Risk factors for insidious uveitis in the Knabstrupper breed

Kingsley, Nicole B.; Sandmeyer, Lynne S; Parker, Sarah; Dwyer, Ann E.; Heden, Sanna; Reilly, Camilla; Hallendar‐Edman, Anna; Archer, Sheila

doi:10.1111/evj.13879

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“…Variants in TRPM1 and RFWD3 are involved in leopard complex spotting, a group of white spotting patterns that tend to be symmetrical and centered over the hips (Bellone et al, 2013; Holl et al, 2016). Horses homozygous for the 1378 bp insertion in TRPM1 have congenital stationary night blindness and are at risk for insidious uveitis (Bellone et al, 2013; Kingsley et al, 2022; Rockwell et al, 2020; Sandmeyer et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

A de novo 2.3 kb structural variant in MITF explains a novel splashed white phenotype in a Thoroughbred family

Bellone,

Tanaka,

Esdaile

et al. 2023

Animal Genetics

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Splashed white in horses is characterized by extensive white patterning on the legs, face and abdomen and may be accompanied by deafness. To date, seven variants in microphthalmia‐associated transcription factor (MITF) and two variants in Paired Box 3 (PAX3) have been identified to explain this phenotype. A splashed white Thoroughbred stallion, whose sire and dam were not patterned, was hypothesized to have a de novo variant leading to his white coat pattern. A whole‐genome sequencing candidate gene approach identified two single nucleotide variants (SNVs) in SOX10, four SNVs in MITF and a 2.3 kb deletion in MITF with the alternative allele present in this stallion but absent in the other 18 horses analyzed. All six SNVs were annotated as modifiers and were not further considered. The deletion in MITF (NC_009159.3:g.21555811_21558139delinsAAAT) encompasses exon 9 encoding a part of the helix–loop–helix domain required for DNA binding. Sanger sequencing and parentage testing confirmed that this deletion was a de novo mutation of maternal origin. Consistent with the published nomenclature, we denote this likely causal variant as SW8. Genotyping three of this stallion's offspring identified SW8 only in the nearly all‐white foal that was confirmed deaf by brainstem auditory evoked response testing. This foal was also a compound heterozygote for dominant white variants (W20/W22), but to date, W variants alone have not been connected to deafness. SW8 marks the fourth de novo MITF variant in horses reported to cause white patterning. The link between deafness and all MITF variants with and without other variants impacting melanocyte development and function needs to be further explored.

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