Screening for subtle chromosomal rearrangements in an Egyptian sample of children with unexplained mental retardation

Mental retardation is present in about 1–3% of individuals in the general population, but it can be explained in about half of the cases. A descriptive study was carried out to screen for subtle chromosomal rearrangements in a group of Egyptian children with idiopathic mental retardation (IMR) to estimate its frequency if detected. The study enrolled 30 patients with IMR, with the perquisite criteria of being <18 years at referral, their IQ <70, and manifesting at least one of the criteria for selection of patients with subtelomeric abnormalities. Males were 63.3% and females were 36.7%, with a mean age of 7.08 ± 4.22 years. Full history taking, thorough clinical examination, IQ, visual, and audiological assessment, brain CT scan, plasma aminogram, pelvi-abdominal ultrasonography, echocardiography, and cytogenetic evaluation using routine conventional karyotyping, high resolution banding (HRB), and fluorescent in situ hybridization (FISH) technique with appropriate probes were carried out for all studied patients.All enrolled patients had apparently normal karyotypes within 450 bands resolution, except for one patient who had 46, XY, [del (18) (p11.2)]. HRB and FISH showed subtle chromosomal rearrangement in 10% of cases that have been proven to be subtelomeric in 2 cases, i.e., 6.8%: 46, XY, dup (17) (p13.3), 46, XY, del (2) (q36.1–36.3), and non-subtelomeric in one case, 5.5%, 46, XX, ins (7;?) (q22;?). To conclude, in children with IMR and clinical phenotype indicative of a suspected chromosomal anomaly, once recognizable syndromes have been excluded, abnormalities that include the ends of chromosomes must be searched for using HRB and subtelomeric FISH even when conventional karyotyping fails to demonstrate any abnormality.