Retesting for fragile X syndrome in cytogenetically normal males

This case series describes four males who presented with learning and behavioural difficulties. In each case, the diagnosis of fragile X syndrome was delayed because of an initial false-negative cytogenetic result. Although most children are currently investigated for fragile X syndrome using highly sensitive and specific molecular techniques, there still remain a large number of older children who have been tested using only cytogenetic analysis. The clinical presentation of these four children and the reason for the occurrence of the false-negative results are considered. In addition, there is a discussion and illustration of how a screening checklist can be used to help clinicians to decide which children should be retested.