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.