Appaloosa blindness, Leopard complex spotting, LP

 

Gene: TRPM1

Transmission:

Autosomal dominant for spots

For an autosomal dominant genetic disease, an animal must have at least one copy of the mutation in question to be at risk of developing the disease.  Animals with two copies of the mutation generally have more severe symptoms and an earlier onset of the disease than animals with just one copy of the mutation.  One or both of the parents of an animal with the mutation has one or two copies of the mutation.  Animals that have one or two copies of the mutation can pass the mutation on to future generations.

Autosomal recessive for vision problems

For an autosomal recessive genetic disease, an animal must have two copies of the mutation in question to be at risk of developing the disease.  Both parents of an affected animal must be carriers of at least one copy of the mutation.  Animals that have only one copy of the mutation are not at risk of developing the disease, but are carrier animals that can pass the mutation on to future generations.

Mutation: Insertion, TRPM1 gene; retrovirus in intron1

Medical system: Ocular, dermis

Breeds: Appaloosa

Age of onset of symptoms: In juvenile animals for spots, in newborns for vision problems.

Leopard pattern spotting is a spotted pattern of coloration seen in Appaloosa horses.  The pattern and degree of spots can show considerable variation.  Heterozygous animals, with one gene copy mutated, tend to have larger spots, while homozygous mutated animals, with both copies of the gene mutated, tend to have smaller spots.  Leopard Complex refers to a variable combination of leopard spotting, striped hooves, white sclera of the eye, and mottled or speckled skin around the eyes, lips and genitals.  Double mutant animals can have poor vision in dim light (congenital stationary night blindness or Appalooosa blindness) due to a developmental retinal defect.  Vision problems are present at birth and are non progressive.

 

References:

OMIA link: [2139-9796]

Derks MFL, Steensma M. (2021) Review: Balancing selection for deleterious alleles in livestock. Front Genet 12:761728, 2021. [pubmed/34925454]

Druml T, Grilz-Seger G, Neuditschko M, et al. (2017) Phenotypic and Genetic Analysis of the Leopard Complex Spotting in Noriker Horses. J Hered. 108(5):505-514. [pubmed/28453651]

Holl HM, Brooks SA, Archer S, et al. (2016) Variant in the RFWD3 Gene Associated With PATN1, a Modifier of Leopard Complex Spotting.  Anim Genet. 47(1):91-101. [pubmed/26568529]

Scott ML, John EE, Bellone RR, et al. (2016) Redundant Contribution of a Transient Receptor Potential Cation Channel Member 1 Exon 11 Single Nucleotide Polymorphism to Equine Congenital Stationary Night Blindness. BMC Vet Res. 12(1):121. [pubmed/27329127]

Ludwig A, Reissmann M, Benecke N, Bellone R. (2015) Twenty-five thousand years of fluctuating selection on leopard complex spotting and congenital night blindness in horses. Philos Trans R Soc Lond B Biol Sci. 370(1660):20130386. [pubmed/25487337]

Bellone RR, Holl H, Setaluri V, Devi S, et al. (2013) Evidence for a retroviral insertion in TRPM1 as the cause of congenital stationary night blindness and Leopard Complex Spotting in the horse. Plos One 8(10), e78280. [pubmed/24167615]