RESUMEN
Knobloch syndrome (KS) is an autosomal recessive disorder defined by the occurrence of high myopia, vitreoretinal degeneration with retinal detachment, macular abnormalities and occipital encephalocele. The KS causative gene had been assigned to a 4.3 cM interval at 21q22.3 by linkage analysis of a large consanguineous Brazilian family. We reconstructed the haplotypes of this family with ten additional markers (five were novel) and narrowed the candidate interval to a region of <245 kb, which contains 24 expressed sequence tags, the KIAA0958 gene and the 5' end of the COL18A1 gene. We identified a homozygous mutation at the AG consensus acceptor splice site of COL18A1 intron 1 exclusively among the 12 KS patients, which was not found among 140 control chromosomes. This mutation predicts the creation of a stop codon in exon 4 and therefore the truncation of the alpha1(XVIII) collagen short form, which was expressed in human adult retina. These findings provide evidence that KS is caused by mutations in COL18A1 which, therefore, has a major role in determining the retinal structure as well as in the closure of the neural tube. Therefore, we show for the first time that the absence of a collagen isoform impairs embryonic cell proliferation and/or migration as a primary or secondary effect.
Asunto(s)
Anomalías Múltiples/genética , Inhibidores de la Angiogénesis/genética , Colágeno/genética , Anomalías del Ojo/genética , Defectos del Tubo Neural/genética , Adulto , Alelos , Cromosomas Humanos Par 21 , Embrión de Mamíferos/citología , Embrión de Mamíferos/metabolismo , Femenino , Marcadores Genéticos , Haplotipos , Humanos , Intrones , Masculino , Neoplasias/genética , Neovascularización Patológica , Especificidad de Órganos , Linaje , Mapeo Físico de Cromosoma , Polimorfismo Conformacional Retorcido-Simple , Empalme del ARN , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , SíndromeRESUMEN
We amplified 305bp of the 3'UT region of COL18A1 from 62 healthy chromosomes from Caucasian individuals. SSCP analysis of these PCR products allowed us to identify 3 alleles which were confirmed through sequencing analysis and ASO. The heterozigosity found for this polymorphic region is 74.2%, and mendelian inheritance was demonstrated in 5 two/three generation families. This polymorphism, located in a region relatively devoid of microsatellites, will be very useful for linkage analysis, particularly for narrowing down candidate regions for genes mapped in this area.