GERMLINE MOSAICISM AT THE FRAGILE-X LOCUS

We have identified a fragile X syndrome pedigree where the disorder is associated with a molecular deletion. The deletion was present in the DNA of 2 sons but was absent in the mother's somatic cell (lymphocyte ) DNA. The results are consistent with the deletion arising as a postz ygotic event in the mother, who therefore is germinally mosaic. This f inding has important implications for counseling fragile X families wi th deletion mutations. (C) 1995 Wiley-Liss, Inc.