G.P.154: Mutations in ECEL1 lead to distal arthrogryposis type 5D

Abstract

Distal arthrogryposis (DA) is a clinically and genetically heterogeneous condition with mutations in at least five genes encoding for sarcomeric proteins (TNN12, TNNT3, TPM2, MYH3 and MYH8) implicated to date. A significant proportion of cases remain genetically uncharacterised. Here we describe 4 members from a 3 generation consanguineous Irish family that presented with a congenital myopathy resembling King-Denborough syndrome (KDS), characterized by clinical features of ptosis and distal arthrogryposis, and cores on muscle biopsy. Through collaboration with The Sanger Centre as part of the UK10K project, we exome screened these subjects and were able to identify a segregating homozygous misssense mutation in exon 2 of the Endothelin converting enzyme like 1 (ECEL1) gene, recently found to be responsible for DA5D. Population screening enabled us to find two additional DA families that harboured causative variants ECEL1 exons 2 and 15, respectively, reinforcing the notion of a causative link between ecel1 dysfunction and the DA's. ECEL1 encodes for a type2 transmembrane M13 metallopeptidase with an as yet unidentified substrate, localised to the endoplasmic reticulum and plasma membrane of the central nervous system (CNS). The ecel1 protein is also expressed in skeletal muscle and thought to participate in the formation of the neuromuscular junction (NMJ), but its precise function is currently unknown. We therefore embarked on protein function assays in zebrafish morphants and ECEL1-mutated patient fibroblasts. In particular, we knocked down (KD) ecel1 in zebra fish embryo applying a morpholino approach and found a gross defect in body axis curvature leading to perturbed functional abilities. Microscopic examination revealed disorganised/detached myofibres that have intact sarcolemma. (We have also obtained a zebrafish ecel1 knock out (KO) model achieved by insertion of a null allele by chemical mutagenesis. This model does not exhibit the same trunk curvatur.