New informative polymorphism at the DXS304 locus, a close distal marker for the fragile X locus

• Published in: Human genetics 1990-02, Vol.84 (3), p.263-266
• Main Authors: Rousseau, F, Vincent, A, Oberlé, I, Mandel, J L
• Format: Article
• Language: English
• Subjects: Blotting, Southern; DNA Probes; Female; fragile sites; Fragile X Syndrome - genetics; Genetic Markers; Humans; loci; Male; Pedigree; Polymorphism, Restriction Fragment Length; Sex Chromosome Aberrations - genetics
• ISSN: 0340-6717; 1432-1203
• DOI: 10.1007/BF00200572

The polymorphic DNA marker DXS304 detected by probe U6.2 has recently been shown to be closer to the fragile X locus than previously available markers. Its usefulness has however been limited by its relatively low heterozygosity. We have isolated, by cosmid cloning, a 67 kilobase region around probe U6.2 and have characterized a new probe (U6.2-20E) that detects BanI and BstEII restriction fragment length polymorphisms (RFLPs). The BanI RFLP has a heterozygosity of 0.49 and is in partial linkage disequilibrium with the previously described polymorphism, with a combined heterozygosity of 0.63. Furthermore, we have found that the U6.2 original probe, which probably detects an insertion-deletion polymorphism, is also informative in BanI digests. Thus, the two informative RFLPs at the DXS304 locus can be conveniently tested in a single hybridization with a single digest. An updated linkage analysis confirms that DXS304 is distal to the fragile X locus. This informative locus can now be used effectively for genetic mapping of the Xq27-q28 region, and for diagnostic applications in fragile X or Hunter syndrome families.