Absence of subtelomeric rearrangements in selected patients with mental retardation as assessed by multiprobe T FISH.

Background: Mental retardation (MR) is a heterogeneous condition that affects 2-3% of the general population and is a public health problem in developing countries. Chromosomal abnormalities are an important cause of MR and subtelomeric rearrangements (STR) have been reported in 4-35% of individuals with idiopathic MR or an unexplained developmental delay, depending on the screening tests and patient selection criteria used. Clinical checklists such as that suggested by de Vries et al. have been used to improve the predictive value of subtelomeric screening.

Findings: Fifteen patients (1-20 years old; five females and ten males) with moderate to severe MR from a genetics outpatient clinic of the Gaffrée and Guinle Teaching Hospital (HUGG) of the Federal University of Rio de Janeiro State (UNIRIO) were screened with Multiprobe T FISH after normal high resolution karyotyping. No subtelomeric rearrangements were detected even though the clinical score of the patients ranged from four to seven.

Conclusion: In developing countries, FISH-based techniques such as Multiprobe T FISH are still expensive. Although Multiprobe T FISH is a good tool for detecting STR, in this study it did not detect STR in patients with unexplained MR/developmental delay even though these patients had a marked chromosomal imbalance. Our findings also show that clinical scores are not reliable predictors of STR.