Usher syndrome in four Norwegian counties.

Among 89 probands selected for tapeto-retinal degeneration, 18 (20%) were given the diagnosis of Usher syndrome. Among the relatives of the probands another 10 cases of Usher syndrome were found. The distribution on type diagnoses was: Usher syndrome type I: 14 cases, type II: 10 cases and type III: four cases. The pattern of inheritance was autosomal recessive for 12 families, and the remaining six probands were solitary cases without consanguinity between the parents. There was a high intrafamiliar correlation with respect to hearing function, indicating genetic heterogeneity in Usher syndrome. Obligate heterozygotes did not demonstrate heterozygote manifestation. One man with Usher syndrome type I was psychotic, the remaining 27 did not demonstrate serious psychic disturbances. Atactic gait was not observed, though vestibular response was abolished in three patients with Usher syndrome type I. Three patients with type II and one person with type III had normal vestibular response. The prognosis for visual function was not highly correlated to the type diagnosis or to the age when hemeralopia was first noticed. Visual function was good before 30 years of age and bad in most patients after the age of 50.