Late-onset acid maltase deficiency. Detection of patients and heterozygotes by urinary enzyme assay.

Daily urinary excretion of acid maltase (12.78 +/- 2.10 units/24 hr/mg of creatinine, in 11 normal adults) was significantly decreased in ten patients with late-onset acid maltase deficiency (1.33 +/- 0.16 units/24 hr; P less than .001) and 11 heterozygotes (3.27 +/- 0.62 units/24 hr; P less than .001). Maximal inhibition of urinary acid maltase activity by antibodies against human placental enzyme was 53% in controls, 30% in heterozygotes, and virtually absent in patients. Investigation of pH curves and enzyme inhibition by antibodies confirmed the presence in the kidney of an immunologically distinct "extra" maltase enzyme active at acid pH. Whether acid maltase in normal urine originates in the kidney or cells of the lower urinary tract, the enzyme defect seems to be expressed in these cells in late-onset acid maltase deficiency.