Identification of a novel pathogenic mutation of the MYH3 gene in a family with distal arthrogryposis type 2B.

Distal arthrogryposis (DA) type 2B (DA2B) is an autosomal dominant congenital disorder, characterized by camptodactyly, thumb adduction, ulnar deviation and facial features, including small mouth, down­slanting palpebral fissure and slight nasolabial fold. It has been reported that four genes are associated with DA2B, including troponin I, fast­twitch skeletal muscle isoform, troponin T3, fast skeletal, myosin heavy chain 3 (MYH3) and tropomyosin 2, which are all associated with embryonic limb morphogenesis and skeletal muscle contraction. In the present study, three affected family members and five unaffected individuals were identified through clinical and radiological assessment. Genomic DNA was obtained from the three patients, which then underwent whole­exome sequencing, and candidate mutations were verified by Sanger sequencing in all available family members and 100 healthy volunteers. Then, the spatial models of embryonic MYH were further constructed. In the clinic, the three patients recruited to the present study were diagnosed with DA2B. Mutation analysis indicated that there was a novel heterogeneous missense mutation c.2506 A>G (p.K836E) in the MYH3 gene among the affected individuals, which was highly conserved and was not identified in the unaffected family members and healthy controls. Furthermore, protein modeling revealed that the altered position interacted with regulatory light chain. Thus, the present study identified a novel pathogenic mutation of the MYH3 gene in a Chinese family with DA2B, which expanded the mutational spectrum of MYH3 and provided additional information regarding the association between mutation locations and different types of DA.

Identification of a novel mutation of the NTRK1 gene in patients with congenital insensitivity to pain with anhidrosis (CIPA).

INTRODUCTION: Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive disorder resulting from NTRK1 mutation. Over 105 NTRK1 mutations have been reported in CIPA patients worldwide. The causative NTRK1 mutations lead to loss of function of the TrkA protein, an important ligand for nerve growth factor (NGF), and therefore induce various clinical phenotypes associated with neuron maturation defects. MATERIALS AND METHODS: Three patients from unrelated families with CIPA were subjected to detailed clinical examinations. Blood samples were collected from all the patients and their available family members, as well as 200 healthy volunteers. Sanger sequencing for all the exons and splicing sites of NTRK1 was performed on all samples. The phenotype-genotype relationship and genetic epidemiology of Chinese CIPA patients were also analysed. RESULTS: A total of four different NTRK1 mutations [c.851-33T>A, c.44G>A (p.Trp15*), c.287+2dupT, c.1549G>C (p.Gly517Arg)] were identified in these families, and c.1549G>C (p.Gly517Arg) was a novel mutation that had not been reported previously. The 'mild' manifestations observed in patients with c.851-33T>A indicated this mutation as a 'mild' mutation. After reviewing studies reporting mutations in Chinese CIPA patients, we speculate the mutation c.851-33T>A is one of the founder mutations in the Chinese population. CONCLUSIONS: Our research expanded the spectrum of the NTRK1 mutations associated with CIPA patients, provided additional clues relating to the phenotype-genotype relationship in CIPA, and summarized the features of the genetic epidemiology of CIPA in the Chinese ethnic group.