title: Distribution of CGG repeats and FRAXAC1/DXS548 alleles in South American populations.
abstract: In order to assess the molecular variability related to fragile X (FMR1 locus), we investigated the distribution of CGG repeats and DXS548/FRAXAC1 haplotypes in normal South American populations of different ethnic backgrounds. Special attention was given to Amerindian Wai-Wai (Northern Brazil) and Ache (Paraguay), as well as to Brazilian isolated communities of African ancestry, the remnants of quilombos. Comparison of samples from quilombos, Amerindians, and the ethnically mixed, but mainly European-derived population of São Paulo revealed that the 30-copy allele of the fragile X gene is the most frequent in all groups. A second peak at 20 repeats was present in the population of São Paulo only, confirming this as a European peculiarity. The distribution of DXS548 and FRAXAC1 alleles led to a high expected heterozygosity in African Brazilians, followed by that observed in the population of São Paulo. Amerindians showed the lowest diversity in CGG repeats and DXS548/FRAXAC1 haplotypes. Some rare alleles, for example, the 148-bp (FRAXAC1) or 200-bp (DXS548) variants, which seem to be almost absent in Europe, occurred in higher frequencies among African Brazilians. This suggests a general trend for higher genetic diversity among Africans; these rarer alleles could be African in origin and would have been lost or possibly were not present in the groups that gave rise to the Europeans.
authors.affiliation: Centro de Estudos do Genoma Humano, Departamento de Biologia, Universidade de São Paulo, São Paulo, Brazil. renetto@ib.usp.br
authors.forename: Regina Célia
authors.initials: RC
authors.lastname: Mingroni-Netto
authors.forename: Claudia B
authors.initials: CB
authors.lastname: Angeli
authors.forename: Maria Teresa B M
authors.initials: MT
authors.lastname: Auricchio
authors.forename: Emygdia R
authors.initials: ER
authors.lastname: Leal-Mesquita
authors.forename: Andrea K C
authors.initials: AK
authors.lastname: Ribeiro-dos-Santos
authors.forename: Iris
authors.initials: I
authors.lastname: Ferrari
authors.forename: Mara H
authors.initials: MH
authors.lastname: Hutz
authors.forename: Francisco M
authors.initials: FM
authors.lastname: Salzano
authors.forename: Kim
authors.initials: K
authors.lastname: Hill
authors.forename: A Magdalena
authors.initials: AM
authors.lastname: Hurtado
authors.forename: Angela M
authors.initials: AM
authors.lastname: Vianna-Morgante
mesh_terms: D000483:Alleles; D044383:Black People / Q000235:genetics; D001938:Brazil / Q000453:epidemiology; D051860:Fragile X Messenger Ribonucleoprotein 1; D005600:Fragile X Syndrome / Q000453:epidemiology / Q000235:genetics; D005787:Gene Frequency; D006239:Haplotypes; D006801:Humans; D007199:Indians, South American / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics*; D010239:Paraguay / Q000453:epidemiology; D016601:RNA-Binding Proteins; D019680:Trinucleotide Repeat Expansion; D044465:White People / Q000235:genetics
chemical_list: D051860:Fragile X Messenger Ribonucleoprotein 1; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; C497683:FMR1 protein, human