Association between population structure and allele frequencies of the glycogen synthase 1 mutation in the Austrian Noriker draft horse.

This research paper investigates the frequency of a specific genetic mutation known as glycogen synthase 1 (GYS1) in a type of horse called the Austrian Noriker. The idea is to understand how different breeding strategies and horse populations influence the distribution of this mutation, and the researchers found that factors such as coat colour can affect the frequency of the mutation.

Study Overview and Population Sample

• The study’s primary objectives were to calculate the frequency of the GYS1 mutation associated with polysaccharide storage myopathy type 1 in the Austrian Noriker horse and determine how population substructures influence the distribution of this allele (gene variant).
• The research was conducted on a large-scale sample comprising 208 breeding stallions, 309 mares and a complete unselected cohort of offspring from 2014 (1553 foals).

Differing Allele Frequencies and Influential Factors

• The average proportion of GYS1 carriers in the foal cohort was 33%, but the range varied from 15% to 50%, depending on population substructures based on coat colours.
• In the 517 mature breeding horses, the mutation carrier frequency was at 34% but varied significantly from 4% to 62% within genetic substructures.
• This research revealed that various factors affect the occurrence of the GYS1 mutation. These include coat colour; genetic bottlenecks (a drastic reduction in population size and genetic diversity); and mating strategies such as assortative mating (like with like), random mating and rotating mating practices.

Specific Findings Based on Coat Colours

• Horses with a chestnut coat had the highest frequencies of GYS1 carriers: 50% in foals, 54% in mares and 62% in stallions.
• The average level of inbreeding (mating between closely related horses) was 4.10% for homozygous carrier animals (those inherit the same gene variant from each parent), compared to non-carrier horses where the inbreeding coefficient was 3.48%.
• Meanwhile, those with leopard spots bore the lowest frequencies of GYS1 carriers. Frequency was 15% in foals, 17% in mares and 4% in stallions. In this subpopulation, the level of inbreeding decreased from 3.28% in homozygous non-carrier horses to 0.94% in homozygous carriers.

Inference Drawn from the Study

• The study concludes that lineage breeding and defined mating strategies result in genetic substructures, which can significantly affect the frequencies of the GYS1 gene mutation in the Austrian Noriker horse population.