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Haplotype and AGG Interspersion Analysis of the FMR1 Alleles in Croatian Population: no founder effect detected in patients with fragile X syndrome

Several studies suggested that fragile X syndrome (FRAXA), the most common inherited mental retardation, originated from a limitted number of founder chromosomes. The aim of this work was to assess genetic origin of the fragile X syndrome in Croatian population. We performed haplotype analysis of the polymorphic loci DXS548 and FRAXAC1 in 18 unrelated fragile X and 56 control chromosomes. The AGG interspersion pattern of the FMR1 CGG repeat region was analyzed by sequencing. This is the first report on haplotype and AGG-interspersion analysis of the fragile X syndrome gene in Croatian population – the only eastern European population of Slavic origin analyzed so far. Our findings are intriguing, since they show distinct distribution of the DXS548 and FRAXAC1 alleles in our fragile X population compared to other European fragile X populations. The DXS548/FRAXAC1 haplotype 194/154 (7-3), that is commonly abundant among normal population, was found to be the most frequent in our fragile X population as well. The AGG interspersion analysis indicated that AGG loss rather than haplotype may determine FMR1 allele instability. Our results suggest that no common ancestral X chromosome is associated with the fragile X syndrome in Croatian population studied. Further analysis of fragile X origin among other Slavic populations is necessary in order to better define the eastern European distribution of fragile X chromosomes.

CGG rpeats; fragile X syndrome; FRAXA; FMR1; DXS548; FRAXAC1; haplotype; linkage; mental retardation; Croatia

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