The disorder is caused by an inherited autosomal recessive genetic defect. The PRA4 mutation is specific to Lhasa Apso. Two copies of the defective gene (one from each parent) have to be present for a dog to be affected by the disease.
Affected dogs will have normal vision at birth. Disease progression results in complete blindness.
There is a DNA test available; dogs are classified according to three categories.
CLEAR: These dogs have two copies of the normal gene and will not develop PRA as a result of the PRA4 mutation we are testing for.
CARRIER: These dogs have one copy of the mutation and one normal copy of DNA. These dogs will not develop PRA themselves but they will pass the mutation on to approximately 50% of their offspring.
AFFECTED: These dogs have two copies of the PRA4 mutation and will almost certainly develop PRA during their lifetime.