Beta-mannosidosis with angiokeratoma corporis diffusum.

Beta-mannosidosis is a lysosomal disorder which is caused by a deficiency of beta-mannosidase. This disorder was first described in goats. Twelve human cases have already been reported. We present the first case in Japan in whom the diagnosis was reached from angiokeratoma corporis diffusum. Futhermore, mental retardation, hearing loss, and renal failure were also detected. Pseudoxanthoma elasticum was also present, but whether it is a complication of beta-mannosidosis or not remains unknown. The activity level of beta-mannosidase in the patient's plasma was only 2% of the normal range, while that in the patient's mother was 40%. We suggest that beta-mannosidosis should be one of the differential diagnoses when lysosomal enzyme disorders are suspected in cases of angiokeratoma corporis diffusum.