reached epidemic proportions by the mid-twentieth century among the Fore people of New Guinea and disappeared after the abolition of cannibalistic rituals. To determine susceptibility to kuru and its role in the spread and elimination of the epidemic, we analyzed the PRNP gene coding sequences in 5 kuru patients; no germline mutations were found. Analysis of the PRNP 129 methionine (M)/valine (V) polymorphism in 80 patients and 95 unaffected controls demonstrated that the kuru epidemic preferentially affected individuals with the M/M genotype. A higher representation of M/M carriers was observed among the affected young Fore males entering the age of risk, whereas a lower frequency of M/M homozygotes was found among the survivors. M/V and V/V genotypes predisposed to a lower risk of disease development and longer incubation times. These findings are relevant to the current outbreak of variant Creutzfeldt-Jakob disease (vCJD) in the United Kingdom, because all vCJD patients tested thus far have been M/M carriers.

Distinct muscle imaging patterns in myofibrillar myopathies

Objective: To compare muscle imaging findings in different subtypes of myofibrillar myopathies (MFM) in order to identify characteristic patterns of muscle alterations that may be helpful to separate these genetic heterogeneous muscular disorders. Methods: Muscle imaging and clinical findings of 46 patients with MFM were evaluated (19 desminopathy, 12 myotilinopathy, 11 filaminopathy, 1 αB-crystallinopathy, and 3 ZASPopathy). The data were collected retrospectively in 43 patients and prospectively in 3 patients. Results: In patients with desminopathy, the semitendinosus was at least equally affected as the biceps femoris, and the peroneal muscles were never less involved than the tibialis anterior (sensitivity of these imaging criteria to detect desminopathy in our cohort 100%, specificity 95%). In most of the patients with myotilinopathy, the adductor magnus showed more alterations than the gracilis muscle, and the sartorius was at least equally affected as the semitendinosus (sensitivity 90%, specificity 93%). In filaminopathy, the biceps femoris and semitendinosus were at least equally affected as the sartorius muscle, and the medial gastrocnemius was more affected than the lateral gastrocnemius. The semimembranosus mostly showed more alterations than the adductor magnus (sensitivity 88%, specificity 96%). Early adult onset and cardiac involvement was most often associated with desminopathy. In patients with filaminopathy, muscle weakness typically beginning in the 5th decade of life was mostly pronounced proximally, while late adult onset (>50 years) with distal weakness was more often present in myotilinopathy. Conclusions: Muscle imaging in combination with clinical data may be helpful for separation of distinct myofibrillar myopathy subtypes and in scheduling of genetic analysis.

Gluten sensitivity in sporadic and hereditary cerebellar ataxia

Gluten sensitivity, with or without classical celiac disease symptoms and intestinal pathology, has been suggested as a potentially treatable cause of sporadic cerebellar ataxia. Here, we investigated the prevalence of abnormally high serum immunoglobulin A (IgA) and IgG anti‐gliadin antibody titers and typical human lymphocyte antigen (HLA) genotypes in 50 patients presenting with cerebellar ataxia who were tested for molecularly characterized hereditary ataxias. A high prevalence of gluten sensitivity was found in patients with sporadic (7/26; 27%) and autosomal dominant (9/24; 37%) ataxias, including patients with known ataxia genotypes indicating a hitherto unrecognized association between hereditary ataxias and gluten sensitivity. Further studies are needed to determine whether gluten sensitivity contributes to cerebellar degeneration in patients with hereditary cerebellar ataxia. Patients with hereditary ataxia (including asymptomatic patients with known ataxia genotype) should be considered for screening for gluten sensitivity and gluten‐free diet trials. Ann Neurol 2001;49:540–543

Screening of the entire ryanodine receptor type 1 coding region for sequence variants associated with Malignant hyperthermia susceptibility in the North American Population

Background:Malignant hyperthermia (MH) is a life-threatening and frequently fatal disorder triggered by commonly used anesthetics. MH susceptibility is a genetically determined predisposition to the development of MH. Mutations in the ryanodine receptor type 1 (RYR1) gene are the major cause of MH susceptibility. The authors sought to develop a reliable genetic screening strategy based on efficient and relatively inexpensive mutation-detection procedures. Methods:A cohort (n = 30) of North American MH patients and MH-susceptible individuals was studied. RNA and DNA extracted from muscle tissue or blood lymphocytes were used for analysis. The entire RYR1 coding region was amplified in 57 overlapping fragments and subjected to denaturing high-performance liquid chromatography analysis followed by direct nucleotide sequencing to characterize RYR1 alterations. Results:Nine previously reported and nine unknown RYR1 mutations were identified in 21 of 30 studied patients (70%). Some of the new mutations were located outside of known mutational “hot spots,” suggesting that RYR1 contains previously unknown mutation-prone areas requiring analysis. The North American MH/MH-susceptible population is characterized by a high RYR1 allelic heterogeneity. Conclusions:Denaturing high-performance liquid chromatography analysis of RNA samples extracted from the biopsied skeletal muscle followed by DNA sequencing is a highly efficient methodology for RYR1 mutation detection. This approach allows increasing the rate of mutation detection to 70% and identifying mutations in the entire RYR1 coding region.

Dominant Mutations in KBTBD13, a Member of the BTB/Kelch Family, Cause Nemaline Myopathy with Cores

We identified a member of the BTB/Kelch protein family that is mutated in nemaline myopathy type 6 (NEM6), an autosomal-dominant neuromuscular disorder characterized by the presence of nemaline rods and core lesions in the skeletal myofibers. Analysis of affected families allowed narrowing of the candidate region on chromosome 15q22.31, and mutation screening led to the identification of a previously uncharacterized gene, KBTBD13, coding for a hypothetical protein and containing missense mutations that perfectly cosegregate with nemaline myopathy in the studied families. KBTBD13 contains a BTB/POZ domain and five Kelch repeats and is expressed primarily in skeletal and cardiac muscle. The identified disease-associated mutations, C.742C>A (p.Arg248Ser), c.1170G>C (p.Lys390Asn), and c.1222C>T (p.Arg408Cys), located in conserved domains of Kelch repeats, are predicted to disrupt the molecules beta-propeller blades. Previously identified BTB/POZ/Kelch-domain-containing proteins have been implicated in a broad variety of biological processes, including cytoskeleton modulation, regulation of gene transcription, ubiquitination, and myofibril assembly. The functional role of KBTBD13 in skeletal muscle and the pathogenesis of NEM6 are subjects for further studies.