Aspartylglycosaminuria is a classical lysosomal storage disorder caused by defective activity of the lysosomal hydrolase aspartylglucosaminidase. First presentation is usually between two and four years of age, such young patients often suffering from prolonged upper respiratory infections. Developmental of both motor and cognitive skills lags steadily behind that of normal children, and at the puberty AGU patients are mildly or moderately mentally retarded. With increasing age overall performance further declines; the life span of severely retarded individuals is 45 to 50 years.