Early onset collagen VI myopathies: Genetic and clinical correlations.
OBJECTIVE
Mutations in the genes encoding the extracellular matrix protein collagen VI (ColVI) cause a spectrum of disorders with variable inheritance including Ullrich congenital muscular dystrophy, Bethlem myopathy, and intermediate phenotypes. We extensively characterized, at the clinical, cellular, and molecular levels, 49 patients with onset in the first 2 years of life to investigate genotype-phenotype correlations.


METHODS
Patients were classified into 3 groups: early-severe (18%), moderate-progressive (53%), and mild (29%). ColVI secretion was analyzed in patient-derived skin fibroblasts. Chain-specific transcript levels were quantified by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), and mutation identification was performed by sequencing of complementary DNA.


RESULTS
ColVI secretion was altered in all fibroblast cultures studied. We identified 56 mutations, mostly novel and private. Dominant de novo mutations were detected in 61% of the cases. Importantly, mutations causing premature termination codons (PTCs) or in-frame insertions strikingly destabilized the corresponding transcripts. Homozygous PTC-causing mutations in the triple helix domains led to the most severe phenotypes (ambulation never achieved), whereas dominant de novo in-frame exon skipping and glycine missense mutations were identified in patients of the moderate-progressive group (loss of ambulation).


CONCLUSIONS
This work emphasizes that the diagnosis of early onset ColVI myopathies is arduous and time-consuming, and demonstrates that quantitative RT-PCR is a helpful tool for the identification of some mutation-bearing genes. Moreover, the clinical classification proposed allowed genotype-phenotype relationships to be explored, and may be useful in the design of future clinical trials.
Inserm, U582, Paris, France.
Laura
L
Briñas
Pascale
P
Richard
Susana
S
Quijano-Roy
Corine
C
Gartioux
Céline
C
Ledeuil
Emmanuelle
E
Lacène
Samira
S
Makri
Ana
A
Ferreiro
Svetlana
S
Maugenre
Haluk
H
Topaloglu
Göknur
G
Haliloglu
Isabelle
I
Pénisson-Besnier
Pierre-Yves
PY
Jeannet
Luciano
L
Merlini
Carmen
C
Navarro
Annick
A
Toutain
Denys
D
Chaigne
Isabelle
I
Desguerre
Christine
C
de Die-Smulders
Murielle
M
Dunand
Bernard
B
Echenne
Bruno
B
Eymard
Thierry
T
Kuntzer
Kim
K
Maincent
Michèle
M
Mayer
Ghislaine
G
Plessis
François
F
Rivier
Filip
F
Roelens
Tanya
T
Stojkovic
Ana Lía
AL
Taratuto
Fabiana
F
Lubieniecki
Soledad
S
Monges
Christine
C
Tranchant
Louis
L
Viollet
Norma B
NB
Romero
Brigitte
B
Estournet
Pascale
P
Guicheney
Valérie
V
Allamand
D000293:Adolescent; D000328:Adult; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D024143:Collagen Type VII / Q000235:genetics* / Q000378:metabolism*; D005060:Europe; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D005820:Genetic Testing / Q000379:methods; D005998:Glycine / Q000235:genetics; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D009135:Muscular Diseases / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D013223:Statistics as Topic; D055815:Young Adult
D024143:Collagen Type VII; D005998:Glycine