RESUMEN
Fragile X syndrome is the most frequent hereditary cause of mental retardation after Down syndrome. Expansion of CGG repeats in the 5' UTR of the fragile X mental retardation gene 1 (FMR1) causes gene inactivation in most of the cases. The FMR1 gene is classified into normal 5-44; gray zone 45-54; premutation 55 to <200; and full mutation ≥ 00 repeats. Precise sizing of FMR1 alleles is important to understand their variation, predisposition, and for genetic counseling. Meta-analysis reveals prevalence of premutation carriers as 1 in 259. No such reports are available in India. About 705 women from Tamil Nadu, South India, were screened for the FMR1 allelic variation by using radioactive polymerase chain reaction-polyacrylamide gel electrophoresis (PAGE) analysis. The women who were homozygous by radioactive polymerase chain reaction (rPCR) were reanalyzed by methylation-specific polymerase chain reaction (Ms-PCR) and GeneScan analysis. The techniques were validated and compared to arrive at a correction factor. Among 122 genotypes, 35 repeat variants ranging in size from 16 to 57 were observed. The most common repeat is 30 followed by 29. One in 353 women carried the premutation. No full mutations were observed. Screening populations with low frequency of premutations may not be applicable. Ms-PCR is more suitable for routine screening and clinical testing compared with rPCR-PAGE analysis.
Asunto(s)
Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/genética , Síndrome del Cromosoma X Frágil/diagnóstico , Síndrome del Cromosoma X Frágil/genética , Variación Genética , Reacción en Cadena de la Polimerasa/métodos , Repeticiones de Trinucleótidos/genética , Adolescente , Adulto , Electroforesis en Gel de Poliacrilamida/métodos , Femenino , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/química , Pruebas Genéticas , Humanos , India , Metilación , Adulto JovenRESUMEN
We have determined the molecular basis for Usher syndrome type 1F (USH1F) in two families segregating for this type of syndromic deafness. By fluorescence in situ hybridization, we placed the human homolog of the mouse protocadherin Pcdh15 in the linkage interval defined by the USH1F locus. We determined the genomic structure of this novel protocadherin, and found a single-base deletion in exon 10 in one USH1F family and a nonsense mutation in exon 2 in the second. Consistent with the phenotypes observed in these families, we demonstrated expression of PCDH15 in the retina and cochlea by RT-PCR and immunohistochemistry. This report shows that protocadherins are essential for maintenance of normal retinal and cochlear function.
Asunto(s)
Cadherinas/genética , Sordera/genética , Mutación , Precursores de Proteínas/genética , Adulto , Secuencia de Aminoácidos , Animales , Northern Blotting , Western Blotting , Proteínas Relacionadas con las Cadherinas , Cadherinas/análisis , Cóclea/química , Análisis Mutacional de ADN , Femenino , Feto , Perfilación de la Expresión Génica , Ligamiento Genético , Humanos , Hibridación Fluorescente in Situ , Masculino , Ratones , Datos de Secuencia Molecular , Linaje , Polimorfismo Conformacional Retorcido-Simple , Precursores de Proteínas/análisis , Retina/química , Retina/embriología , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de Aminoácido , SíndromeRESUMEN
Genes causing nonsyndromic autosomal recessive deafness (DFNB12) and deafness associated with retinitis pigmentosa and vestibular dysfunction (USH1D) were previously mapped to overlapping regions of chromosome 10q21-q22. Seven highly consanguineous families segregating nonsyndromic autosomal recessive deafness were analyzed to refine the DFNB12 locus. In a single family, a critical region was defined between D10S1694 and D10S1737, approximately 0.55 cM apart. Eighteen candidate genes in the region were sequenced. Mutations in a novel cadherin-like gene, CDH23, were found both in families with DFNB12 and in families with USH1D. Six missense mutations were found in five families with DFNB12, and two nonsense and two frameshift mutations were found in four families with USH1D. A northern blot analysis of CDH23 showed a 9.5-kb transcript expressed primarily in the retina. CDH23 is also expressed in the cochlea, as is demonstrated by polymerase chain reaction amplification from cochlear cDNA.