In a man with severe mental retardation, minor facial and genital anomalies, disproportionate short stature and a broad thorax, we identified a de novo Xq13.2q21.1 duplication by array CGH. This 7 Mb duplication encompasses 23 known genes, including the X-linked mental retardation (XLMR) genes ATRX and SLC16A2. The phenotype of this patient is similar to that described in more than 10 previously reported patients with overlapping Xq duplications. Detailed comparison of the clinical characteristics and the function of the genes located in the commonly duplicated regions of these patients led us to the hypothesis that an increased dosage of ATRX and perhaps of other genes is involved in the pathogenetic mechanism of this XLMR phenotype, including mental retardation, short stature, and genital abnormalities comprising cryptorchidism and/or a small penis.