Expression of the fragile-X in the "premutated"/"non-imprinted" state

Data about the expression of the fragile site at Xq27.3 from 74 daughters of normal transmitting males (NTMs) were collected from 7 different genetic centers. The majority (85.1%) of these obligate female carriers did not show any cytogenetic expression of fra-X. The remaining 14.9% of these females had frequencies below 3%. In cases with a frequency below 3% of fra-X, a "premutated"/"non imprinted" state of a female carrier should be considered. The results of this collaborative study are in accordance with data from DNA studies taking the premutation model into account.