ANÁLISE DA ORIGEM PARENTAL DA VARIAÇÃO NO NÚMERO DE CÓPIAS de novo PATOGÊNICAS EM PACIENTES COM DEFICIÊNCIA INTELECTUAL

Abstract

Copy Number Variation (CNV) has been associated with intelectual disability (ID) and this condition occur in approximately 2% of world population. Chromosomal Microarray Analysis (CMA) is being indicated as first-tier test for individuals with ID and has also helped to understand the mechanisms of CNV formation, classification of these rearrangements, type of recurrence, and its origin. The aim of this study was to infer the parental chromosome origin of de novo pathogenic CNV in patients with ID and their mechanisms of formation. Patients with clinical indications of ID were referred to Replicon Research Group/LaGene for G-band karyotyping. CMA approach was done for patients without numerical and/or structural rearrangements results in karyotype. After performing CMA and classification of CNVs, the parental origin of pathogenic CNVs was done using Mendelian error check based on SNPs markers available by ChAs software. In addition, the UCSC Genome Browser website was used to detect Low Copy Repeats (LCR) surrounding the CNVs to infer the mechanisms of their formation. In the period from 2013 to 2015 was performed G-band karyotyping in 290 patients with clinical indication of ID and a total of 193/290 (66.5%) were diagnosed by Karyotype. The group of patients who were not diagnosed using the karyotype, only 76/97 (78.3%) agreed to continue the investigation by CMA’s approach. After performing CMA, a total of 15 de novo pathogenic CNVs were observed, 10 CNV of loss and 5 CNV of gain, in 13/76 (17.1%) patients. The analysis of the parental origin showed 60% of CNVs are of maternal origin and 40% of paternal origin. It was not possible to detect the influence of parental age in the formation of CNVs. After analyzing the presence of surrounding LCRs, it was observed that 46.7% are recurrent CNVs and the mechanism of formation was Non- Allelic Homologous Recombination (NAHR), and 71.4% of these recurrent CNVs are of maternal origin. These data are in agreement with studies that affirm that the majority of CNVs of paternal origin are nonrecurrent due to germ cells replicate many times their genetic material in the pre-meiotic phase, being possible to infer the mechanism of formation of CNV that may have been by Microhomology-mediated break-induced replication (MMBIR) or Non-homologous end joining (NHEJ).