Juvenile hereditary cataracts are an inherited form of cataracts that commonly cause blindness in dogs by clouding the lens of the eye and affecting both eyes symmetrically.
Phenotype: Juvenile hereditary cataract (JHC) affects both eyes symmetrically and has early onset, with cataract formation starting before 1 year of age and progressing to maturity and blindness by 2-3 years of age.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal, JHC = Juvenile hereditary cataract
Breeds appropriate for testing: Boston Terrier, French Bulldog, Staffordshire Bull Terrier
Explanation of Results:
Dogs with N/N genotype do not have the juvenile hereditary cataract mutation and cannot transmit this variant to their offspring. However, cataracts may develop because of other genetic and environmental factors.
Dogs with N/JHC genotype may not develop juvenile hereditary cataracts, but are carriers. They will transmit this juvenile hereditary cataract variant to 50% of their offspring. Matings between two carriers are predicted to produce 25% of puppies at risk for juvenile hereditary cataracts.
Dogs with JHC/JHC genotype may develop juvenile hereditary cataracts, a condition that progresses to blindness.
Cataracts are a common cause of blindness in dogs. Cataracts are defined as the clouding (opacity) of the lens of the eye. The lens focuses light on the retina to enable vision. Cataracts can therefore impair vision and, if progressive, they can lead to total blindness. Cataracts can develop in one eye (unilateral) or both (bilateral) as a result of the normal aging process, underlying diseases, injury, or be caused by a genetic defect (primary hereditary cataracts). Primary hereditary cataracts tend to be of the bilateral type. In dogs, mutations in the HSF4 gene are associated with two different forms of cataracts, Juvenile Hereditary Cataract (JHC) and Hereditary Cataract (HC).
Juvenile Hereditary Cataract (JHC) found in Boston Terriers, Staffordshire Bull Terriers, and French Bulldogs is a recessive disorder (2 copies of the mutation are necessary for cataracts to develop). JHC affects both eyes symmetrically and has early onset, with cataract formation starting before 1 year of age and progressing to maturity and blindness by 2-3 years of age. JHC affects both sexes equally. Mating of two carriers (N/JHC x N/JHC) is predicted to produce 25% of affected pups. JHC is distinct from the late-onset hereditary cataract also found in Boston Terriers and other breeds, the cause of which has not yet been identified.
Owners and breeders can benefit from this test by identifying at an early age which puppies will have the disease and which will not. Littermates that are either carriers (N/JHC) or clear of the mutation (N/N) are better candidates to retain for breeding purposes. Breeders should avoid mating 2 carriers that can produce affected dogs. Veterinarians can benefit from this test by determining if a clinical cataract case in these breeds has a known genetic etiology.
No copies of JHC mutation. Cataracts may however develop because of other genetic and environmental factors.
1 copy of the JHC mutation. Dog is a carrier. If bred to an N/N dog, 50% of offspring are predicted to be JHC carriers.
2 copies of JHC mutation. Dog is affected. If bred, dog will pass on a copy of JHC to all offspring.
Mellersh, C.S., Pettitt, L., Forman, O.P., Vaudin, M., & Barnett, K.C. (2006). Identification of mutations in HSF4 in dogs of three different breeds with hereditary cataracts. Veterinary Ophthalmology,9(5), 369-378. doi: 10.1111/j.1463-5224.2006.00496.x
Mellersh, C.S., Graves, K.T., McLaughlin, B., Ennis, R.B., Pettitt, L., Vaudin, M., Barnett, K.B. (2007). Mutation in HSF4 associated with early but not late-onset hereditary cataract in the Boston Terrier. Journal of Heredity,98(5), 531-533. doi: 10.1093/jhered/esm043
Mellersh, C.S., McLaughlin, B., Ahonen, S., Pettitt, L., Lohi, H., & Barnett, K.C. (2009). Mutation in HSF4 is associated with hereditary cataract in the Australian Shepherd. Veterinary Ophthalmology,12(6), 372–378. doi: 10.1111/j.1463-5224.2009.00735.x