A candidate gene association study of cryptorchidism and scrotal hernia using canine and porcine models

Abstract

Cryptorchidism and scrotal hernia, both being sex-limited complex defects, are the most common congenital defects observed in humans, dogs and pigs. It is believed that these two defects are controlled by multiple genes as well as affected by environmental factors. In this thesis, 22 or 14 functional and positional candidate genes, respectively, have been evaluated to identify the possible associations for crytorchidism in Siberian Huskies and scrotal hernia in pigs. In the canine cryptorchidism study, 76 single nucleotide polymorphisms (SNPs) were found and 51 out of 76 were genotyped by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method or directly sequencing in 156 Siberian Huskies. A Sibling-Transmission Disequilibrium Test (sib-TDT) was first applied to the discordant sib sets (n=38), and then to all 156 dogs including 47 families and 15 individuals. Sib-set analyses showed six SNPs distributed in the collagen type II α 1 (COL2A1) gene were significantly associated with cryptorchidism (P < 0.05). Using a sib-TDT analysis on all 156 dogs, SNP rs23389020 in COL2A1 was suggestively significant (P < 0.06), but not significant after permutation tests (n=1000). Neither of the two haplotypes formed by the five SNPs in COL2A1 was significantly associated with cryptorchidism. In the porcine scrotal hernia study, a total of 1,534 pigs were used including a data set of 692 individuals from 298 pig nuclear families and another data set of 340 unaffected and 502 affected male pigs. The SNPs of all candidate genes were analyzed by using PCR and genotyped by using Sequenom MassArrayTM technology. Statistical analyses were performed on the family-trio and the case-control data, respectively. Two genes involved in collagen