RESUMO
Recessive mutations of MYO7A, encoding unconventional myosin VIIA, can cause either a deaf-blindness syndrome (type 1 Usher syndrome; USH1B) or nonsyndromic deafness (DFNB2). In our study, deafness segregating as a recessive trait in 24 consanguineous families showed linkage to markers for the DFNB2/USH1B locus on chromosome 11q13.5. A total of 23 of these families segregate USH1 due to 17 homozygous mutant MYO7A alleles, of which 14 are novel. One family segregated nonsyndromic hearing loss DFNB2 due to a novel three-nucleotide deletion in an exon of MYO7A (p.E1716del) encoding a region of the tail domain. We hypothesized that DFNB2 alleles of MYO7A have residual myosin VIIA. To address this question we investigated the effects of several mutant alleles by making green fluorescent protein (GFP) tagged cDNA expression constructs containing engineered mutations of mouse Myo7a at codons equivalent to pathogenic USH1B and DFNB2 alleles of human MYO7A. We show that in transfected mouse hair cells an USH1B mutant GFP-myosin VIIa does not localize properly to inner ear hair cell stereocilia. However, a GFP-myosin VIIa protein engineered to have an equivalent DFNB2 mutation to p.E1716del localizes correctly in transfected mouse hair cells. This finding is consistent with the hypothesis that p.E1716del causes a less severe phenotype (DFNB2) than the USH1B-associated alleles because the resulting protein retains some degree of normal function.
Assuntos
Surdez/genética , Dineínas/genética , Mutação , Miosinas/genética , Adulto , Alelos , Sequência de Aminoácidos , Animais , Composição de Bases , Cromossomos Humanos Par 11/genética , Consanguinidade , DNA Complementar/genética , Surdez/metabolismo , Surdez/fisiopatologia , Dineínas/química , Dineínas/metabolismo , Éxons , Feminino , Genes Recessivos , Ligação Genética , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Células Ciliadas Auditivas Internas/metabolismo , Humanos , Cinética , Masculino , Camundongos , Pessoa de Meia-Idade , Modelos Moleculares , Dados de Sequência Molecular , Miosina VIIa , Miosinas/química , Miosinas/metabolismo , Linhagem , Fenótipo , Conformação Proteica , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Deleção de Sequência , Homologia de Sequência de Aminoácidos , Transfecção , Síndromes de Usher/genética , Síndromes de Usher/metabolismo , Síndromes de Usher/fisiopatologiaRESUMO
A severe form of autosomal recessive retinitis pigmentosa (arRP) was identified in a large Pakistani family ascertained in the Punjab province of Pakistan. All affected individuals in the family had night blindness in early childhood, early complete loss of useful vision, and typical RP fundus changes plus macular degeneration. After exclusion of known arRP loci, a genome-wide scan was performed using microsatellite markers at about 10 cM intervals and calculating two-point lod scores. PCR cycle dideoxynucleotide sequencing was used to sequence candidate genes inside the linked region for mutations. RP in this family shows linkage to markers in a 10.5 cM (8.9 Mbp) region of chromosome 1p13.3-p21.2 between D1S2896 and D1S457. D1S485 yields the highest lod score of 6.54 at theta=0. Sequencing the exons and intron-exon boundaries of five candidate genes and six ESTs in this region, OLFM3, GNAI3, LOC126987, FLJ25070, DKFZp586G0123, AV729694, BU662869, BU656110, BU171991, BQ953690, and CA397743, did not identify any causative mutations. This novel locus lies approximately 4.9 cM (7.1 Mbp) from ABCA4, which is excluded from the linked region. Identification and study of this gene may help to elucidate the phenotypic diversity of arRP mapping to this region.
