A recessive lethal chondrodysplasia in a miniature zebu family results from an insertion affecting the chondroitin sulfat domain of aggrecan

Evaluation of a new variant in the aggrecan gene potentially associated with chondrodysplastic dwarfism in Miniature horses

Chondrodysplastic dwarfism in Miniature horses is an autosomal recessive disorder previously associated with four mutations (D1, D2, D3*, and D4) in the aggrecan (ACAN) gene. The aim of this study was to identify additional variants in the candidate ACAN gene associated with chondrodysplastic dwarfism in Miniature horses. Fifteen dwarf Miniature horses were found to possess only one of the dwarfism-causing variants, and two possessed none of the variants. The ACAN exons (EquCab3.0) of seven dwarf Miniature horses were sequenced. A missense SNP in coding exon 11 (g.95271115A > T, c.6465A > T-RefSeq XM_005602799.2), which resulted in the amino acid substitution p.Leu2155Phe (RefSeq XP_005602856.2), was initially associated with the dwarf phenotype. The variant was tested and found present in 14 dwarf foals as well as one parent of each, and both parents of a dwarf possessing two copies. Genetic testing of 347 phenotypically normal Miniature horses demonstrated that none had more than one of the dwarf alleles or c.6465A > T. However, a study of large breeds revealed the presence of c.6465A > T, which was present in homozygosis in two Mangalarga Marchador horses. We suggest that c.6465A > T as a marker of disequilibrium or complex interactions in the Miniature horse genome could contribute to the associated dwarfism.

A structural UGDH variant associated with standard Munchkin cats

Background

Munchkin cats were founded on a naturally occurring mutation segregating into long-legged and short-legged types. Short-legged cats showed disproportionate dwarfism (chondrodysplasia) in which all four legs are short and are referred as standard Munchkin cats. Long-legged animals are referred as non-standard Munchkin cats. A previous study using genome-wide single nucleotide polymorphisms (SNPs) for genome-wide association analysis identified a significantly associated region at 168–184 Mb on feline chromosome (FCA) B1.

Results

In this study, we validated the critical region on FCA B1 using a case-control study with 89 cats and 14 FCA B1-SNPs. A structural variant within UGDH (NC_018726.2:g.173294289_173297592delins108, Felis catus 8.0, equivalent to NC_018726.3:g.174882895_174886198delins108, Felis catus 9.0) on FCA B1 was perfectly associated with the phenotype of short-legged standard Munchkin cats.

Conclusion

This UGDH structural variant very likely causes the chondrodysplastic (standard) phenotype in Munchkin cats. The lack of homozygous mutant phenotypes and reduced litter sizes in standard Munchkin cats suggest an autosomal recessive lethal trait in the homozygote state. We propose an autosomal dominant mode of inheritance for the chondrodysplastic condition in Munchkin cats.

Hanoverian F/W-line contributes to segregation of Warmblood fragile foal syndrome type 1 variant PLOD1:c.2032G>A in Warmblood horses

BACKGROUND

Warmblood fragile foal syndrome (WFFS) is a lethal condition detected in Warmblood horses. Its origin and association with performance traits and fertility among horse populations is unknown.

OBJECTIVES

To validate the previously identified WFFS type 1 (WFFST1)-associated missense variant PLOD1:c.2032G>A and to investigate its distribution among various horses with particular focus on Hanoverian breed, as well as its pathomorphological picture. The study aimed at identifying the origin of the mutant allele and its correlation with performance and fertility traits in Warmblood horses.

STUDY DESIGN

Retrospective case-control and association study.

METHODS

WFFST1 variant was validated using whole genome sequencing (WGS) in 78 equids. In an affected foal with a homozygous mutant genotype, necropsy was performed. Skin samples were examined using histology and transmission electron microscopy. Pathway analysis was performed to trace back 81 genetic carriers to the most common recent ancestor. Furthermore, generalised linear model analysis was employed to test estimated breeding values (EBVs) for differences in performance and fertility traits among different genotypes in Hanoverian horses.

RESULTS

WFFST1 variant had the lowest minor allele frequency among all variants detected in WGS data in the region of PLOD1. Further genotyping of this variant revealed allele frequencies of 0.14 in Hanoverian horses. Histological investigations of the WFFST1-affected foal showed loosely arranged collagen fibres in the dermis. Ultrastructurally, multifocal areas with degraded collagen fibrils and fibrillar plaques were detected. Further pathway analysis revealed a stallion from the Hanoverian sire F/W line as the most common recent ancestor of all tested genetic carriers. Furthermore, WFFST1 variant was found to be correlated with EBVs for gait-related traits as well as conformation and dressage.

MAIN LIMITATIONS

Study evaluated carriers and cases only from Europe.

CONCLUSIONS

This study provides a comprehensive evaluation of WFFST1 variant and traces it back to its potential origin.