This indicates that the genetic distance between the Factor IX gene and the fra(X) locus is too great for Factor IX probes to be used alone for carrier detection in the fra(X) syndrome.
This fragile-X syndrome has been shown to be closely linked also to a Taq I restriction fragment length polymorphism detected by a cDNA probe for factor IX, and the latter locus has been mapped to the subtelomeric region Xq26-Xq28 [Camerino, G., Mattei, M. G., Mattei, G. F., Jaye, B.