SOD1:c.118G>A mutation in the Cimarrón Uruguayo dog: prevalence, drift dynamics, and structural effects

Canine degenerative myelopathy (DM) is associated with a missense mutation in the SOD1 gene (c.118G>A), which results in the E40K amino acid substitution and promotes protein aggregation mechanisms similar to those described in human amyotrophic lateral sclerosis. The present study estimated the frequency of the SOD1:c.118G>A mutation in the Cimarrón Uruguayo dog and evaluated its structural and population implications. A total of 82 dogs were genotyped. The mutant allele was detected at a frequency within the range of common variants (q = 0.177), and genotype distribution did not deviate from Hardy-Weinberg equilibrium. Wright-Fisher simulations showed that stochastic processes alone may substantially influence allele-frequency trajectories over time. Additionally, a high-resolution melting (HRM) assay was optimized and enabled clear discrimination of the three genotypes, supporting its use as a rapid genotyping approach. Sanger sequencing of SOD1 exons 2-5 was performed in a subset of individuals to identify additional coding variants. Sequencing revealed no additional non-synonymous variants, except for a synonymous substitution in exon 4. Structural inspection indicated that the E40K substitution does not alter the local hydrogen-bonding pattern but produces a charge inversion that modifies the electrostatic environment surrounding residues 40 and 91. These findings support the hypothesis that electrostatic alterations in this region may contribute to an increased aggregation propensity of mutant SOD1 and provide new insights into the molecular and population context of this mutation in the Cimarrón Uruguayo breed.