A refined diagnostic algorithm for Bethlem myopathy.
OBJECTIVE
Mutations in COL6A1, COL6A2, and COL6A3, the genes that encode the extracellular matrix component collagen VI, lead to Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD). Unlike UCMD, BM is difficult to diagnose because of its clinical overlap with other contractural phenotypes and the lack of sensitivity of standard muscle biopsy immunohistochemical diagnostic techniques.


METHODS
We appraised two potential techniques for the diagnosis of BM: dual immunofluorescence (IF) for collagen VI and basal lamina-located perlecan in muscle, and immunofluorescent labeling of collagen VI in skin biopsy-derived fibroblast cultures, which was conducted in 40 patients by blinded investigators and correlated with genetic findings.


RESULTS
Dual IF was indistinguishable from normal controls in most BM patients. However, abnormalities in the IF labeling pattern of collagen VI were detected in more than 78% of genetically confirmed BM patient fibroblast cell lines. In addition, in a group of patients with unknown diagnosis studied prospectively, the fibroblast IF technique was highly predictive of the presence of a COL6A mutation, providing a positive predictive value of 75%, a sensitivity and negative predictive value of 100%, and a specificity of 63%.


CONCLUSIONS
Immunofluorescent labeling of collagen VI in fibroblast cultures is a useful addition to current diagnostic services for Bethlem myopathy (BM). It can be used to guide molecular genetic testing, the gold standard diagnostic technique for BM, in a cost-effective and time-saving manner.
Hicks
D
D
Institute of Human Genetics, Newcastle University, Newcastle upon Tyne, NE1 3BZ, Great Britain.
Lampe
A K
AK
Barresi
R
R
Charlton
R
R
Fiorillo
C
C
Bonnemann
C G
CG
Hudson
J
J
Sutton
R
R
Lochmüller
H
H
Straub
V
V
Bushby
K
K
D000465:Algorithms; D002478:Cells, Cultured; D024142:Collagen Type VI / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism*; D005455:Fluorescent Antibody Technique / Q000379:methods / Q000592:standards; D019812:Heparan Sulfate Proteoglycans / Q000032:analysis / Q000276:immunology / Q000378:metabolism; D006801:Humans; D008967:Molecular Biology / Q000379:methods; D025202:Molecular Diagnostic Techniques / Q000379:methods / Q000592:standards; D018482:Muscle, Skeletal / Q000276:immunology / Q000378:metabolism* / Q000503:physiopathology; D009135:Muscular Diseases / Q000175:diagnosis* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012189:Retrospective Studies; D016037:Single-Blind Method; D012867:Skin / Q000166:cytology / Q000276:immunology / Q000378:metabolism
D024142:Collagen Type VI; D019812:Heparan Sulfate Proteoglycans; C071927:perlecan