Abstract
Endometriosis is a complex gynecological condition that affects 6–10% of women in their reproductive years and is defined by the presence of endometrial glands and stroma outside the uterus. Twin, family, and genome-wide association (GWA) studies have confirmed a genetic role, yet only a small part of the genetic risk can be explained by SNP variation. Copy number variants (CNVs) account for a greater portion of human genetic variation than SNPs and include more recent mutations of large effect. CNVs, likely to be prominent in conditions with decreased reproductive fitness, have not previously been examined as a genetic contributor to endometriosis. Here we employ a high-density genotyping microarray in a genome-wide survey of CNVs in a case-control population that includes 2,126 surgically confirmed endometriosis cases and 17,974 population controls of European ancestry. We apply stringent quality filters to reduce the false positive rate common to many CNV-detection algorithms from 77.7% to 7.3% without noticeable reduction in the true positive rate. We detected no differences in the CNV landscape between cases and controls on the global level which showed an average of 1.92 CNVs per individual with an average size of 142.3 kb. On the local level we identify 22 CNV-regions at the nominal significance threshold (P<0.05), which is greater than the 8.15 CNV-regions expected based on permutation analysis (P<0.001). Three CNV's passed a genome-wide P-value threshold of 9.3×10−4; a deletion at SGCZ on 8p22 (P = 7.3×10−4, OR = 8.5, Cl = 2.3–31.7), a deletion in MALRD1 on 10p12.31 (P = 5.6×10−4, OR = 14.1, Cl = 2.7–90.9), and a deletion at 11q14.1 (P = 5.7×10−4, OR = 33.8, Cl = 3.3–1651). Two SNPs within the 22 CNVRs show significant genotypic association with endometriosis after adjusting for multiple testing; rs758316 in DPP6 on 7q36.2 (P = 0.0045) and rs4837864 in ASTN2 on 9q33.1 (P = 0.0002). Together, the CNV-loci are detected in 6.9% of affected women compared to 2.1% in the general population.
Highlights
Endometriosis is a gynecological condition that affects 6–10% of all women in their reproductive years and is defined by the presence of attached endometrial glands and stroma outside the uterine cavity [1]
Using CRLMM [21] to read the raw signal intensity data recorded in the OmniExpress idat-files we summarized the Log R Ratio (LRR) and B Allele Frequency (BAF) at each single nucleotide polymorphisms (SNPs) across all samples in the study for Copy number variants (CNVs) analysis [21,22,23]
Outliers were defined as samples with a CNV-count greater than median plus 1.5 times the inter-quartile range (IQR)
Summary
Endometriosis is a gynecological condition that affects 6–10% of all women in their reproductive years and is defined by the presence of attached endometrial glands and stroma outside the uterine cavity [1]. Endometriosis has a high degree of heritability as shown both in family and twin studies [3,4], and genetic factors may account for as much as 51% of the latent liability [4]. Several independent genome-wide association studies (GWAS) have confirmed the involvement of genetic risk factors in endometriosis [5,6,7,8], only a small percentage of the genetic liability can be assigned to the common GWAS loci – largely leaving the genetic effect unexplained. The GWAS design is well suited to evaluate common loci derived from ancestral founder events, but is not suited to detect rare or multiple mutations at a locus [9] one might expect in conditions with decreased reproductive fitness, such as endometriosis. Strategies complementary to SNPbased GWAS are necessary to detect rare and recent genetic risk variants
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