Detection of submicroscopic aberrations in patients with unexplained mental retardation by fluorescence in situ hybridization using multiple subtelomeric probes

Purpose: To further assess the frequency of subtelomeric aberrations in a selected population and to examine the feasibility of a clinical testing. Methods: Patients were selected based on the following criteria: (1) mental retardation (IQ < 70) or developmental delay with dysmorphic features; (2) a normal karyotype at the level of resolution of 450 to 500 bands; and (3) exclusion of other possible etiologies by a full genetic assessment and relevant tests. Fluorescence in situ hybridization (FISH) was performed using multiple subtelomeric probes. Abnormal findings were confirmed by 24-color spectral karyotyping or FISH with a specific subtelomeric probe, and family studies were carried out to determine inheritance. Results: Clinically significant aberrations were detected in 6 of 150 proband patients (4%), while deletion of the 2q subtelomeric region appeared to be a common variant (6%). Conclusions: FISH with multiple subtelomeric probes is a valuable clinical test for establishing a definitive diagnosis for patients with unexplained mental retardation/developmental disorders.