Understanding the impact of 1q21.1 copy number variant

Abstract

Background1q21.1 Copy Number Variant (CNV) is associated with a highly variable phenotype ranging from congenital anomalies, learning deficits/intellectual disability (ID), to a normal phenotype. Hence, the clinical significance of this CNV can be difficult to evaluate. Here we described the consequences of the 1q21.1 CNV on genome-wide gene expression and function of selected candidate genes within 1q21.1 using cell lines from clinically well described subjects.Methods and ResultsEight subjects from 3 families were included in the study: six with a 1q21.1 deletion and two with a 1q21.1 duplication. High resolution Affymetrix 2.7M array was used to refine the 1q21.1 CNV breakpoints and exclude the presence of secondary CNVs of pathogenic relevance. Whole genome expression profiling, studied in lymphoblast cell lines (LBCs) from 5 subjects, showed enrichment of genes from 1q21.1 in the top 100 genes ranked based on correlation of expression with 1q21.1 copy number. The function of two top genes from 1q21.1, CHD1L/ALC1 and PRKAB2, was studied in detail in LBCs from a deletion and a duplication carrier. CHD1L/ALC1 is an enzyme with a role in chromatin modification and DNA damage response while PRKAB2 is a member of the AMP kinase complex, which senses and maintains systemic and cellular energy balance. The protein levels for CHD1L/ALC1 and PRKAB2 were changed in concordance with their copy number in both LBCs. A defect in chromatin remodeling was documented based on impaired decatenation (chromatid untangling) checkpoint (DCC) in both LBCs. This defect, reproduced by CHD1L/ALC1 siRNA, identifies a new role of CHD1L/ALC1 in DCC. Both LBCs also showed elevated levels of micronuclei following treatment with a Topoisomerase II inhibitor suggesting increased DNA breaks. AMP kinase function, specifically in the deletion containing LBCs, was attenuated.ConclusionOur studies are unique as they show for the first time that the 1q21.1 CNV not only causes changes in the expression of its key integral genes, associated with changes at the protein level, but also results in changes in their known function, in the case of AMPK, and newly identified function such as DCC activation in the case of CHD1L/ALC1. Our results support the use of patient lymphoblasts for dissecting the functional sequelae of genes integral to CNVs in carrier cell lines, ultimately enhancing understanding of biological processes which may contribute to the clinical phenotype.

The genetic variability and commonality of neurodevelopmental disease

“…While deletions and duplications of specific loci may yield drastically different phenotypes, the contradictory observation of both deletions and duplications leading to similar phenotypes is also common. This may be explained by the general sensitivity of certain cellular functions to dosage imbalance, such as that observed for the 1q21.1 region [Harvard et al, 2011]. This model is also supported in an alternative gene context by Auerbach et al [2011], who recently demonstrated that fragile X and tuberous sclerosis mouse models affect the same pathway (glutamate receptor 5) in opposite directions with both disruptions resulting in syndromic autism and ID features.…”

“…The commonalities and differences between duplication and deletion phenotypes may be explained, in part, by the variable dosage sensitivity of the genes contained in the CNV region. To this end, Harvard et al [2011] performed functional analyses on two genes with a strong correlation between expression levels and copy number state. In a cell model the authors observed that one gene (CHD1L) demonstrated a functional deficit under both over-and underexpression conditions, while another gene (PRKAB2) only affected its associated functions in a deletion state.…”

1q21.1 Microduplication expression in adults

“…1,2,[5][6][7][8][9][10][11][12] We also examined primary articles and reviews of CNVs in autism, 13 schizophrenia, 14 mental retardation, 15 and congenital heart disease 16 for references to studies reporting subjects with 1q21.1 duplications. [17][18][19][20] Other citations involving 1q21.1 duplication cases were also assessed.…”

“…3,35 We systematically reviewed 28 primary reports identified and their accompanying supplemental materials to identify unique individuals and abstract as much information as possible on each subject. 1,2,[5][6][7][8][9][10][11][12][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] Any subjects with 1q21.1 duplications that were not 1.0-5.0 Mb (Figure 1) in size were excluded, 12,31 allowing us to include atypical variants that were larger or smaller than the standard duplication classes used in our analyses. We documented the ascertainment criteria, country of origin, authors, and the demographic, clinical, and genotypic characteristics of subjects in different studies, and used these variables to attempt to identify duplicate cases reported in two or more papers.…”

“…Four studies were excluded because the sources of subjects overlapped with those of other reports and/or the origin of cases was not specified. 17,18,32,34 We compiled data for 107 subjects from the remaining 22 studies 1,2,[5][6][7][8][9][10][11][19][20][21][22][23][24][25][26][27][28][29][30]33 for the main analyses in this report.…”