IDENTIFICATION BY STS PCR SCREENING OF A MICRODELETION IN XP21.3-22.1ASSOCIATED WITH NONSPECIFIC MENTAL-RETARDATION

X-linked non-specific mental retardation (MRX) is a heterogeneous cond ition in which mental retardation (MR) appears to be the only consiste nt manifestation. The genetic and phenotypic heterogeneity exclude any possibility of pooling families and, therefore, of fine-mapping the r elated disease genes, In order to identify genomic critical regions in volved in the MRX condition assigned to Xp21.3-22.1 region, we have im plemented the PCR screening of non fragile X MR patients for the prese nce of deletions in this region. The amplification by PCR of 12 marker s located between POLA and DXS704 using genomic DNA from 192 MR males led to the identification, in a 9 year old mentally retarded boy, of a microdeletion which extends from DXS1202 to DXS1065, None of the know n genes, POLA, MAGE genes cluster, DAX1, GK and DMD, that map in the X p21.3-22.1 region is affected by this deletion. This approach, which c ould easily be applied to several other MRX loci, allowed not only a c onfirmation of the presence of a potential locus in Xp21.3-22.1 involv ed in non-specific mental retardation, but also a better definition of the genomic critical region corresponding to this locus.