A homozygous COL6A2 intron mutation causes in-frame triple-helical deletion and nonsense-mediated mRNA decay in a patient with Ullrich congenital muscular dystrophy

Abstract

Ullrich congenital muscular dystrophy (UCMD) is a severe disorder caused, in most cases, by a deficiency in collagen VI microfibrils. Recessive mutations in two of the three collagen VI genes, COL6A2 and COL6A3, have been identified in eight of the nine UCMD patients reported thus far. A heterozygous COL6A1 gene deletion, resulting in a mutant protein that exerts a dominant negative effect, has recently been described in a severely affected UCMD patient. Here we describe a patient in whom reverse transcription-PCR analysis of fibroblast RNA suggested a heterozygous in-frame deletion of exon 13 in the triple-helical domain of COL6A2, which is predicted to be dominantly acting. However, a homozygous A fi G mutation at À10 of intron 12 was found in the genomic DNA. The intron mutation activated numerous cryptic splice acceptor sites, generating normal and exon 13-deleted COL6A2 mRNA, and multiple aberrant transcripts containing frameshifts that were degraded through a nonsense-mediated decay mechanism. Northern analysis indicated diminished COL6A2 mRNA expression as the primary pathogenic mechanism in this UCMD patient. Our results underscore the importance of multifaceted analyses in the accurate molecular diagnosis and interpretation of genotype-phenotype correlations of UCMD.

A refined diagnostic algorithm for Bethlem myopathy

“…[9][10][11][12] In BM, however, there is significant clinical overlap with other contractural muscular dystrophies, and standard collagen VI IHC of muscle is uninformative. The gold standard diagnostic test for BM is molecular genetic testing, but the large size of the collagen VI genes (107 coding exons, 150 kb genomic DNA) makes it expensive and time-consuming.…”

Primary collagen VI deficiency is the second most common congenital muscular dystrophy in Japan

“…26 Furthermore, all the dominant mutations that we identified and those previously reported were located in the N-terminal side from the cysteine residue in the THD. 5,6,11,27 The cysteine residues are believed to be crucial in the formation of the triple helical structures in collagen VI. 28 Thus the substitutions or deletions in the N-terminal side from the cysteine residue are likely to affect the conformation around the cysteine residues and, subsequently, the formation of the functional higher structure of collagen VI complex.…”

Identification and characterization of novel collagen VI non-canonical splicing mutations causing ullrich congenital muscular dystrophy

“…In contrast, UCMD3 had similar levels of normal and mutant COL6A1 mRNAs, and 50% of the α1(VI) chain is expected to be mutant. Considering the multi-step assembly of collagen VI occurring before secretion (Pan et al, 2003;Lucarini et al, 2005) the defects caused by a mutant chain are likely to be amplified during the assembly process and may severely impair collagen VI secretion, as observed in UCMD3.…”