Subtelomeric FISH findings in Turkish patients with idiopathic mental retardation: Subtelomeric rearrangements are the major cause of idiopathic mental retardation (IMR). This study included 67 Turkish children with IMR. Subtelomere fluorescence in situ hybridization (FISH) was used to determine the subtelomeric rearrangements. Submicroscopic subtelomeric deletions were identified in 5 patients, with a detection rate of 7.4%. The deletions involved 5 different subtelomeric regions (1p, 2q, 8p, 9p and 10p). The detection of subtelomeric rearrangements is of great importance in offering genetic counseling and prenatal diagnosis.