The β-tropomyosin gene encodes a component of the sarcomeric thin filament. Rod-shaped dimers of tropomyosin regulate actin-myosin interactions and β-tropomyosin mutations have been associated with nemaline myopathy, cap myopathy, Escobar syndrome and distal arthrogryposis types 1A and 2B. In this study, we expand the allelic spectrum of β-tropomyosin-related myopathies through the identification of a novel β-tropomyosin mutation in two clinical contexts not previously associated with β-tropomyosin. The first clinical phenotype is core-rod myopathy, with a β-tropomyosin mutation uncovered by whole exome sequencing in a family with autosomal dominant distal myopathy and muscle biopsy features of both minicores and nemaline rods. The second phenotype, observed in four unrelated families, is autosomal dominant trismus-pseudocamptodactyly syndrome (distal arthrogryposis type 7; previously associated exclusively with myosin heavy chain 8 mutations). In all four families, the mutation identified was a novel 3-bp in-frame deletion (c.20_22del) that results in deletion of a conserved lysine at the seventh amino acid position (p.K7del). This is the first mutation identified in the extreme N-terminus of β-tropomyosin. To understand the potential pathogenic mechanism(s) underlying this mutation, we performed both computational analysis and in vivo modelling. Our theoretical model predicts that the mutation disrupts the N-terminus of the α-helices of dimeric β-tropomyosin, a change predicted to alter protein-protein binding between β-tropomyosin and other molecules and to disturb head-to-tail polymerization of β-tropomyosin dimers. To create an in vivo model, we expressed wild-type or p.K7del β-tropomyosin in the developing zebrafish. p.K7del β-tropomyosin fails to localize properly within the thin filament compartment and its expression alters sarcomere length, suggesting that the mutation interferes with head-to-tail β-tropomyosin polymerization and with overall sarcomeric structure. We describe a novel β-tropomyosin mutation, two clinical-histopathological phenotypes not previously associated with β-tropomyosin and pathogenic data from the first animal model of β-tropomyosin-related myopathies.

PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataracts) is a recently described autosomal-recessive neurodegenerative disease caused by mutations in the --hydrolase domain-containing 12 gene (ABHD12). Only five homozygous ABHD12 mutations have been reported and the pathogenesis of PHARC remains unclear. We evaluated a woman who manifested short stature as well as the typical features of PHARC. Sequence analysis of ABHD12 revealed a novel heterozygous c.1129A>T (p.Lys377*) mutation. Targeted comparative genomic hybridization detected a 59-kb deletion that encompasses exon 1 of ABHD12 and exons 1-4 of an adjacent gene, GINS1, and includes the promoters of both genes. The heterozygous deletion was also carried by the patient's asymptomatic mother. Quantitative reverse transcription-PCR demonstrated approximate to 50% decreased expression of ABHD12RNA in lymphoblastoid cell lines from both individuals. Activity-based protein profiling of serine hydrolases revealed absence of ABHD12 hydrolase activity in the patient and 50% reduction in her mother. This is the first report of compound heterozygosity in PHARC and the first study to describe how a mutation might affect ABHD12 expression and function. The possible involvement of haploinsufficiency for GINS1, a DNA replication complex protein, in the short stature of the patient and her mother requires further studies. (C) 2013 Wiley Periodicals, Inc.

Charcot Marie Tooth disease (CMT) encompasses the inherited peripheral neuropathies. While four genes have been found to cause over 90 % of genetically identifiable causes of CMT (PMP22, GJB1, MPZ, MFN2), at least 51 genes and loci have been found to cause CMT when mutated, creating difficulties for clinicians to find a genetic subtype for families. Here, the classic features of CMT as well as characteristic features of the most common subtypes of CMT are described, as well as methods for narrowing down the possible subtypes. Psychosocial concerns particular to the CMT population are identified. This is the most inclusive publication for CMT-specific genetic counseling.

Objective: Genetic study of a patient with progressive Polyneuropathy, Hearing loss, Ataxia, Retinitis pigmentosa, and Cataracts (PHARC). Background PHARC is a recently described autosomal recessive neurodegenerative disease caused by mutations in the anhydrolase domain containing 12 gene (ABHD12) that encodes an enzyme that catalyzes the hydrolysis of 2-arachidonoyl glycerol. Only four homozygous loss-of-function ABHD12 mutations have been reported to date. Design/Methods: We ascertained a 29-year-old woman of Northern European background who manifested the typical features of PHARC. Protein-coding exons of ABHD12 were sequenced in DNA from the patient and her unaffected mother and maternal half-brother. The ABHD12 deletion boundaries were determined by comparative genomic hybridization (CGH) on an array containing 106 oligonucleotide probes with ∼3 kb mean spacing. Quantitative PCR (qPCR) was performed on the patient9s lymphoblastoid line RNA. Results: The patient manifested congenital foot deformities requiring surgery, childhood-onset progressive hearing loss requiring cochlear implants, adolescent-onset cataracts with retinitis pigmentosa and macular edema, and a demyelinating motor/sensory peripheral neuropathy. Her brain MRI was normal. In addition, she and her unaffected mother both have short stature, 4911", whereas her unaffected maternal half-brother has normal height. Sequencing of ABHD12 in the patient identified a novel 1129a→t (Lys377X) mutation in exon 12. Targeted CGH detected a 59 kb deletion that encompassed exon 1 of ABHD12 and exons 1-4 of an adjacent gene, GINS1, and includes the promoters of both genes. The deletion was found in the mother but not in the maternal half-brother. RNA qPCR revealed remarkably decreased expression of ABHD12 in the patient. Conclusions: We report a fifth ABHD12 mutation and the first instance of compound heterozygosity in PHARC. The mutations severely reduce ABHD12 expression; effect on hydrolase activity is under investigation. The possible involvement of haploinsufficiency for GINS1, a DNA replication complex protein, in the short stature of the patient and her mother requires further study. Supported by: The Department of Veterans Affairs and R01 NS069719-01. Disclosure: Dr. Chen has received license fee payments from Athena Diagnostics. Dr. Davis has nothing to disclose. Dr. Mefford has nothing to disclose. Dr. Sul has nothing to disclose. Dr. Naydenov has nothing to disclose. Dr. Barloon has nothing to disclose. Dr. Wolff has nothing to disclose. Dr. Matsushita has nothing to disclose. Dr. Smith has nothing to disclose. Dr. Stella has nothing to disclose. Dr. Raskind has received (royalty or license fee or contractual rights) payments from Athena Diagnostics. Dr. Bird has received personal compensation for activities with Athena Diagnostics for speakers bureau and licensing fees.Dr. Bird has received liscensing payments from Athena Diagnostics.

Clinical neurology has benefitted greatly from recent remarkable advances in molecular genetics. In 1991, we could approximate a patient's risk for Huntington disease (HD) based only on linkage analysis. Now, 20 years later, not only can we identify the HD mutation with certainty, we can do the same with several hundred diseases. Whole genome or exome sequencing will soon allow for one-step interrogation of multiple genes for an even larger range of diseases. The recognition of these genes and their associated proteins in combination with new technology has led to creative new approaches to treatment. The challenge for the practicing neurologist is to provide clinically relevant and accurate interpretation of the genetic test results, with successfully treating once "incurable" neurogenetic diseases our ultimate goal.

Clinical neurology has benefitted greatly from recent remarkable advances in molecular genetics. In 1991, we could approximate a patient’s risk for Huntington disease (HD) based only on linkage analysis. Now, 20 years later, not only can we identify the HD mutation with certainty, we can do the same with several hundred diseases. Whole genome or exome sequencing will soon allow for one-step interrogation of multiple genes for an even larger range of diseases. The recognition of these genes and their associated proteins in combination with new technology has led to creative new approaches to treatment. The challenge for the practicing neurologist is to provide clinically relevant and accurate interpretation of the genetic test results, with successfully treating once “incurable” neurogenetic diseases our ultimate goal.

Background With the exception of Huntington disease, the psychological and psychosocial impact of DNA testing for neurogenetic disorders has not been well studied. Objective To evaluate the psychosocial impact of genetic testing for autosomal dominant forms of hereditary ataxia and neuromuscular disorders. Patients Fifty subjects at risk for autosomal dominant forms of spinocerebellar ataxia (n = 11), muscular dystrophy (n = 28), and hereditary neuropathy (n = 12). Design and Setting A prospective, descriptive, observational study in a university setting of individuals who underwent genetic counseling and DNA testing. Participants completed 3 questionnaires before testing and at regular intervals after testing. The questionnaire set included the Revised Impact of Event Scale, the Hospital Anxiety and Depression Scale, demographic information, and an assessment of attitudes and feelings about genetic testing. Results Thirty-nine subjects (78%) completed 6 months to 5 years of posttest follow-up. Common reasons for pursuing genetic testing were to provide an explanation for symptoms, emotional relief, and information for future planning. Thirty-four (68%) had positive and 16 (32%) had negative genetic results. In those with a positive result, 26 (76%) had nonspecific signs or symptoms of the relevant disorder. Forty-two participants (84%) felt genetic testing was beneficial. Groups with positive and negative test results coped well with results. However, 13 subjects (10 with positive and 3 with negative results) reported elevated anxiety levels, and 3 (1 with positive and 2 with negative results) expressed feelings of depression during the follow-up period. The test result was not predictive of anxiety or depression. Conclusions Most individuals find neurogenetic testing to be beneficial, regardless of the result. Anxiety or depression may persist in some persons with positive or negative test results. Testing can have a demonstrable impact on family planning and interpersonal relationships. Further studies are needed to assess the long-term impact of such testing.

BACKGROUND:DNA testing of persons at risk for hereditary, degenerative neurologic diseases is relatively new. Only anecdotal reports of such testing in familial Alzheimer disease (FAD) exist, and little is know about the personal and social impact of such testing.METHODS:In a descriptive, observational study, individuals at 50% risk for autosomal dominant, early-onset FAD or frontotemporal dementia with parkinsonism linked to chromosome 17 underwent DNA testing for the genetic mutations previously identified in affected family members. Individuals were followed up for (1/2) to 3 years and were interviewed regarding attitudes toward the testing process and the impact of the results.RESULTS:Twenty-one (8.4%) of 251 persons at risk for FAD or frontotemporal dementia requested genetic testing. The most common reasons for requesting testing were concern about early symptoms of dementia, financial or family planning, and relief from anxiety. Twelve individuals had positive DNA test results, and 6 of these had early symptoms of dementia; 8 had negative results; and 1 has not yet received results. Of 14 asymptomatic individuals completing testing, 13 believed the testing was beneficial. Two persons reported moderate anxiety and 1 reported moderate depression. As expected, persons with negative test results had happier experiences overall, but even they had to deal with ongoing anxiety and depression. Thus far, there have been no psychiatric hospitalizations, suicide attempts, or denials of insurance.CONCLUSIONS:Genetic testing in early-onset FAD and frontotemporal dementia can be completed successfully. Most individuals demonstrate effective coping skills and find the testing to be beneficial, but long-term effects remain unknown.