title: Exon skipping mutations in collagen VI are common and are predictive for severity and inheritance.
abstract: Mutations in the genes encoding collagen VI (COL6A1, COL6A2, and COL6A3) cause Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD), two related conditions of differing severity. BM is a relatively mild dominantly inherited disorder characterized by proximal weakness and distal joint contractures. UCMD was originally regarded as an exclusively autosomal recessive condition causing severe muscle weakness with proximal joint contractures and distal hyperlaxity. We and others have subsequently modified this model when we described UCMD patients with heterozygous in-frame deletions acting in a dominant-negative way. Here we report 10 unrelated patients with a UCMD clinical phenotype and de novo dominant negative heterozygous splice mutations in COL6A1, COL6A2, and COL6A3 and contrast our findings with four UCMD patients with recessively acting splice mutations and two BM patients with heterozygous splice mutations. We find that the location of the skipped exon relative to the molecular structure of the collagen chain strongly correlates with the clinical phenotype. Analysis by immunohistochemical staining of muscle biopsies and dermal fibroblast cultures, as well as immunoprecipitation to study protein biosynthesis and assembly, suggests different mechanisms each for exon skipping mutations underlying dominant UCMD, dominant BM, and recessive UCMD. We provide further evidence that de novo dominant mutations in severe UCMD occur relatively frequently in all three collagen VI chains and offer biochemical insight into genotype-phenotype correlations within the collagen VI-related disorders by showing that severity of the phenotype depends on the ability of mutant chains to be incorporated in the multimeric structure of collagen VI.
authors: Division of Neurology, The Children's Hospital of Philadelphia and University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA. anneklampe@doctors.org.uk
authors: A K
authors: AK
authors: Lampe
authors: Y
authors: Y
authors: Zou
authors: D
authors: D
authors: Sudano
authors: K K
authors: KK
authors: O'Brien
authors: D
authors: D
authors: Hicks
authors: S H
authors: SH
authors: Laval
authors: R
authors: R
authors: Charlton
authors: C
authors: C
authors: Jimenez-Mallebrera
authors: R-Z
authors: RZ
authors: Zhang
authors: R S
authors: RS
authors: Finkel
authors: G
authors: G
authors: Tennekoon
authors: G
authors: G
authors: Schreiber
authors: M S
authors: MS
authors: van der Knaap
authors: H
authors: H
authors: Marks
authors: V
authors: V
authors: Straub
authors: K M
authors: KM
authors: Flanigan
authors: M-L
authors: ML
authors: Chu
authors: F
authors: F
authors: Muntoni
authors: K M D
authors: KM
authors: Bushby
authors: C G
authors: CG
authors: Bönnemann
mesh_terms: D002478:Cells, Cultured; D024142:Collagen Type VI / Q000235:genetics* / Q000378:metabolism; D004252:DNA Mutational Analysis; D005091:Exons; D005347:Fibroblasts / Q000378:metabolism; D017353:Gene Deletion; D006801:Humans; D018482:Muscle, Skeletal / Q000378:metabolism; D009136:Muscular Dystrophies / Q000235:genetics*; D009154:Mutation; D012326:RNA Splicing; D012720:Severity of Illness Index; D012867:Skin / Q000166:cytology
chemical_list: C504344:COL6A2 protein, human; D024142:Collagen Type VI