Direct DNA analysis of fragile X syndrome in Spanish pedigrees

Eleven complete Spanish pedigrees with fragile X syndrome were analysed by Southern blotting with the DNA probe StB12.3 previously isolated and described by Oberlé et al. [1991]. This probe allowed the direct detection of affected males and carrier females and was able to distinguish between normal males and normal transmitting males (NTMs). One hundred and twenty three individuals were analyzed, 115 from the pedigrees and 8 from the general population. Five mosaic cases were found (4 males and one female) showing both the premutation and the full mutation. One half of the females with the full mutation were mentally retarded but no female with mental retardation carried the premutated pattern, suggesting that the absence of the full mutation in females is a very good criterion for pre-or postnatal diagnosis of normal mental status.