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.

Pilocytic astrocytoma in a child with Noonan syndrome.

Noonan syndrome (NS; MIM 163950) is an autosomal dominant dysmorphic syndrome characterized by distinct facial features, cardiac anomalies, short stature, and motor delay. Activating mutations in PTPN11, encoding the protein tyrosine phosphatase SHP2, are associated with about 50% of cases. Mutations in other genes in the RAS/mitogen-activated protein kinase signaling pathway are responsible for many of the remainder of cases. While mutations in this pathway are found in a variety of malignancies, including solid tumors, there are few reports of solid tumors in individuals with NS. We report here a patient with PTPN11 mutation-associated NS and a pilocytic astrocytoma.

Asymmetric lower-limb malformations in individuals with homeobox PITX1 gene mutation.

Clubfoot is one of the most common severe musculoskeletal birth defects, with a worldwide incidence of 1 in 1000 live births. In the present study, we describe a five-generation family with asymmetric right-sided predominant idiopathic clubfoot segregating as an autosomal-dominant condition with incomplete penetrance. Other lower-limb malformations, including patellar hypoplasia, oblique talus, tibial hemimelia, developmental hip dysplasia, and preaxial polydactyly, were also present in some family members. Genome-wide linkage analysis with Affymetrix GeneChip Mapping 10K mapping data from 13 members of this family revealed a multipoint LOD(max) of 3.31 on chromosome 5q31. A single missense mutation (c.388G-->A) was identified in PITX1, a bicoid-related homeodomain transcription factor critical for hindlimb development, and segregated with disease in this family. The PITX1 E130K mutation is located in the highly conserved homeodomain and reduces the ability of PITX1 to transactivate a luciferase reporter. The PITX1 E130K mutation also suppresses wild-type PITX1 activity in a dose-dependent manner, suggesting dominant-negative effects on transcription. The propensity for right-sided involvement in tibial hemimelia and clubfoot suggests that PITX1, or pathways involving PITX1, may be involved in their etiology. Implication of a gene involved in early limb development in clubfoot pathogenesis also suggests additional pathways for future investigations of idiopathic clubfoot etiology in humans.