Molecular and in silico analyses of the full-length isoform of usherin identify new pathogenic alleles in Usher type II patients.
The usherin gene (USH2A) has been screened for mutations causing Usher syndrome type II (USH2). Two protein isoforms have been identified: a short isoform of 1,546 amino acids and a more recently recognized isoform extending to 5,202 amino acids. We have screened the full length by genomic sequencing. We confirm that many mutations occur in the exons contributing solely to the longer form. USH2 is an autosomal recessive disorder and, in contrast to previous studies, both mutations were identified in 23 patients and a single mutation in 2 out of 33 patients. A total of 34 distinct mutated alleles were identified, including one complex allele with three variants and another with two. A total of 27 of these are novel, confirming that most mutations in usherin are private. Many of the mutations will lead to prematurely truncated protein but as there are a substantial number of missense variants, we have used in silico analysis to assess their pathogenicity. Evidence that they are disease-causing has been produced by protein alignments and three-dimensional (3D) structural predictions when possible. We have identified a previously unrecognized cysteine rich structural domain, containing 12 dicysteine repeats, and show that three missense mutations result in the loss of one of a pair of the defining cysteine-cysteine pairs.
Baux
David
D
Centre Hospitalier Universitaire (CHU) Montpellier, Laboratoire de Génétique Moléculaire, Montpellier, France.
Larrieu
Lise
L
Blanchet
Catherine
C
Hamel
Christian
C
Ben Salah
Safouane
S
Vielle
Anne
A
Gilbert-Dussardier
Brigitte
B
Holder
Muriel
M
Calvas
Patrick
P
Philip
Nicole
N
Edery
Patrick
P
Bonneau
Dominique
D
Claustres
Mireille
M
Malcolm
Sue
S
Roux
Anne-Françoise
AF
D000293:Adolescent; D000328:Adult; D000368:Aged; D000483:Alleles; D000595:Amino Acid Sequence; D002648:Child; D019295:Computational Biology / Q000379:methods*; D003545:Cysteine; D004252:DNA Mutational Analysis; D016326:Extracellular Matrix Proteins / Q000737:chemistry / Q000235:genetics*; D005838:Genotype; D006801:Humans; D008875:Middle Aged; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D052245:Usher Syndromes / Q000235:genetics*
D016326:Extracellular Matrix Proteins; D020033:Protein Isoforms; C112735:USH2A protein, human; D003545:Cysteine