Resumo

PINTO, Maximina Rodrigues et al. The use of a new FISH technique in the study of idiopathic mental retardation . Arq Med [online]. 2006, vol.20, n.1-2, pp.19-24. ISSN 2183-2447.

Introduction: Although mental retardation affects 3% of the population, aetiological factors are still unknown in a considerable number of patients - the so called idiopathic mental retardation. In the last few years, submicroscopic subtelomeric rearrangements were recognized as a cause of idiopathic mental retardation in individuals with a normal conventional karyotype. Different techniques have been developed to detect such rearrangements being FISH the most commonly used. Methods: In a group of 50 mentally retarded individuals selected from our Genetics Clinic, FISH studies with subtelomeric probes were used to determine the frequency of these rearrangements in our study group. At the same time it was our aim to determine/confirm the clinical criteria for future selection of patients to be submitted to these studies. Results: Pathological subtelomeric submicroscopic chromosome abnormalities were only detected in two patients (4%). Both patients have dysmorphic features and anomalies as well as a positive family history of mental retardation. One of the patients was moderately retarded and the other one severely affected. Conclusion: The low frequency of subtelomeric rearrangements found may suggest: 1 - Conventional cytogenetics analysis with high resolution banding allows the exclusion of the majority of chromosome abnormalities including some of the subtelomeric ones; 2 - The majority of patients with these rearrangements have associated anomalies; 3- These anomalies do not seem specific enough to establish reliable clinical pre-selection; 4 - Until simple, cheaper and rapid screening methods become available for diagnostic service, the FISH technique for subtelomeric screening should not be used in non-selected mentally retarded patients.

Palavras-chave : FISH (fluorescence in situ hybridization); submicroscopic; subtelomeric; idiopathic mental retardation; high resolution banding.

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