Low-count fragile-X subjects in fragile-X-positive pedigrees: A clinical and genetic study of two families

Two fragile-X [fra)X)] pedigrees are described, in each of which one member shows a low count of fra(X)-positive cells. One of these two members has large ears and macroorchidism but normal intelligence; the other has normal intelligence but shows an estimated risk to be a fra(X) carrier >90% using the DNA probe U6.2. These data show that individuals with low-count fra(X) cells should be considered as fra(X)-positive when they belong to a fra(X) pedigree and/or present some clinical features of the Martin-Bell syndrome. More specific tools are needed for the laboratory diagnosis of the fra(X) syndrome.