Fragile X Disease
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The term “Fragile X” can be used for either of two conditions resulting from trinucleotide repeat expansions at neighboring loci, FRAXA or FRAXE , in the Xq27–28 region; however, FRAXA is by far the more common condition, and only mutations at this locus cause the classical phenotype of “Fragile X syndrome,” those at FRAXE are responsible for a variable, milder phenotype of nonspecific mental impairment. For this reason, many laboratories consider it cost-effective to test only for FRAXA mutations. However, a brief description of PCR techniques for FRAXE testing are also given (see Note 1 ).
