There have been major advances in the past few years in our understanding of
the X-linked learning disabilities. The most common of these is the
fragile-X syndrome, but the number of other gene defects that are now
recognised to be linked with learning disability is increasing year on year.
We describe one family displaying a rare X-linked abnormality. Repeat
genetic testing was requested for a family member with mild learning
disability when, following chromosomal analysis for her brother, it became
known that he had a genetic defect. The genetic defect 46,Xdup(X) (p22.13
p22.31) was identified. To our knowledge this is the first time this precise
configuration has been demonstrated. We conclude that genetic testing for
individuals with learning disability is worthwhile, even when there may be
only a low index of suspicion.