Difference in activity properties and subcellular distribution of neutrophil alkaline phosphatase between normal...

Biochemical, cytochemical characteristics and electron microscopy subcellular distribution of neutrophil alkaline phosphatase (NAP) were analysed in blood and/or smear samples from 39 trisomy 21 patients (Down's syndrome) aged 11.5-18 years (mean 15.5 years) and 55 normal subjects aged 12-20.5 years (mean 17 years). All patients were karyotyped. NAP cytochemical procedures were carried out on all subjects; biochemical NAP determinations were made in 10 patients and 20 controls; ultrastructural electron microscopy of AP was performed in three patients and four normal subjects. Neutrophil alkaline phosphatase from patients with trisomy 21 displayed the following changes: (1) a significant increase of enzyme activity, (2) a high thermal lability of enzyme. Electron microscope morphology exhibited large deposits of NAP reaction product associated with the plasma membrane and intracellular main organelles, like phosphasomes. The NAP biochemical and cytochemical characteristics suggest that trisomy 21 neutrophils contain a non-specific AP isoenzyme, closely related to the early placental form.