Heterozygotes for ACAN dwarfism alleles in horses have reduced stature.

Homozygous and compound heterozygous Miniature horses for ACAN alleles D1, D2, D3* and D4 exhibit chondrodysplastic dwarfism (OMIA 001271-9796). In a previous study, the carrier rate for these four alleles, combined, was 26.2%. The purpose of this study was to investigate whether carriers of these dwarfism-causing alleles had a shorter withers height than non-carriers. A total of 245 Miniature horses were tested for these four ACAN alleles and also were measured for withers height. Of these horses, 98 were carriers and 147 were non-carriers. A statistically significant difference of 1.43 inches was observed with the carriers being shorter (P = 1.72E - 11). The range of heights for the two groups overlapped, indicating that other factors, including genes, have an impact on withers height. However, the high carrier rate of these dwarfism-causing variants may be due to selection for decreased height.

Multiple alleles of ACAN associated with chondrodysplastic dwarfism in Miniature horses.

Chondrodysplastic dwarfism in Miniature horses appeared to be a recessive genetic trait based on the occurrence of affected offspring by normal parents. Dwarf phenotypes vary and range from abnormal abortuses to viable offspring with evidence of skeletal dysplasia. A genome-wide association study implicated a region of ECA1 with dwarfism in Miniature horses. Aggrecan (ACAN) was a candidate gene in that region, and exons were sequenced to compare DNA sequences for dwarf and non-dwarf horses. Sequencing led to the discovery of variants in exons 2, 6, 7 and 15 associated with dwarfism. The four variants are identified with reference to Ecab 3.0 (GCF_002863925.1) as g.95291270del (rs1095048841), g.95284530C>T (ERP107353), g.95282140C>G (rs1095048823) and g.95257480_95257500del (rs1095048839) and designated here as D1, D2, D3* and D4 respectively. A previous study at another laboratory reported dwarfism associated with homozygosity for D3*. Homozygotes for those variants and compound heterozygotes for any combination of those variants always expressed a dwarfism phenotype. However, eight additional horses with dwarfism were found, seven of which were heterozygotes for D2, D3* or D4, suggesting the existence of additional ACAN alleles causing dwarfism. Among Miniature horses, the combined frequency of D1, D2, D3* and D4 was 0.163, suggesting a carrier rate of 26.2% for alleles causing chondrodysplastic dwarfism.

Partial deletion of the LAMA3 gene is responsible for hereditary junctional epidermolysis bullosa in the American Saddlebred Horse.

Laminin 5 is a heterotrimeric basement membrane protein integral to the structure and function of the dermal-epidermal junction. It consists of three glycoprotein subunits: the alpha3, beta3 and gamma2 chains, which are encoded by the LAMA3, LAMB3 and LAMC2 genes respectively. A mutation in any of these genes results in the condition known as hereditary junctional epidermolysis bullosa (JEB). A 6589-bp deletion spanning exons 24-27 was found in the LAMA3 gene in American Saddlebred foals born with the skin-blistering condition epitheliogenesis imperfecta. The deletion confirms that this autosomal recessive condition in the American Saddlebred Horse can indeed be classified as JEB and corresponds to Herlitz JEB in humans. A diagnostic test was developed and nine of 175 randomly selected American Saddlebred foals from the 2007 foal crop were found to be carriers of the mutation (frequency of 0.026).

Synteny-mapping horse microsatellite markers using a heterohybridoma panel.

A panel of horse-mouse heterohybridoma cells was tested for genetic markers using biochemical and polymerase chain reaction-(PCR-) based tests. Biochemical markers included phosphoglucomutase (PGM), glucose phosphate isomerase (GPI) and 6-phosphogluconate dehydrogenase (PGD). Markers detected using PCR-based tests included microsatellite markers HTG2-15, HMS 1-3, 5-8, VHL20, ECA2 and genes for equine major histocompatibility gene ELA-DRA, tumour necrosis factor alpha (TNFA) and transferrin. The results were analysed for correlation and concordance. Based on the results, five synteny groups were identified, specifically between ELA-DRA, TNFA, HMS5 and HTG5; between HTG3 and HTG13; between HTG4, HTG8 and HMS3; between HTG6 and HMS1; and between HTG7, HTG9 and HMS6. Evidence was also found for synteny between HTG12, HMS7 and ECA2, however, confirmation requires further testing. Cytogenetic evaluation of the cell lines making up the panel indicated that large metacentric chromosomes were preferentially lost or tended to break at the centromere. Consequently, the results from this analysis can be used to identify synteny, but not to exclude synteny.