Linkage analysis of the fragile X syndrome using a new DNA marker U6.2 defining locus DXS304

A new RFLP marker U6.2 defining the locus DXS304 was recently mapped to the distal long arm of the X chromosome. In the present study we report the results of genetic linkage analysis of 13 fragile X [fra(X)] families that were informative for the new marker. Analysis of the recombinants for F9-FRAXA, DXS105-FRAXA, DXS98-FRAXA, DXS52-FRAXA, DXS15-FRAXA, and F8C-FRAXA, places DXS304 distal and near to the FRAXA locus. Combined with results from previous studies, our results support the order Xcen.-F9-DXS105-DXS98-FRAXA-DXS304-DXS52-DXS15-F8C-Xqter. Close linkage was observed between DXS304 and the disease locus with a peak lod score of 5.12 at Θ = 0.04 from the present study and, with a peak lod score of 17.45 at Θ = 0.035 when our data are combined with published data from 2 other studies. The present study confirms that U6.2 is useful for prenatal diagnosis and carrier testing in families affected by fra(X) syndrome.