The genetics behind dwarfism in Miniature horses
Miniature horses are selected on their small size. It is known that size in horses is affected by many genes. Unfortunately the small size can also occur because of genetic variants that cause dwarfism.
Dwarfism not only decreases the size but can also be associated with health issues and disproportionate body parts. Dwarf phenotypes in miniature horses range from abnormal abortuses to viable offspring with evidence of skeletal dysplasia. It appears to be a recessive genetic trait, since affected offspring are born out of normal parents. Earlier studies pinpointed the aggrecan (ACAN) gene to cause dwarfism in horses. The aim of this study was to unravel the nucleotide variations in the ACAN gene that cause dwarfism in miniature horses.
The study was executed by comparing the DNA sequences of dwarf and non-dwarf horses. A genome‐wide association study implicated a region of ECA1 with dwarfism in Miniature horses. ACAN was a candidate gene in that region.
Sequencing led to the discovery of four exons possibly associated with dwarfism, where homozygotes and compound heterozygotes always expressed the dwarfism phenotype. However, eight additional horses with dwarfism were found suggesting the existence of additional ACAN alleles causing dwarfism. Among the miniature horses the carrier rate was 26.2% for alleles causing chondrodysplastic dwarfism.
Expert opinion by Anouk van Breukelen
The data of this study provides a foundation for future research of dwarfism in miniature horses as well as other horse breeds.
> From: Eberth et al., Animal Genetics 49 (2018) 413-420. All rights reserved to Stichting International Foundation for Animal Genetics. Click here for the online summary.