THE FRAGILE-X PHENOTYPE IN A MOSAIC MALE WITH A DELETION SHOWING EXPRESSION OF THE FMR1 PROTEIN IN 28-PERCENT OF THE CELLS

The instability of the CGG repeat region of FMR1 is not restricted to the CGG repeat but expands to flanking sequences as well. A mosaic fra gile X male is reported with a deletion of part of the CGG repeat and 30 bp immediately 3' of the repeat, thus confirming the presence of a hotspot for deletions in the CGG region of FMR1. The deletion, detecte d in 28% of his lymphocytes, did not impair the transcription and tran slation of FMR1, suggesting that regulatory elements are not present i n the deleted region. The patient has the characteristic fragile X phe notype and assuming that the mosaic pattern detected in the lymphocyte s reflects the mosaic pattern in brain, 28% expression of FMRP may not be sufficient for normal cognitive functioning. (C) 1995 Wiley-Liss, Inc.