Analysis of FMR1 and flanking microsatellite markers in normal and fragile X chromosomes in Portugal: evidence for a "protector" haplotype.
In order to look for linkage disequilibrium between the fragile X locus and its flanking markers, we analysed the FRAXAC1 and DXS548 microsatellites in normal and fragile X individuals of Portuguese origin. We observed differences in allele and haplotype frequencies between these two samples. Four haplotypes (A-2, C-2, C-5 and D-6) accounted for 76% of all fragile X chromosomes, whereas a single haplotype (C-7) accounted for 70% of the normal population and less than 3% of the fragile X chromosomes. Among the four observed high-risk haplotypes, A-2 and D-6 had been previously reported in other studies, but C-2 and C-5 seem characteristic of Portuguese patients, as suggested by the high frequency (38%) in fragile X chromosomes and virtual absence in controls. In accordance with previous studies, a greater heterozygosity of the fragile X sample was noted when compared to that of controls. The high frequency of C-7 haplotype in the normal population and its virtual absence in the fragile X sample may reflect the existence of linkage disequilibrium between the two loci and/or selective advantage (protector effect) of this haplotype.
Peixoto
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A
Instituto de Patologia e Imunologia Molecular da Universidade do Porto, Portugal.
dos Santos
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MR
Seruca
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R
Amorim
A
A
Castedo
S
S
D051860:Fragile X Messenger Ribonucleoprotein 1; D005600:Fragile X Syndrome / Q000235:genetics*; D005819:Genetic Markers; D006239:Haplotypes; D006801:Humans; D015810:Linkage Disequilibrium; D008297:Male; D018895:Microsatellite Repeats; D009419:Nerve Tissue Proteins / Q000235:genetics*; D011174:Portugal; D016601:RNA-Binding Proteins
D051860:Fragile X Messenger Ribonucleoprotein 1; D005819:Genetic Markers; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; C497683:FMR1 protein, human