A survey of fragile X syndrome in a sample from Spanish Basque country

Fragile X syndrome is the most common inherited form of mental retardation. The syndrome is associated with a CGG repeat expansion in the 5'UTR of the first exon of the FMR1 gene. This gene maps to Xq27.3 and coincides with t he cytogenetic fragile site (FRAXA). The present study deals with the preva lence of fragile X syndrome among individuals with mental retardation of un known cause from institutions and special schools from the Spanish Basque C ountry, Results of cytogenetic and molecular studies, performed in a group of 134 unrelated individuals (92 males and 42 females) are presented. The c ytogenetic marker at Xq27.3 was identified in 12 patients. Other chromosoma l abnormalities were found in two cases that this and previous studies conf irmed as Angelman and Prader-Willi syndromes. Two males, in whom the cytoge netic marker was identified, were found negative for FRAXA and FRAXE expans ion at the molecular level. The present study shows that the frequency of t he FRAXA full mutation in individuals of Spanish non-Basque origin is in th e range of other Spanish populations. In the sample of Spanish Basque origi n we have not found cytogenetic FRAXA site expression, and the CGG repeat s ize of FMR1 gene is in the normal range, The significance of these results are discussed.