An improved and simple micro-method of sphingomyelinase assay in leukocytes and urine

A simple one-vial-method was developed for the quantitative determination of sphingomyelinase activity in human leukocytes and urine, using [14C-methyl] sphingomyelin. The measured activities of healthy control persons show a higher scatter in (n=50) urine (1.2 +/- 0.5 nmol/h . ml urine) than in (n=9) leukocytes (2.15 +/- 0.35 nmol/h . mg protein). Long term tests showed that the enzyme activities in urine can best be correlated to the 24-h-creatinine excretion. A distinct loss of enzyme activity was found in dialyzed urine starting at about the third day; this did not occur in undialyzed urine. The method also shows good reproducibility in micro-tests. It is therefore suitable for screening tests (urine of persons suffering from Niemann Pick disease) and for the prenatal diagnosis of sphingomyelinosis. For one out of two children with symptoms of sphingomyelinosis (hepatosplenomegaly, mental retardation, and neurological deterioration) the diagnosis was confirmed by morphological examination of tissues obtained by biopsy. In both cases leukocytes and urine revealed normal sphingomyelinase activity. These biochemical results in conjunction with the clinical and morphological picture were indicative of type C Niemann-Pick disease.