NO APPARENT INVOLVEMENT OF THE FMR1 GENE IN 5 PATIENTS WITH PHENOTYPIC MANIFESTATIONS OF THE FRAGILE-X-SYNDROME

Most fragile X patients have a significant increase in the number of C GG repeats in the FMR1 gene. Two patients were described with a deleti on and one patient with a point mutation in the FMR1 gene. We describe 5 patients with a fragile X or Martin-Bell phenotype. Two brothers we re discordant for the region containing the FMR1 gene; if there is a c ommon cause for the mental retardation this is not located in the FMR1 gene. In the other 3 patients the expression of the FMR1 gene was fou nd to be normal and no abnormalities were noted in the FMR1 mRNA. No a mplification was found in the GCC repeat which is associated with the fragile site FRAXE. We conclude that the Martin-Bell phenotype can als o be caused by mutations outside the FMR1 gene. (C) 1994 Wiley-Liss, I nc.