Stargardt disease (retinal degeneration) (STGD)

Stargardt disease (STGD) is the most common inherited disease causing visual impairment and blindness in human children and young adults. In the breed Labrador Retriever, a variant in the ABCA4 gene has been identified to be associated with a canine form of the Stargardt disease, causing clinical signs similar to the human disease. The ABCA4 gene encodes for a membrane transporter protein located in the outer segments of rod and cone photoreceptors and plays an important role in the visual cycle. The described variant leads to an increased lipofuscin accumulation in the retinal pigment epithelium (RPE) and to a degeneration of both cone and rod photoreceptors. Therefore, affected dogs are visually impaired under daylight and dimlight conditions. Further symptoms are: focal hypertrophy and hyperplasia in the retinal pigment epithelium, the pupils are dilated under daylight, pupillary light and dazzle reflexes are abnormal while menace responses are present. Typically, the cone cells (responsible for light-adapted responses) are affected prior to the rod cells (responsible for dark-adaption) which stay better preserved even in older affected dogs. In contrast to many other inherited retinal diseases, affected dogs retain some vision throughout lifetime.