Fragile X syndrome in the largest world clustering. I. Genetic epidemiology and founder effect outline.

The FMR1 5' regulation gene region harbors a CGG trinucleotide repeat expansion (CGG-TRE) that causes Fragile X syndrome (FXS) when it expands to more than 200 repetitions. Ricaurte is a small village in southwestern Colombia, with an FXS prevalence of 1 in 38 men and 1 in 100 women (~100 times higher than the worldwide reported prevalence), defining Ricaurte as the largest FXS cluster in the world. In the present study, using next-generation sequencing of whole exome capture, we genotype 55 individuals from Ricaurte (49 with either full mutation or with premutation), four individuals from neighboring villages (with either the full mutation or with the premutation), and one unaffected woman, native of Ricaurte, who did not belong to any of the affected families. With advanced clustering and haplotype reconstruction, we modeled a common haplotype of 33 SNPs spanning 83,567,899 bp and harboring the FMR1 gene. This reconstructed haplotype was found in all the men from Ricaurte who carried the expansion, demonstrating that the genetic conglomerate of FXS in this population is due to a founder effect. The definition of this founder effect and its population outlining will allow a better prediction, follow-up, precise and personalized characterization of epidemiological parameters, better knowledge of the disease's natural history, and confident improvement of the clinical attention, life quality, and health interventions for this community.

Avances genómicos de la última década y su influencia en el enfoque diagnóstico de la discapacidad intelectual / Genomic advances in the last decade and their influence in the diagnosis of intellectual disability

RESUMEN La inteligencia humana es un rasgo poligénico (~1000 genes) con una influencia de cada gen aproximadamente ascendente al 0,1%. Es un atributo indispensable para el desarrollo personal, familiar, social y económico y tiene, además, una relación directamente proporcional al mantenimiento de la salud y a una mayor esperanza de vida. La discapacidad intelectual, consecuentemente, afecta todas estas áreas y constituye un problema de salud pública en varios países de Latinoamérica en los que exhibe una prevalencia mayor al 10%. La etiología de la discapacidad intelectual sea aislada o sindrómica, es genética hasta en un 85% de los casos; se diagnostica mediante las nuevas tecnologías de búsqueda en el genoma, tales como la secuenciación masiva y el análisis cromosómico por micromatrices. El diagnóstico etiológico de la discapacidad intelectual permite la selección de terapias específicas, la determinación del pronóstico y de riesgos de recurrencia familiar e individual.

SUMMARY Human intelligence is a polygenic trait (~1000 genes), with an approximate influence of 0.1% per every individual gen. It is an indispensable attribute for personal, familial, social, and economic development; furthermore, it is directly proportional to health maintenance and a longer life expectancy. Consequently, intellectual disability affects all these areas, and constitutes a public health problem in several Latin American countries where it shows a >10%. In ~85% of the patients, the etiology of intellectual disability, be that isolated or syndromic; it is mostly diagnosed through the new technological search studies of the genome, such as new generation sequencing and/or chromosomal microarray analysis. The clinical and etiological diagnosis of intellectual disability, when duly confirmed, allows the choice of specific treatment modalities, the precise determination of prognosis, and the estimation of individual or familial recurrence risks.