[Chromosome subtelomeric analysis by FISH in patients with mental retardation].

Objective: To assess subtelomeric chromosome anomalies in patients with idiopathic mental retardation (MR).

Methods: Subtelomeric screening was performed in 46 patients with undiagnosed mental retardation. The patients were selected based on the following criteria: (1) MR with two or more of the following conditions: dysmorphic features, prenatal growth retardation, postnatal growth abnormalities, a suggestive family history; (2) chromosome karyotype at the level >450 bands being normal; (3) exclusion of other identified genetic or environmental diagnosis. Fluorescence in situ hybridization (FISH) was performed using ToTelVysion DNA probes. Abnormal findings were confirmed by FISH with a specific subtelomeric probes and family studies were carried out to determine its inheritance.

Result: Clinically significant aberrations were detected in two cases with 6q and 2q terminal microdeletion. The deletion in one case was inherited from a similarly affected father. Subtle chromosomal subtelomeric abnormalities occurred with a frequency of 7.6% in children with moderate to severe mental retardation and of 3.0% in the children with mild retardation.

Conclusion: The results suggest that cryptic abnormalities of the ends of chromosomes might represent a significant cause of mental retardation, and screening for subtelomeric rearrangements might be warranted in children with unexplained mental retardation.