Résumé :
|
The collagen VI related myopathies include Bethlem (BM) and Ullrich (UCMD) muscular dystrophies, a pure limb girdle presentation (LGMD) and the Myosclerosis Myopathy. Despite of extensive sequencing procedures, either at genomic or cDNA level, the detection rate of COL6 mutations analysis varies from 60-65% to 75-79% in UCMD and BM respectively. We have approached the molecular characterization of 47 patients with clinical/ immunohistochemical diagnosis of UCMD (23), BM (21), LGMD (1) and Myosclerosis (2). To date, we have identified by sequencing 20 different mutations in 17 unrelated patients (12 UCMD; 3 BM, 1 LGMD and 1 Myosclerosis). The majority of the identified mutations is novel and preferentially involves the TH and C-terminal domains of COL6A2 gene (11out of 20). Differently, the mutations identified in COL6A1 and COL6A3 genes (6 and 3 respectively), are clustered in the NH and TH-domains. We have identified 8 missense and 2 nonsense changes, 5 small insertions/deletions and 5 intronic variations affecting splicing. Furthermore, we have designed an innovative Comparative Genomic Hybridization array (aCGH), based on Agilent technology. The coding and regulatory regions of COL6A genes were included in the array as well as 10 additional genes selected on the basis of their functional relationship with collagen VI and therefore possible candidate as UCMD/BM genes. The COL6A array was preliminary tested on four UCMD patients and a 2.5 kb deletion in COL6A2 intron 1 was identified, occurring in a UCMD patient in compound heterozygosity with a small deletion in COL6A2 exon 28, inherited from the healthy mother. We are currently validating the aCGH finding by Real-time PCR. RNA analysis from cultured fibroblast of the UCMD patient showed the presence of the mutated transcript only. The occurrence of monoallaelic transcription could be related to the intronic deletion identified by aCGH approach, possibly removing critical COL6A2 regulatory elements.
|