Mutations in embryonic myosin heavy chain (MYH3) cause Freeman-Sheldon syndrome and Sheldon-Hall syndrome

Freeman-Sheldon syndrome--prenatal and postnatal diagnosis

A six-day-old girl, born to normal non-consanguineous parents presented with mask like facies with a small mouth giving a 'whistling' appearance. Other dysmorphic features include deep set eyes, broad nasal bridge, long philtrum and 'H' shaped cutaneous dimple on the chin. There was congenital windmill vane hand position and severe talipes equinovarus deformity. The above features are characteristic of Freeman-Sheldon syndrome also known as Whistling Face syndrome. Ultrasound scanning during 8(th) month of the pregnancy showed the fetus to have facial abnormality and bilateral clenched hand and talipes with extension contractures of knees. Provisional diagnosis of FSS was made which was confirmed after the birth. Thus all cases of Arthrogryposis during prenatal scan should be carefully looked for the facial abnormality in the fetus.

Myosin binding protein C1: a novel gene for autosomal dominant distal arthrogryposis type 1

Distal arthrogryposis type I (DA1) is a disorder characterized by congenital contractures of the hands and feet for which few genes have been identified. Here we describe a five-generation family with DA1 segregating as an autosomal dominant disorder with complete penetrance. Genome-wide linkage analysis using Affymetrix GeneChip Mapping 10K data from 12 affected members of this family revealed a multipoint LOD(max) of 3.27 on chromosome 12q. Sequencing of the slow-twitch skeletal muscle myosin binding protein C1 (MYBPC1), located within the linkage interval, revealed a missense mutation (c.706T>C) that segregated with disease in this family and causes a W236R amino acid substitution. A second MYBPC1 missense mutation was identified (c.2566T>C)(Y856H) in another family with DA1, accounting for an MYBPC1 mutation frequency of 13% (two of 15). Skeletal muscle biopsies from affected patients showed type I (slow-twitch) fibers were smaller than type II fibers. Expression of a green fluorescent protein (GFP)-tagged MYBPC1 construct containing WT and DA1 mutations in mouse skeletal muscle revealed robust sarcomeric localization. In contrast, a more diffuse localization was seen when non-fused GFP and MYBPC1 proteins containing corresponding MYBPC3 amino acid substitutions (R326Q, E334K) that cause hypertrophic cardiomyopathy were expressed. These findings reveal that the MYBPC1 is a novel gene responsible for DA1, though the mechanism of disease may differ from how some cardiac MYBPC3 mutations cause hypertrophic cardiomyopathy.

Evaluation of embryonic and perinatal myosin gene mutations and the etiology of congenital idiopathic clubfoot

BACKGROUND

Congenital idiopathic clubfoot is the most common musculoskeletal birth defect that develops during the fetal period, but with no known etiology. MYH 2, 3, 7, and 8 are expressed embryonically or perinatally, the period during which congenital idiopathic clubfoot develops; are all components of Type II muscle, which is consistently decreased in clubfoot patients; and are associated with several muscle contracture syndromes that have associated clubfoot deformities. In this study, we hypothesized that a mutation in an embryonic or perinatal myosin gene could be associated with congenital idiopathic clubfoot.

METHODS

We screened the exons, splice sites, and predicted promoters of 24 bilateral congenital idiopathic clubfoot patients and 24 matched controls in MYH 1, 2, 3, and 8 via sequence-based analysis, and screened an additional 76 patients in each discovered SNP.

RESULTS

Although many single-nucleotide polymorphisms were found; none proved to be significantly associated with the phenotype of congenital idiopathic clubfoot. Also, no known mutations that cause distal arthrogryposis syndromes were found in the congenital idiopathic clubfoot patients.

CONCLUSIONS

These findings demonstrate that congenital idiopathic clubfoot has a different pathophysiology than the clubfoot seen in distal arthrogryposis syndromes, and defects in myosin are most likely not directly responsible for the development of congenital clubfoot. Given the complexity of early myogenesis, many regulatory candidate genes remain that could cause defects in the hypaxial musculature that is invariably observed in congenital idiopathic clubfoot.

CLINICAL RELEVANCE

This study further differentiates congenital idiopathic clubfoot as distinct from other complex genetic syndromes that can present with similar deformities, and thus facilitates further research to improve the clinical diagnosis and treatment of congenital idiopathic clubfoot.

Functional diversity among a family of human skeletal muscle myosin motors

Human skeletal muscle fibers express five highly conserved type-II myosin heavy chain (MyHC) genes in distinct spatial and temporal patterns. In addition, the human genome contains an intact sixth gene, MyHC-IIb, which is thought under most circumstances not to be expressed. The physiological and biochemical properties of individual muscle fibers correlate with the predominantly expressed MyHC isoform, but a functional analysis of homogenous skeletal muscle myosin isoforms has not been possible. This is due to the difficulties of separating the multiple isoforms usually coexpressed in muscle fibers, as well as the lack of an expression system that produces active recombinant type II skeletal muscle myosin. In this study we describe a mammalian muscle cell expression system and the functional analysis of all six recombinant human type II skeletal muscle myosin isoforms. The diverse biochemical activities and actin-filament velocities of these myosins indicate that they likely have distinct functions in muscle. Our data also show that ATPase activity and motility are generally correlated for human skeletal muscle myosins. The exception, MyHC-IIb, encodes a protein that is high in ATPase activity but slow in motility; this is the first functional analysis of the protein from this gene. In addition, the developmental isoforms, hypothesized to have low ATPase activity, were indistinguishable from adult-fast MyHC-IIa and the specialized MyHC-Extraocular isoform, that was predicted to be the fastest of all six isoforms but was functionally similar to the slower isoforms.

Exome sequencing identifies the cause of a mendelian disorder

We demonstrate the first successful application of exome sequencing to discover the gene for a rare, Mendelian disorder of unknown cause, Miller syndrome (OMIM %263750). For four affected individuals in three independent kindreds, we captured and sequenced coding regions to a mean coverage of 40X, and sufficient depth to call variants at ~97% of each targeted exome. Filtering against public SNP databases and a small number of HapMap exomes for genes with two novel variants in each of the four cases identified a single candidate gene, DHODH, which encodes a key enzyme in the pyrimidine de novo biosynthesis pathway. Sanger sequencing confirmed the presence of DHODH mutations in three additional families with Miller syndrome. Exome sequencing of a small number of unrelated, affected individuals is a powerful, efficient strategy for identifying the genes underlying rare Mendelian disorders and will likely transform the genetic analysis of monogenic traits.

Skeletal muscle contractile gene (TNNT3, MYH3, TPM2) mutations not found in vertical talus or clubfoot

Arthrogryposis presents with lower limb contractures that resemble clubfoot and/or vertical talus. Recently, mutations in skeletal muscle contractile genes MYH3 (myosin heavy chain 3), TNNT3 (troponin T3), and TPM2 (tropomyosin 2) were identified in patients with distal arthrogryposis DA2A (Freeman-Sheldon syndrome) or DA2B (Sheldon-Hall syndrome). We asked whether the contractile genes responsible for distal arthrogryposis are also responsible for cases of familial clubfoot or vertical talus. We determined the frequency of MYH3, TNNT3, and TPM2 mutations in patients with idiopathic clubfoot, vertical talus, and distal arthrogryposis type 1 (DA1). We resequenced the coding exons of the MYH3, TNNT3, and TPM2 genes in 31 patients (five with familial vertical talus, 20 with familial clubfoot, and six with DA1). Variants were evaluated for segregation with disease in additional family members, and the frequency of identified variants was determined in a control population. In one individual with DA1, we identified a de novo TNNT3 mutation (R63H) previously identified in an individual with DA2B. No other causative mutations were identified, though we found several previously undescribed single-nucleotide polymorphisms of unknown importance. Although mutations in MYH3, TNNT3, and TPM2 are frequently associated with distal arthrogryposis syndromes, they were not present in patients with familial vertical talus or clubfoot. The TNNT3 R63H recurrent mutation identified in two unrelated individuals may be associated with either DA1 or DA2B.

LEVEL OF EVIDENCE

Level II, prospective study. See the Guidelines for Authors for a complete description of levels of evidence.

Update on clubfoot: etiology and treatment

Although clubfoot is one of the most common congenital abnormalities affecting the lower limb, it remains a challenge not only to understand its genetic origins but also to provide effective long-term treatment. This review provides an update on the etiology of clubfoot as well as current treatment strategies. Understanding the exact genetic etiology of clubfoot may eventually be helpful in determining both prognosis and the selection of appropriate treatment methods in individual patients. The primary treatment goal is to provide long-term correction with a foot that is fully functional and pain-free. To achieve this, a combination of approaches that applies the strengths of several methods (Ponseti method and French method) may be needed. Avoidance of extensive soft-tissue release operations in the primary treatment should be a priority, and the use of surgery for clubfoot correction should be limited to an "a la carte" mode and only after failed conservative methods.

LEVEL OF EVIDENCE

Level V, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Juvenile macular dystrophy and forearm pronation-supination restriction presenting with features of distal arthrogryposis type 5

The distal arthrogryposes are a heterogeneous group of conditions characterized by congenital contractures of hands and feet, and autosomal dominant inheritance. The concurrence of ophthalmoplegia and additional ocular findings distinguish distal arthrogryposis type 5 (DA5). This rare subtype has been described in 33 patients to date and its clinical spectrum of physical findings is still poorly understood. We report on a family with three individuals with DA5. The index case came to our attention because of restricted forearm pronation-supination and juvenile macular dystrophy. Further examination revealed short stature, firm muscles, stiff spine with lumbar hyperlordosis, generalized mild limitation of the large joints, external rotation of the hips, unilateral ptosis, exophoria, and abnormal photopic and scotopic responses on electroretinogram testing. However, there was no overt evidence of contractures of the distal joints. Examination of other affected family members revealed restricted range of movement of the small joints together with ulnar deviation of the fingers, and clarified the diagnosis. Our observations suggest that DA5 may have a very mild musculoskeletal phenotype and it should be considered in the differential of congenital contracture syndromes even in the absence of obvious distal joint involvement. Our observations also suggest that fundoscopy and ocular electrophysiological studies might be helpful in the evaluation of patients with otherwise unclassified distal arthrogryposes.

Sheldon-Hall syndrome

Sheldon-Hall syndrome (SHS) is a rare multiple congenital contracture syndrome characterized by contractures of the distal joints of the limbs, triangular face, downslanting palpebral fissures, small mouth, and high arched palate. Epidemiological data for the prevalence of SHS are not available, but less than 100 cases have been reported in the literature. Other common clinical features of SHS include prominent nasolabial folds, high arched palate, attached earlobes, mild cervical webbing, short stature, severe camptodactyly, ulnar deviation, and vertical talus and/or talipes equinovarus. Typically, the contractures are most severe at birth and non-progressive. SHS is inherited in an autosomal dominant pattern but about half the cases are sporadic. Mutations in either MYH3, TNNI2, or TNNT3 have been found in about 50% of cases. These genes encode proteins of the contractile apparatus of fast twitch skeletal muscle fibers. The diagnosis of SHS is based on clinical criteria. Mutation analysis is useful to distinguish SHS from arthrogryposis syndromes with similar features (e.g. distal arthrogryposis 1 and Freeman-Sheldon syndrome). Prenatal diagnosis by ultrasonography is feasible at 18–24 weeks of gestation. If the family history is positive and the mutation is known in the family, prenatal molecular genetic diagnosis is possible. There is no specific therapy for SHS. However, patients benefit from early intervention with occupational and physical therapy, serial casting, and/or surgery. Life expectancy and cognitive abilities are normal.

Congenital myopathies

PURPOSE OF REVIEW

The present review aims to discuss the pathological and clinical heterogeneity of congenital myopathies, and the overlap between the different variants highlighted by recent studies.

RECENT FINDINGS

The spectrum of pathological changes associated with known gene defects has widened, and new genes responsible for rare structural defects have been identified. The complexity of the classification of these conditions is highlighted by the realization that defects in the same gene can result in diverse phenotypes, including disorders traditionally classified as congenital myopathies with structural abnormalities, adult-onset disorders, conditions characterized by distal weakness and wasting, or distal arthrogryposis. There is a wider appreciation of the complexities of inheritance and of the value of noninvasive assessment, such as muscle MRI. New animal models provide a better understanding of pathogenesis and are highlighting therapeutic possibilities.

SUMMARY

The overlap of clinical and pathological features in the congenital myopathies has led to the recognition that diverse disorders are often associated with the same causative gene, and is challenging traditional classifications. Identification of further causative genes and development of new models will further the understanding of pathogenesis and development of therapies.

Freeman-Sheldon syndrome. A case report and review of the literature

The Authors describe a case of Freeman-Sheldon Syndrome, a rare congenital autosomal dominant disorder (gene mapped on chromosome 11p15.5) characterized by microstomia with crinkled lips, camptodactyly with ulnar deviation of the fingers and equinus-varus-supine clubfoot. The autosomal recessive form, even rarer and difficult to recognize, has a more severe clinical manifestation. The symptomatology is worsened by breathing and swallowing disorders due to the small orifices of the mouth and nose, which sometimes require tracheotomy to avoid obstruction of the airways.

Thick and thin filament gene mutations in striated muscle diseases

The sarcomere is the fundamental unit of cardiac and skeletal muscle contraction. During the last ten years, there has been growing awareness of the etiology of skeletal and cardiac muscle diseases originating in the sarcomere, an important evolving field. Many sarcomeric diseases affect newborn children, i. e. are congenital myopathies. The discovery and characterization of several myopathies caused by mutations in myosin heavy chain genes, coding for the major component of skeletal muscle thick filaments, has led to the introduction of a new entity in the field of neuromuscular disorders: myosin myopathies. Recently, mutations in genes coding for skeletal muscle thin filaments, associated with various clinical features, have been identified. These mutations evoke distinct structural changes within the sarcomeric thin filament. Current knowledge regarding contractile protein dysfunction as it relates to disease pathogenesis has failed to decipher the mechanistic links between mutations identified in sarcomeric proteins and skeletal myopathies, which will no doubt require an integrated physiological approach. The discovery of additional genes associated with myopathies and the elucidation of the molecular mechanisms of pathogenesis will lead to improved and more accurate diagnosis, including prenatally, and to enhanced potential for prognosis, genetic counseling and developing possible treatments for these diseases. The goal of this review is to present recent progress in the identification of gene mutations from each of the major structural components of the sarcomere, the thick and thin filaments, related to skeletal muscle disease. The genetics and clinical manifestations of these disorders will be discussed.

Impact of congenital talipes equinovarus etiology on treatment outcomes

Although congenital talipes equinovarus (CTEV) is often idiopathic, additional birth defects occur in some patients that may have an impact on the treatment of this disorder. The purpose of this study was to determine the prevalence of associated malformations, chromosomal abnormalities, or known genetic syndromes, and to compare treatment outcomes of children with idiopathic CTEV with children with non-idiopathic CTEV. Of 357 children evaluated, 273 (76%) had idiopathic CTEV (179 males, 94 females; mean age 2 y 1 mo [SD 1 y 2 mo], range 0-18 y) and 84 (24%) had non-idiopathic CETV (51 males, 33 females; mean age 2 y 5 mo [SD 2 y], range 0-16 y). Disorders affecting the nervous system were found in 46 (54%) children with non-idiopathic CTEV. In a subgroup of patients treated entirely at our institution (n=196), children with non-idiopathic CTEV (n=47) required more casts for correction than those with idiopathic CTEV (n=149; 5.3 vs 4.6; p=0.016). There was also a greater risk of recurrence in non-idiopathic CTEV (14.9% vs 4%; p=0.009), but no significant difference in the need for extensive surgery (2.7% vs 8.5%; p=0.096). Treatment was initiated at a mean age of 13 weeks (range 1 wk to 2 y 6 mo) for both idiopathic and non-idiopathic patients, and treatment was assessed during a minimum 2-year follow-up. Non-idiopathic CTEV can be successfully treated with the Ponseti method of serial casting, with low recurrence rates or need for surgery.

Phenotypic variation in trismus-pseudocamptodactyly syndrome caused by a recurrent MYH8 mutation

We report a 20-year-old man with trismus-pseudocamptodactyly (TPS) syndrome who was found to have the same MYH8 mutation, p.R674Q, described in previous families with TPS syndrome and in one family with a Carney complex variant, trismus and pseudocamptodactyly. This patient had facial asymmetry, ptosis and downslanting palpebral fissures and multiple joint involvement, with bilateral hip dysplasia, reduced elbow supination, vertical tali and talipes in addition to the classical findings of trismus and pseudocamptodactyly. These findings broaden the phenotype associated with p.R674Q mutations and support the use of MYH8 testing in patients with a clinical diagnosis of TPS syndrome.

Noncompaction of the ventricular myocardium is associated with a de novo mutation in the beta-myosin heavy chain gene

Noncompaction of the ventricular myocardium (NVM) is the morphological hallmark of a rare familial or sporadic unclassified heart disease of heterogeneous origin. NVM results presumably from a congenital developmental error and has been traced back to single point mutations in various genes. The objective of this study was to determine the underlying genetic defect in a large German family suffering from NVM. Twenty four family members were clinically assessed using advanced imaging techniques. For molecular characterization, a genome-wide linkage analysis was undertaken and the disease locus was mapped to chromosome 14ptel-14q12. Subsequently, two genes of the disease interval, MYH6 and MYH7 (encoding the α- and β-myosin heavy chain, respectively) were sequenced, leading to the identification of a previously unknown de novo missense mutation, c.842G>C, in the gene MYH7. The mutation affects a highly conserved amino acid in the myosin subfragment-1 (R281T). In silico simulations suggest that the mutation R281T prevents the formation of a salt bridge between residues R281 and D325, thereby destabilizing the myosin head. The mutation was exclusively present in morphologically affected family members. A few members of the family displayed NVM in combination with other heart defects, such as dislocation of the tricuspid valve (Ebstein's anomaly, EA) and atrial septal defect (ASD). A high degree of clinical variability was observed, ranging from the absence of symptoms in childhood to cardiac death in the third decade of life. The data presented in this report provide first evidence that a mutation in a sarcomeric protein can cause noncompaction of the ventricular myocardium.

Pulmonary disease is a component of distal arthrogryposis type 5

We report on a three-generation family with distal arthrogryposis type 5 (DA5). The family has four affected members in three generations with an apparent autosomal dominant pattern of inheritance. Three affected individuals were examined. All have distal joint contractures with absent flexion creases, limited mobility of all small and large joints, unusual stance with shortened heel cords and pes cavus, firm muscles, short stature, decreased extraocular movements, and pectus excavatum. The propositus has pulmonary hypertension secondary to chronic hypoxia from restrictive chest disease, alveolar hypoventilation, and residence at 7,000 feet above sea level. Cardiac catheterization documented pulmonary artery pressure of 54 mmHg and a pulmonary capillary wedge pressure of 10 mmHg. Pulmonary function tests showed severe chest restriction (forced vital capacity 30% of predicted; total lung capacity 51% predicted); and reduction of maximal inspiratory and expiratory pressures. Arterial blood gases documented alveolar hypoventilation. Restrictive chest disease is a component of DA5. This implies involvement of the skeletal, and/or respiratory muscles. All individuals diagnosed with DA5 should be evaluated for chest disease, alveolar hypoventilation, as treatment of chronic hypoxia may delay or reverse pulmonary hypertension.

An MYH9 human disease model in flies: site-directed mutagenesis of the Drosophila non-muscle myosin II results in hypomorphic alleles with dominant character

We investigated whether or not human disease-causing, amino acid substitutions in MYH9 could cause dominant phenotypes when introduced into the sole non-muscle myosin II heavy chain in Drosophila melanogaster (zip/MyoII). We characterized in vivo the effects of four MYH9-like mutations in the myosin rod-R1171C, D1430N, D1847K and R1939X-which occur at highly conserved residues. These engineered mutant heavy chains resulted in D. melanogaster non-muscle myosin II with partial wild-type function. In a wild-type genetic background, mutant heavy chains were overtly recessive and hypomorphic: each was able to substitute partially for endogenous non-muscle myosin II heavy chain in animals lacking zygotically produced heavy chain (but the penetrance of rescue was below Mendelian expectation). Moreover, each of the four mutant heavy chains exhibits dominant characteristics when expressed in a sensitized genetic background (flies heterozygous for RhoA mutations). Thus, these zip/MyoII(MYH9) alleles function, like certain other hypomorphic alleles, as excellent bait in screens for genetic interactors. Our conjecture is that these mutations in D. melanogaster behave comparably to their parent mutations in humans. We further characterized these zip/MyoII(MYH9) alleles, and found that all were capable of correct spatial and temporal localization in animals lacking zygotic expression of wild-type zip/MyoII. In vitro, we demonstrate that mutant heavy chains can dimerize with endogenous, wild-type heavy chains, fold into coiled-coil structures and assemble into higher-order structures. Our work further supports D. melanogaster as a model system for investigating the basis of human disease.

Gene expression profile of bioreactor-cultured cardiac cells: activation of morphogenetic pathways for tissue engineering

Cells grown in three-dimensional (3D) culture take on in vivo phenotypes and organize into tissue-like structures. Understanding the pathways and mechanisms contributing to this in vitro tissuegenesis is a critical goal of tissue engineering. To identify pathways relevant to cardiac tissue engineering, we compared mRNA expression profiles from bioreactor-cultured 3D aggregates of primary neonatal rat heart cells (NRHCs), which form layered structures similar to cardiac tissue, and standard plate-cultured NRHCs, which do not. In a series of two experiments, NRHCs were grown on solid microcarrier surfaces within clinostatically rotated polytetrafluoroethylene (PTFE) vessels and compared to parallel cultures grown on standard tissue culture plates without rotation. After 1, 4, and 6 days, gene expression profiles were analyzed using Affymetrix Rat Genome U34A (RG-U34A) arrays. The results were validated using real-time PCR, and the data set was filtered to generate a list of 93 probe sets that were substantially the same in replicate samples but substantially different between the bioreactor and plate groups. Cluster analysis indicated that the bioreactor and plate samples had similar expression patterns on day 1 but that these patterns diverged thereafter. Database for Annotation, Visualization, and Integrated Discovery (DAVID) analysis revealed a number of statistically significant gene groupings, including groups associated with muscle development and morphogenesis. Further analysis of the annotated gene list indicated that 13 of the 93 filtered genes were associated with endothelial cells, blood vessels, or angiogenesis. These results suggest that 3D aggregate culture of NRHCs in bioreactors is associated with the differential expression of morphogenic and angiogenic pathways similar to those seen during cardiac development.

Molecular prenatal diagnosis for hereditary distal arthrogryposis type 2B

Autosomal dominant distal arthrogryposes (DAs) are a group of muscle diseases characterized by congenital contractures of the limbs. Currently, prenatal diagnosis of DAs depends upon ultrasound examination during late gestation. Recently, five genes encoding fast switch proteins located at 9p13.2, 11p15.5 and 17q13.1 were identified. These included TPM2, TNNI2/TNNT3, and MYH3/MYH8. Last year, we discovered a novel heterozygous mutation c.523_525delAAG (p.K175del) in the TNNI2 gene, which encodes the isoform of troponinI, in a seven-generation Chinese family affected with distal arthrogryposis type 2B (DA2B). Here, we report the molecular prenatal diagnosis of 3 high-risk fetuses of two women in the family by two-point linkage inferential analysis and deletion detection of the TNNI2 gene with chorionic villus sampling (CVS) or amniocentesis. To our knowledge, this is the first description of molecular prenatal diagnosis for DAs.

Hereditary myosin myopathies

Hereditary myosin myopathies have emerged as a new group of muscle diseases with highly variable clinical features and onset during fetal development, childhood or adulthood. They are caused by mutations in skeletal muscle myosin heavy chain (MyHC) genes. Mutations have been reported in two of the three MyHC isoforms expressed in adult limb skeletal muscle: type I (slow/beta-cardiac MyHC; MYH7) and type IIa (MYH2). The majority of more than 200 dominant missense mutations in MYH7 are associated with hypertrophic/dilated cardiomyopathy without signs or symptoms of skeletal myopathy. Several mutations in two different parts of the slow/beta-cardiac MyHC rod region are associated with two distinct skeletal myopathies without cardiomyopathy: Laing early onset distal myopathy and myosin storage myopathy (MSM). However, early onset distal myopathy and MSM caused by MYH7 mutations may also occur together with cardiomyopathy. MSM affects proximal or scapuloperoneal muscles whereas Laing distal myopathy primarily affects the dorsiflexor muscles of the toes and ankles. MSM is morphologically characterized by subsarcolemmal accumulation of myosin in type 1 fibers, whereas Laing distal myopathy is associated with variable and unspecific muscle pathology, frequently with hypotrophic type 1 muscle fibers. A myopathy associated with a specific mutation in MYH2 is associated with congenital joint contractures and external ophthalmoplegia. The disease is mild in childhood but may be progressive in adulthood, with proximal muscle weakness affecting ambulation. Mutations in embryonic MyHC (MYH3) and perinatal MyHC (MYH8), which are myosin isoforms expressed during muscle development, are associated with distal arthrogryposis syndromes with no or minor muscle weakness. Clinical findings, muscle morphology and molecular genetics in hereditary myosin myopathies are summarized in this review.

A new distal arthrogryposis syndrome characterized by plantar flexion contractures

The distal arthrogryposis (DA) syndromes are a distinct group of disorders characterized by contractures of two or more different body areas. More than a decade ago, we revised the classification of DAs and distinguished several new syndromes. This revision has facilitated the identification of five genes (i.e., TNNI2, TNNT3, MYH3, MYH8, and TPM2) that encode components of the contractile apparatus of fast-twitch myofibers and cause DA syndromes. We now report on the phenotypic features of a novel DA disorder characterized primarily by plantar flexion contractures in a large five-generation Utah family. Contractures of hips, elbows, wrists, and fingers were much milder though they varied in severity among affected individuals. All affected individuals had normal neurological examinations; electromyography and creatinine kinase levels were normal on selected individuals. We have tentatively labeled this condition distal arthrogryposis type 10 (DA10).

Trismus-pseudocamptodactyly syndrome is caused by recurrent mutation ofMYH8

Trismus-pseudocamptodactyly syndrome (TPS) is a rare autosomal dominant distal arthrogryposis (DA) characterized by an inability to open the mouth fully (trismus) and an unusual camptodactyly of the fingers that is apparent only upon dorsiflexion of the wrist (i.e., pseudocamptodactyly). TPS is also known as Dutch-Kentucky syndrome because a Dutch founder mutation is presumed to be the origin of TPS cases in the Southeast US, including Kentucky. To date only a single mutation, p.R674Q, in MYH8 has been reported to cause TPS. Several individuals with this mutation also had a so-called "variant" of Carney complex, suggesting that the pathogenesis of TPS and Carney complex might be shared. We screened MYH8 in four TPS pedigrees, including the original Dutch family in which TPS was reported. All four TPS families shared the p.R674Q substitution. However, haplotype analysis revealed that this mutation has arisen independently in North American and European TPS pedigrees. None of the individuals with TPS studied had features of Carney complex, and p.R674Q was not found in 49 independent cases of Carney complex that were screened. Our findings show that distal arthrogryposis syndromes share a similar pathogenesis and are, in general, caused by disruption of the contractile complex of muscle.

Carbamazepine treatment of agitation in Alzheimer's outpatients refractory to neuroleptics

Genome-wide association studies suggest that common genetic variants explain only a small fraction of heritable risk for common diseases, raising the question of whether rare variants account for a significant fraction of unexplained heritability1,2. While DNA sequencing costs have fallen dramatically3, they remain far from what is necessary for rare and novel variants to be routinely identified at a genome-wide scale in large cohorts. We have therefore sought to develop second-generation methods for targeted sequencing of all protein-coding regions (`exomes'), to reduce costs while enriching for discovery of highly penetrant variants. Here we report on the targeted capture and massively parallel sequencing of the exomes of twelve humans. These include eight HapMap individuals representing three populations4, and four unrelated individuals with a rare dominantly inherited disorder, Freeman-Sheldon syndrome (FSS)5. We demonstrate the sensitive and specific identification of rare and common variants in over 300 megabases (Mb) of coding sequence. Using FSS as a proof-of-concept, we show that candidate genes for monogenic disorders can be identified by exome sequencing of a small number of unrelated, affected individuals. This strategy may be extendable to diseases with more complex genetics through larger sample sizes and appropriate weighting of nonsynonymous variants by predicted functional impact.