Novel mutations in TPM2 and PIEZO2 are responsible for distal arthrogryposis (DA) 2B and mild DA in two Chinese families.

BACKGROUND: Distal arthrogryposis (DA) is a group of clinically and genetically heterogeneous disorders that involve multiple congenital limb contractures and comprise at least 10 clinical subtypes. Here, we describe our findings in two Chinese families: Family 1 with DA2B (MIM 601680) and Family 2 with mild DA. METHODS: To map the disease locus, two-point linkage analysis was performed with microsatellite markers closed to TPM2, TNNI2/TNNT3 and TNNC2. In Family 1, a positive LOD (logarithm of odds) score was only obtained at the microsatellite marker close to TPM2 and mutation screening was performed using direct sequencing of TPM2 in the proband. In Family 2, for the LOD score that did not favor linkage to any markers, whole-exome sequencing (WES) was performed on the proband. PCR-restriction fragment length polymorphism (RFLP) and bioinformatics analysis were then applied to identify the pathogenic mutations in two families. In order to correlate genotype with phenotype in DA, retrospective analyses of phenotypic features according to the TPM2 and PIEZO2 mutation spectrums were carried out. RESULTS: A heterozygous missense mutation c.308A > G (p.Q103R) in TPM2 in Family 1, and a novel variation c.8153G > A (p.R2718Q) in PIEZO2 in Family 2 were identified. Each of the two novel variants was co-segregated with the DA manifestations in the corresponding family. Bioinformatics analysis from several tools supported the pathogenicity of the mutations. Furthermore, our study suggests that there is no relation between the types or locations of TPM2 mutations and the clinical characteristics, and that different inheritance modes and mutation types concerning PIEZO2 cause distinct clinical manifestations. CONCLUSIONS: We report two novel mutations within TPM2 and PIEZO2 responsible for DA2B and mild DA in two Chinese families, respectively. Our study expands the spectrum of causal mutations in the TPM2 and PIEZO2 genes.

Expanding the MYBPC1 phenotypic spectrum: a novel homozygous mutation causes arthrogryposis multiplex congenita.

Arthrogryposis multiplex congenita (AMC) is characterized by heterogeneous nonprogressive multiple joint contractures appearing at birth. We present a consanguineous Israeli-Druze family with several members presenting with AMC. A variable intra-familial phenotype and pected autosomal recessive inheritance prompted molecular diagnosis by whole-exome sequencing. Variant analysis focused on rare homozygous changes, revealed a missense variant in MYBPC1, NM_002465:c.556G>A (p.E286K), affecting the last nucleotide of Exon 8. This novel variant was not observed in the common variant databases and co-segregated as expected within the extended family. MYBPC1 encodes a slow skeletal muscle isoform, essential for muscle contraction. Heterozygous mutations in this gene are associated with distal arthrogryposis types 1b and 2, whereas a homozygous nonsense mutation is implicated in one family with lethal congenital contractural syndrome 4. We present a novel milder MYBPC1 homozygous phenotype.

Review of perinatal management of arthrogryposis at a large UK teaching hospital serving a multiethnic population.

OBJECTIVE: To review the prevalence and perinatal management of cases of arthrogryposis delivering at our hospital over a 6-year period. METHODS: This was a retrospective review of cases of arthrogryposis managed at a UK teaching hospital. Cases were identified from the regional congenital anomalies register and departmental databases. Case notes were reviewed and analysed. RESULTS: From 2002 to 2007, there were 27 cases of arthrogryposis. Sixteen (59.3%) were Caucasians, 7(25.9%) Asians and 4(14.8%) Afro-Caribbean; 17(63%) were nulliparous. In eight (29.6%) cases, there was a family history of congenital anomalies. Three had previously affected siblings and in three cases the parents were affected with arthrogryposis. Five (18.5%) were from consanguineous families. Eighteen (66.7%) cases were diagnosed prenatally at a mean gestational age of 21 weeks. Twelve (57%) were delivered by caesarean section. There were 18 live births. Sixteen (59%) cases were reviewed by clinical geneticist. Following detailed review and investigation including post-mortems, 20 (74%) of our cases had a formal diagnosis or likely cause identified. CONCLUSIONS: Suspected cases of arthrogryposis require multi-disciplinary management to optimise the possibility of making a diagnosis and providing parents with accurate information to enable them to make informed choices regarding the pregnancy and providing information regarding likelihood of recurrence.

Molecular investigations to improve diagnostic accuracy in patients with ARC syndrome.

Arthrogryposis, Renal dysfunction and Cholestasis (ARC) syndrome is a multi-system autosomal recessive disorder caused by germline mutations in VPS33B. The detection of germline VPS33B mutations removes the need for diagnostic organ biopsies (these carry a>50% risk of life-threatening haemorrhage due to platelet dysfunction); however, VPS33B mutations are not detectable in approximately 25% of patients. In order further to define the molecular basis of ARC we performed mutation analysis and mRNA and protein studies in patients with a clinical diagnosis of ARC. Here we report novel mutations in VPS33B in patients from Eastern Europe and South East Asia. One of the mutations was present in 7 unrelated Korean patients. Reduced expression of VPS33B and cellular phenotype was detected in fibroblasts from patients clinically diagnosed with ARC with and without known VPS33B mutations. One mutation-negative patient was found to have normal mRNA and protein levels. This patient's clinical condition improved and he is alive at the age of 2.5 years. Thus we show that all patients with a classical clinical course of ARC had decreased expression of VPS33B whereas normal VPS33B expression was associated with good prognosis despite initial diagnosis of ARC.

A gene for arthrogryposis multiplex congenita neuropathic type is linked to D5S394 on chromosome 5qter.

Arthrogryposis multiplex congenita (AMC) is a heterogeneous-symptom complex characterized by joint contractures at birth that involve more than one part of the body. We performed a genetic-linkage study of one large Israeli-Arab inbred kindred showing autosomal recessive inheritance of AMC neuropathic type that had been recently investigated by our group. After analysis of approximately 80% of the genome, D5S1456, which showed no increased homozygosity, showed increased genotype sharing in affected individuals. Linkage analysis in all family members revealed linkage between AMC and D5S1456 on chromosome 5qter (maximum LOD score 5.3 at recombination fraction .001). Analysis of additional markers in this region places the gene causing AMC in this family between D5S1456 and D5S498.

German syndrome in sibs.

We present a male-female sib pair born to Ashkenazi Jewish parents with "arthrogryposis," hypotonia-hypokinesia sequence and lymphedema. Of all the "arthrogryposis" hypotonia syndromes, the condition in these sibs appears to be most like that of the patients of German et al [1975] and the patient of Salmon [1978]. They appear to be the first sib pair with German syndrome, which suggests autosomal recessive inheritance. Three of the four known families with affected children have been Ashkenazi Jews.