b -mannosidosis is a very rare disorder with only 10 cases in 7 families being known (Oct 1995). Clinical features vary widely but there has always been mental retardation. There may be some dysmorphism, dysotosis multiplex and angiokeratoma (the latter seen only in two brothers). One case only was particularly severe.
ENZYME TESTS: Deficiency of b -mannosidase is the primary defect.