Polymorphisms of caprine GnRHR gene and their association with litter size in West African Dwarf goats

Gonadotropin-releasing hormone receptor (GnRHR) gene is considered a candidate gene for litter size due to its critical role in regulating the activities of hypothalamo-pituitary-gonadal axis which synthesizes and releases gonadotropins. This study was designed to identify mutations within the caprine GnRHR gene and investigate their association with litter size at various parities. Polymorphisms scanning and genotyping of GnRHR gene in West African Dwarf (WAD) goats (n = 226) revealed three single nucleotide polymorphisms (SNPs), one mutation (g.-29T > G) was detected within 5'UTR region while two others (g.48G > A and g.209T > G) were identified in exon 1. Mutation at g.209T > G locus resulted in amino acid change from Methionine to Arginine at position 70 on the polypeptide residue. Based on heterozygosity and polymorphism information content (PIC), WAD goat population diversity at the SNP loci was moderate. Strong linkage disequilibrium (LD) (r(2) > 0.98) existed among the detected mutations resulting in three observed haplotypes, two (T-G-T and G-A-G) had cumulative frequency of > 97%. The mutation within 5'UTR region of GnRHR gene (g.-29T > G) is novel, being reported in goats for the first time. Association analysis revealed a significant (p < 0.05) association between allele G at g.-29T > G with higher mean litter size for homozygous (GG) mutant does compared with heterozygotes (GT) or homozygotes (TT), while the relationship between SNPs at the two loci detected in exon 1 and litter size was not significant.