Genomic rearrangements in the CFTR gene: extensive allelic heterogeneity and diverse mutational mechanisms.
Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR/ABCC7). Despite the extensive and enduring efforts of many CF researchers over the past 14 years, up to 30% of disease alleles still remain to be identified in some populations. It has long been suggested that gross genomic rearrangements could account for these unidentified alleles. To date, however, only a few large deletions have been found in the CFTR gene and only three have been fully characterized. Here, we report the first systematic screening of the 27 exons of the CFTR gene for large genomic rearrangements, by means of the quantitative multiplex PCR of short fluorescent fragments (QMPSF). A well-characterized cohort of 39 classical CF patients carrying at least one unidentified allele (after extensive and complete screening of the CFTR gene by both denaturing gradient gel electrophoresis and denaturing high-performance liquid chromatography) participated in this study. Using QMPSF, some 16% of the previously unidentified CF mutant alleles were identified and characterized, including five novel mutations (one large deletion and four indels). The breakpoints of these five mutations were precisely determined, enabling us to explore the underlying mechanisms of mutagenesis. Although non-homologous recombination may be invoked to explain all five complex lesions, each mutation appears to have arisen through a different mechanism. One of the indels was highly unusual in that it involved the insertion of a short 41 bp sequence with partial homology to a retrotranspositionally-competent LINE-1 element. The insertion of this ultra-short LINE-1 element (dubbed a "hyphen element") may constitute a novel type of mutation associated with human genetic disease.
Audrézet
Marie-Pierre
MP
INSERM U613, Génétique Moléculaire et Génétique Epidémiologique, Centre Hospitalier Universitaire, Brest, France.
Chen
Jian-Min
JM
Raguénès
Odile
O
Chuzhanova
Nadia
N
Giteau
Karine
K
Le Maréchal
Cédric
C
Quéré
Isabelle
I
Cooper
David N
DN
Férec
Claude
C
D000483:Alleles; D001483:Base Sequence; D019457:Chromosome Breakage; D003550:Cystic Fibrosis / Q000235:genetics*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics*; D015894:Genome, Human; D006801:Humans; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D016133:Polymerase Chain Reaction; D011995:Recombination, Genetic; D016415:Sequence Alignment; D017384:Sequence Deletion
C505032:CFTR protein, human; D019005:Cystic Fibrosis Transmembrane Conductance Regulator