American Journal of Medical Genetics 132A:210–214 (2005) Research Letter AGG Interspersion Patterns in the CGG Repeat of the FMR1 Gene and Linked DXS548/FRAXAC1 Haplotypes in Brazilian Populations To the Editor:

We have recently described in this journal the distri-bution of CGG repeats of the FMR1 gene, the allelic frequencies at DXS548 and FRAXAC1 microsatellite loci, and DXS548/FRAXAC1 haplotype frequencies in African-derived, European-derived, and Amerindian populations from South America [Mingroni-Netto et al., 2002]. The CGG repeat se-quences and AGG interspersion patterns were not available at that time. A number of haplotype studies in affected males with the fragile X syndrome pointed to two main pathways for the origin of the fragile X mutation in European-derived populations. The two most frequent DXS548/FRAXAC1 haplotypes linked to the fragile X mutation have been found to be associated with CGG repeat structures in the general population, which would favor expansions: the haplotype 2-1 (204/158 bp) is associated to lon