title: A new insight into fragile X syndrome among Basque population.
abstract: The expansion of a trinucleotide repeat [CGG]n located in the FMR1 X-linked gene is the main cause of fragile X syndrome, the most common form of inherited mental retardation. We have analyzed the factors known, to date, to influence the instability of the repeat in 158 normal X chromosomes from the Spanish Basque population. These factors included length of the repeat, AGG interspersion pattern, length of uninterrupted CGG and DXS548-FRAXAC1 markers associated haplotype. Previous investigations on Basques showed an absence of this disorder among mentally retarded individuals that was likely due to a low prevalence of large CGG alleles and the presence of AGG interruptions on them. The present report suggests that, although the frequency of large alleles is low and they do maintain AGG interruptions, different mutational pathways that might lead to fragile X syndrome could be occurring among Basques. These pathways mainly include alleles with internal sequences 9 + 9 + n and 9 + 12 + 9 that show fragile X associated haplotypes. Besides, the lack of the most proximal AGG interruption, proposed recently as a novel factor involved in CGG repeat instability, was highly identified among alleles with long pure CGG tracts, which showed an internal sequence n + 9. The data suggest that, despite the lower incidence of large alleles, the prevalence of potentially unstable alleles among Basques is similar to that of other Caucasian populations and that these alleles could become fragile X chromosomes.
authors.affiliation: Department of Genetics, Physical Anthropology and Animal Physiology, Faculty of Science and Technology, University of the Basque Country, Spain. peolga@yahoo.com
authors.forename: Olga
authors.initials: O
authors.lastname: Peñagarikano
authors.forename: Alberto
authors.initials: A
authors.lastname: Gil
authors.forename: Mercedes
authors.initials: M
authors.lastname: Télez
authors.forename: Begoña
authors.initials: B
authors.lastname: Ortega
authors.forename: Piedad
authors.initials: P
authors.lastname: Flores
authors.forename: Isabel
authors.initials: I
authors.lastname: Veiga
authors.forename: Ana
authors.initials: A
authors.lastname: Peixoto
authors.forename: Begoña
authors.initials: B
authors.lastname: Criado
authors.forename: Isabel
authors.initials: I
authors.lastname: Arrieta
mesh_terms: D005600:Fragile X Syndrome / Q000208:ethnology / Q000235:genetics*; D005787:Gene Frequency / Q000235:genetics; D005819:Genetic Markers / Q000235:genetics; D005820:Genetic Testing; D005828:Genetics, Population; D006239:Haplotypes / Q000235:genetics; D006801:Humans; D008297:Male; D011110:Polymorphism, Genetic; D019680:Trinucleotide Repeat Expansion / Q000235:genetics; D044465:White People / Q000235:genetics
chemical_list: D005819:Genetic Markers