To Explore The Parental-of-origin Of De Novo And Pathogenic Copy Number Variation With Intellectual Disability And Other Congenital Birth Defects

Background:Germ cell is the key to biological reproduction and is the carrier that parent passed the genetic information to offspring. The stability and integrity of its genome is a necessary condition for the faithful transmission of genetic information. And it is also essential For human reproductive health and offspring development. In the course of human germ cells (including germline stem cells in mitosis and meiosis of germ cells), the genome will produce point mutations, microsatellite DNA variation, copy number variation (CNV) and many other variations. These germ cell genomic variations are not only an important source of biodiversity and genetic differences in individual organisms, but also have an important role in the pathogenesis of human diseases.The human genome CNV is a research hot spot of life science in recent years. It’s the main subtype of genome structure variation (SV). CNV refers to the length of more than1kb fragments of DNA copy number increase or decrease, including deletion, duplication, and more complex type of variation. In addition, the SV also includes more classic chromosomal inversion, balanced translocation, and other forms of variations. The newly discovered submicroscopic level of CNV exhibited high mutation rate, a large degree of variation, which covered5-10%of the human genome. These CNVs mainly come from the process of germ cell DNA damage repair, replication errors, homologous recombination, chromosome wrongly separation and many other kinds of ways. It is the important pathogenic factor to mental retardation, neuro-developmental abnormalities, male infertility and other serious diseases. CNV pathogenic mechanisms may include gene dosage effect, gene disruption, gene fusion and location effects. In-depth study of the CNV and its parental origin, allows us to get a better understanding of the human genome’s constitute, the genetic differences between individuals, as well as genetic risk factors occurred during the relative contribution of germ cells in the genome CNV.Objective:By tracing the parental-origin of de novo pathogenic CNVs, eggs and sperm genome stability study relative contribution to reproductive health, and guide the genome related to the differential diagnosis of disease and prenatal diagnosis, prevention of congenital birth defects, mental retardation, etc, and provides the theory basis for human genetic diseases.Methods:Through a retrospective single nucleotide/short tandem repeat transmission of the human genome and other information of genetic markers within the pedigree to determine the de novo pathogenic CNV parental-origin (paternal or maternal),and to explore the relative contribution during process of sperm and egg occurs in CNV of the genome. A sequence homology search using RepeatMasker (http://www. repeatmasker.org/cgi-bin/WEBRepeatMasker) with a100-kb window of sites of CNV (±50kb in either end) was carried out to investigate possible mechanisms of CNV formation.Results:There are23cases with paternal allele loss of heterozygosity and12cases with maternal allele loss of heterozygosity among the deletion cases(paternal numbers/maternal numbers=23/12). And there are3cases with heterologous paternal allele duplication and9cases with heterologous maternal allele duplication among the duplication cases (paternal numbers/maternal numbers=3/9). None of SD flanking sequence has been found that accompanied with the47CNVs by searching homologous sequence with a100-kb window of sites of CNV (±50kb in either end) through RepeatMasker.Conclusions:1. Deletion CNVs have some paternal bias and the relative contribution of spermatogonia in the process of deletion CNVs is larger. Otherwise, heterologous duplication CNVs have significant maternal bias and the relative contribution of oocytes in the process of heterologous repeat CNVs relatively is larger.2. CNVs with heterozygosity deletion can be formed in any of a division process period in the germline. CNVs with heterologous duplication should be formed before the second meiotic division in the germline.3. Non-recurrent CNVs accompanied with no SD flanking sequence suggest that it may not be generated by NAHR mechanism in meiosis, but may be generated by non-homologous end joining (NHEJ) or micro-mediated homologous sequences from DNA break induced replication (MMBIR).