A new DNA probe of potential use for diagnosis of the fragile-X syndrome.

A new cloned DNA probe (U6.2), which recognizes a TaqI polymorphism near the locus for the fragile-X syndrome, was tested in a great Xq-fra pedigree. In the corresponding four families studied, the probe is informative and no recombinations were observed between the probe and the disease locus, although recombinational events were observed with several other probes tested in the past. The locus defined by the probe, DXS304, cosegregated with the fragile-X phenotype in 20 informative meioses (z = 3.09, theta = 0.00). The degree of polymorphism at this locus and its proximity to the fragile-X locus makes it useful for diagnostic applications.