Exome sequencing and SDH (A, B) immunohistochemistry of canine Pheochromocytomas

Abstract

Pheochromocytomas (PCs) are tumors originating from the chromaffin cells of the adrenal medulla. In people, there are highly correlated to inherited gene mutations in the succinate dehydrogenase (SDH) pathway; however, to date, little work has been done on the genetic basis of these tumors in animals. Out of the total of 2.203 Gb of canine DNA sequenced, 88.35% of bases mapped to exons and 11.65% mapped to introns. Out of 26 genes of interest containing 404 exons, 278 exons were sequenced 68.81%. Sequencing was considered successful when the average read depth was 3x and the entire exon was covered. Coverage ranged from 30% to 100%. Both SDHA and SDHB had exon mapped 46.6% and 62.5% respectively. Additionally, out of 45 known canine variants, exome technique able to detect 36 variants (80%). We performed SDHA and SDHB immunohistochemistry on 35 canine formalin-fixed, paraffin embedded. Interestingly, we had loss of immunoreactivity for both SDHA and SDHB in four samples, suggesting a mutation in SDHx including SDHA. Out of 35 samples, 6 had immunoreactivity for SDHA and 25 lacked immunoreactivities for SDHB. 29 out of the 35 (82%) may have an SDH family mutation other than SDHA. Exome sequencing and immunohistochemistry are able to predict malignant behavior and likelihood of reduction of PCC/PGLs in humans. This can be used to determine whether there are similar mutations in the pseudo-hypoxic, kinase signaling, and other genes of interest exist in dogs, as well as finding novel genes involved in canine Pheochromocytomas oncogenesis.