✍ Scribed by Haddad, Luciana A.; Aguiar, Marcos J.B.; Costa, S�lvia S.; Mingroni-Netto, Regina C.; Vianna-Morgante, Angela M.; Pena, S�rgio D.J.
No coin nor oath required. For personal study only.
We used a non-isotopic polymerase chain reaction (PCR) technique for fragile X syndrome diagnosis to screen 256 mentally retarded boys who were selected randomly from special schools. Patients identified as pre- or full-mutation carriers were further investigated by Southern blot analysis with the StB12.3 probe. The PCR-based test identified five boys with the expanded allele and 17 other patients as carriers of either premutated or gray-zone alleles. The full mutation was confirmed in four cases after Southern blotting and a fifth patient carried a normal allele. Of the 17 patients identified with a premutation allele by PCR, one individual was diagnosed as mosaic by Southern blotting, 12 individuals displayed fragments of 2.90 kb or 2.85 kb, and the remaining four individuals showed apparently normal-sized fragments. However, sizing of these 16 alleles by further PCR analysis showed them to be in the gray-zone range (40-60 repeats). Therefore, the frequency of the full mutation in this cohort of mentally retarded boys was close to 2% (5/256). The prevalence of gray-zone alleles among those mentally impaired boys who did not carry the full mutation was 6.4% (16/251) and, although more than twice the prevalence of these alleles among a cohort of unaffected Brazilian males 2.8% (71251), the difference did not reach statistical significance.
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