c.428_451 dup(24bp) imitation of the ARX gene detected in a Turkish family: ARX mutations give rise to both syndromic and nonsyndromic forms of mental retardation (MR). We investigated the most common ARX mutations, c.428_451 dup(24bp) and c.333ins (GCG)(7). in a series of 370 mentally retarded FMRI (CGG)n expansion mutation negative Turkish patients using PCR amplification and high resolution MetaPhor agarose gel electrophoresis. Sequence analysis was also performed for confirmation and discrimination of the mutations. One patient representing non-syndromic X-linked MR showed an abnormal band pattern on agarose gel and sequence analysis of exon 2 of the ARX gene revealed that the patient had the e.428_451 dup(24bp) mutation. When we screened the family members, we found that his sister and mother were also carrier for the same mutation. The proband showed mild MR and subtle clinical findings like dysarthria and lack of fine motor functions. In conclusion, the patients with weak fine motor skills and positive family history for X-linked MR should be screened for the most common ARX gene mutations.