Clinical and morphologic features of mucopolysaccharidosis type II in a dog: Naturally occurring model of Hunter syndrome

A 5-year-old male Labrador Retriever had progressive incoordination, visual impairment, and exercise intolerance. Coarse facial features, macrodactyli a, unilateral corneal dystrophy, generalized osteopenia, progressive neurol ogic deterioration, and a positive urine spot test for acid mucopolysacchar ides suggested mucopolysaccharidosis. Intracytoplasmic vacuoles were most p revalent in epithelial cells, endothelial cells, and histiocytes of liver, kidney, thyroid gland, and spleen. Ultrastructural examination disclosed el ectron-lucent floccular to lamellar membrane-bound storage material charact eristic of mucopolysaccharides. Periodic acid-Schiff-positive intracytoplas mic material was identified in multiple neurons in the medulla, pontine nuc leus, cerebellum, and spinal gray matter horns. Biochemical assays identifi ed a deficiency in iduronate-2-sulfatase (IDS) activity in cultured dermal fibroblasts compared with normal dogs. Hair root analysis for IDS showed th at the dam was a carrier of X-linked Hunter syndrome and that a phenotypica lly normal male littermate of the affected dog was normal. This is the firs t report of Hunter syndrome or mucopolysaccharidosis type II in a dog.