Retinal atrophy, Cone-rod dystrophy 2 (CRD2)

Gene: IQCB1

Transmission: Autosomal recessive

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, IQCB1 gene; c.952 ins.C, p.(S319I fs STOP 12), exon10

Medical system: Ocular

Breeds : American Pit Bull Terrier, American Staffordshire Terrier/Amstaff, Boxer, Staffordshire Bull Terrier

Age at onset of clinical signs: Before one year of age

Retinal atrophy refers to a group of genetic diseases affecting the retina. Early retinal degeneration (CRD2) in American Pit Bull Terriers and American Staffordshire Terriers is a genetic eye disease that first affects the cones (colour receptors), followed by the rods (receptors for dim light). Puppies initially show signs of blindness during the day, but over time they also lose their night vision. The first signs of vision loss appear before one year of age, and the animals become completely blind in adulthood.  Retinal changes can be seen on ophthalmic examination at around 3 to 6 months of age.

References:

OMIA link: [1675-9615]

Donner J, Freyer J, Davison S, et al. (2023) Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs.  PLoS Genet. 19(2):e1010651. [pubmed/36848397]

Genetics Committee of the American College of Veterinary Ophthalmologists. (2021) The Blue Book: Ocular disorders presumed to be inherited in purebred dogs. 13th Edition.  [https://ofa.org/wp-content/uploads/2022/10/ACVO-Blue-Book-2021.pdf]

Downs LM, Scott EM, Cideciyan AV, Iwabe S, et al. (2016) Overlap of Abnormal Photoreceptor Development and Progressive Degeneration in Leber Congenital Amaurosis Caused by NPHP5 Mutation. Hum Mol Genet 25(19):4211-4226. [pubmed/27506978]

Palanova A. (2016) The genetics of inherited retinal disorders in dogs: implications for diagnosis and management.  Vet Med (Auckl). 7:41-51. [pubmed/30050836]

Goldstein O, Mezey JG, Schweitzer PA, et al. (2013) IQCB1 and PDE6B mutations cause similar early onset retinal degenerations in two closely related Terrier dog breeds. Investigative Ophthalmology and Visual Science 54(10):7005-7019. [pubmed/24045995]