A new PCR assay useful for screening of FRAXE/FMR2 mental impairment amongmales

FRAXE (FMR2) is a fragile site associated with mental impairment located in Xq28, 600 kb distal to FRAXA (FMR1), the fragile X syndrome fragile site. The FRAXE mutation is an expansion of a CCG repeat that results in methylat ion of a nearby CpG island. FRAXE alleles could be divided into four catego ries: normal (6-30 CCG repeats), intermediate (31-60 CCG repeats), premutat ion (61-200 CCG repeats), and full mutation (over 200 repeats). We have dev eloped a non,isotopic polymerase chain reaction (PCR),based assay for the i dentification of FRAXE full mutation alleles among mentally impaired men. I n this novel PCR test for the FRAXE locus, we used three primers to permit an amplification of a 223 bp monomorphic internal control fragment in addit ion to the amplification of a 419 bp (CCG)(16) FRAXE locus band. A linear s eries of 93 male patients referred for FRAXE testing but found to be negati ve for the (CCG)(n) expansion in the FMR2 gene by Southern blotting analysi s were retested by our PCR technique. In addition, we analyzed two positive controls consisting of a FRAXE fully mutated male and one male with a Xq t erminal deletion. The developed PCR test showed accuracy of 100% in the nor mal individuals retested by PCR analysis, as well as in the two positive co ntrol samples Utilized, in which the strategy of multiplex amplification wo rked as expected. Although not suitable for medical diagnosis of fe males a nd mosaics, it constitutes an important strategy for PCR typing and for FRA XE population screening. Hum Mutat 18:157-162, 2001. (C) 2001 Wiley-Liss, I nc.