FISH screening for subtelomeric rearrangements revealed 4 different chromosomal anomalies in 55 children with intellectual deficit

Intellectual deficit affects about 1-3% of the population. The cause of mental retardation is unknown in large number of patients and presents significant diagnostic problem. Data from the literature suggest that a proportion of cases are due to constitutional chromosome aberrations, and some 7% are associated to rearrangements of subtelomeric chromosome regions. We present the results of cytogenetic and FISH study in our sample of 55 children with developmental delay. The aim of this study was to determine the frequency and types of subtle structural rearrangements of subtelomeric regions in our group of patients and review the data reported in literature. The children involved in this study had mild to moderate mental retardation, dysmorphic features, malformations, behavioral anomalies, uncomplicated pregnancy and birth. No cases with familial history of mental retardation were included in this study. The analysis was carried out on slides obtained by peripheral blood culture using high resolution GTG-, RBG- and CBG-banding method and commercially available FISH subtelomere screening tool. For understanding the mechanism of origin of structural rearrangement additional analysis using WCP-, CEP- and LSI-probes were performed. All children had normal karyotype at 450-550 band level. Rearrangements involving subtelomeric regions were detected in 4 (7.2%) out of 55 children. There was one familial case, one de novo rearrangement and in two children the parents were not available for cytogenetic and FISH studies. The investigation disclosed one deletion and three unbalanced translocations. This study confirms that rearrangements of subtelomeric chromosome region are significant cause of developmental delay, and that subtelomeric screening and detection of subtelomeric rearrangements in patients with intellectual deficit is important for carrier identification, genetic counseling and prenatal diagnosis.