Ide Copy Number Variant Does Not Influence Stroke Severity in 2 C57BL/6J Mouse Models nor in Humans: An Exploratory Study.

Abstract

Background: Contrary to the common belief, the most commonly used laboratory C57BL/6J mouse inbred strain presents a distinctive genetic and phenotypic variability, and for several traits, the genotype-phenotype link remains still unknown. Recently, we characterized the most important stroke survival factor such as brain collateral plasticity in 2 brain ischemia C57BL/6J mouse models (bilateral common carotid artery stenosis and middle cerebral artery occlusion) and observed a Mendelian-like fashion of inheritance of the posterior communicating artery (PcomA) patency. Interestingly, a copy number variant (CNV) spanning Ide locus was reported to segregate in an analogous Mendelian-like pattern in the C57BL/6J colonies of the Jackson Laboratory. Given IDE critical role in vascular plasticity, we hypothesized Ide CNV may have explained PcomA variability in C57BL/6J inbred mice.

Methods: We applied a combination of techniques (T2-weighted magnetic resonance imaging, time-of-flight angiography, cerebral blood flow imaging, and histology) to characterize the collaterome in 77 C57BL/6J bilateral common carotid artery stenosis, middle cerebral artery occlusion, naive, and sham mice and performed on these Taqman genotyping, exome sequencing, and RNA sequencing. We then investigated the hypothesis that IDE structural variants (CNVs, gain/loss of function mutations) may have influenced the cerebrovascular phenotype in a large cohort of 454 040 cases and controls (UK Biobank, Genomics England).

Results: We detected an Ide CNV in a bilateral common carotid artery stenosis mouse with 2 patent PcomAs (minor allele frequency, 1.3%), not segregating with the PcomA patency phenotype. In addition, 2 heterozygous IDE CNVs, resulting in loss of function were found in 1 patient with hereditary ataxia, a patient with hereditary congenital heart disease, and 2 healthy individuals (minor allele frequency 9×10^-6). Moreover, we report 4 IDE loss of function point mutations (p.Leu5X, p.Met394ValfsX29, p.Pro14SerfsX26, p.Leu889X, minor allele frequency 0.02%) present also in controls or inherited from healthy parents.

Conclusions: Ide CNV and loss of function variants are rare, do not crucially influence PcomA variability in C57BL/6J inbred mice, and do not cause a vascular phenotype in humans.