Genomic characterization of some Iranian children with idiopathic mental retardation using array comparative genomic hybridization.

BACKGROUND: Mental retardation (MR) has a prevalence of 1‑3% and genetic causes are present in more than 50% of patients. Chromosomal abnormalities are one of the most common genetic causes of MR and are responsible for 4‑28% of mental retardation. However, the smallest loss or gain of material visible by standard cytogenetic is about 4 Mb and for smaller abnormalities, molecular cytogenetic techniques such as array comparative genomic hybridization (array CGH) should be used. It has been shown that 15‑25% of idiopathic MR (IMR) has submicroscopic rearrangements detectable by array CGH. In this project, the genomic abnormalities were investigated in 32 MR patients using this technique. MATERIALS AND METHODS: Patients with IMR with dysmorphism were investigated in this study. Karyotype analysis, fragile X and metabolic tests were first carried out on the patients. The copy number variation was then assessed in a total of 32 patients with normal results for the mentioned tests using whole genome oligo array CGH. Multiple ligation probe amplification was carried out as a confirmation test. RESULTS: In total, 19% of the patients showed genomic abnormalities. This is reduced to 12.5% once the two patients with abnormal karyotypes (upon re‑evaluation) are removed. CONCLUSION: The array CGH technique increased the detection rate of genomic imbalances in our patients by 12.5%. It is an accurate and reliable method for the determination of genomic imbalances in patients with IMR and dysmorphism.

Primed In Situ Labeling Technique for Subtelomeric Rearrangements in 70 Children with Idiopathic Mental Retardation / 华中科技大学学报（医学）（英德文版）

Subtelomeric rearrangements contribute to idiopathic mental retardation (MR),but most children with idiopathic MR do not show any chromosome abnormalities with standard cytogenetic analysis.The primed in situ labeling (PRINS) technique,using an oligonucleotide primer complementary to the telemetric repeat sequences (TTAGGG),can identify chromosome telomeric abnormality (deletion) in idiopathic MR children.In this study,seventy children with idiopathic MR were enrolled and subjected to PRINS.The results showed normal karyotype in all the children,subtelomeric rearrangements (1q del and 4q del) in 2 cases,which was confirmed by fluorescence in situ hybridization (FISH).It was concluded that PRINS is effective for the detection of subtelomeric rearrangements and may become a routine technique for cytogenetical abnormality screening.

Screening of Subtelomeric Rearrangements in 100 Korean Pediatric Patients with Unexplained Mental Retardation and Anomalies Using Subtelomeric FISH (Fluorescence In Situ Hybridization)

Rearrangements of the subtelomeric regions of chromosomes account for a significant proportion of the underlying genetic defects in both idiopathic mental retardation (MR) and multiple congenital anomalies. To detect the rearrangements, a set of subtelomeric fluorescence in situ hybridization (FISH) probes has been developed. The aim of this study was to reveal the frequency of subtelomeric rearrangements in Korean patients with MR or multiple anomalies. We performed a FISH study using a commercially available subtelomeric FISH probes on a series of unrelated Korean pediatric patients with MR or multiple anomalies without identifiable causes. We used a checklist to evaluate the developmental delay and/or MR. Patients who were shown to have chromosome abnormalities, metabolic disorders, or recognizable dysmorphic syndromes by clinical and laboratory findings were excluded. As a result, 100 patients were eligible for the Subtelomeric FISH study, and a total of 29 patients (29%) were suspected to have subtelomeric rearrangements on initial screening by the multiprobe FISH kit. Among theses, confirmatory FISH studies by using single locus-specific FISH probes were performed in 24 patients. One patient (a 10- yr-old girl) was confirmed to have rearrangement, deletion of the telomeric portion of the short arm of chromosome 4 (4p). Her clinical manifestation was compatible with Wolf-Hirschhorn syndrome, which is known to be caused by 4p deletion. The frequency of subtelomeric rearrangements in this study was 1.1% (1/95), lower than those previously reported (0.5-16.3%). We suggest that subtelomeric FISH test is a useful screening tool for patients with idiopathic MR and/or dysmorphism regardless of its false positive value.