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We report the case of a healthy young man presenting with atypical neutrophil alkaline phosphatase (NAP) and reduced neutrophil chemotactic activity, but with no susceptibility to infection. NAP activity was low, kinetic parameters were modified and immunoreactive properties and subcellular distribution were abnormal. Neutrophil morphology was normal. A similar pattern was observed in the patient's healthy brother. The profile of the observed anomalies offers some similarity to that previously described in patients with chronic myelogenous leukaemia. However, in the present case, the NAP deficiency with impaired neutrophil function was present in two brothers with no haematological symptoms and is probably related to a non-acquired neutrophil abnormality. This observation of a primary NAP variant reinforces the hypothesis of a direct link between NAP activity and functional properties of neutrophils.

A kinetic parameter (the Vm/Km ratio), an index of neutrophil alkaline phosphatase catalytic efficiency, was studied in 36 women with normal pregnancies at 16-20 weeks' gestation. On each blood sample, determinations were achieved on enzyme extracted from maternal granulocytes by monitoring the phosphohydrolytic activity at 400 nm on a spectrophotometer equipped with software for computation of kinetic parameters. Infant sex was recorded at the delivery for all women included in this study. The recent introduction of NAP as a marker for some pathological pregnancies requires a better knowledge of the behaviour of that enzyme in physiological conditions. Data reported focus attention on fetal sex. It appears to be one of the factors involved in variations of kinetic parameters observed in maternal NAP. Sex-linked differences in placental maturation could explain these results.

Alkaline phosphatase concentrations are known to increase in blood neutrophils of normal pregnant women. The main kinetic parameters of this enzyme were analysed and compared in a group of 30 women with normal pregnancies and a group of 11 women whose fetuses had trisomy 21 (Down's syndrome = DS). The subjects were studied at an identical stage of gestation. Significant changes occurred in thermal stability and urea resistance in cases of DS pregnancies. We also investigated the inactivation constants for two chemicals: L-p-bromotetramisole, an uncompetitive inhibitor, and sodium thiophosphate, a competitive inhibitor. Ki measured for the two inhibitors were found to be significantly lower in cases of pathological pregnancies. The patterns observed in inhibition constants extend the biochemical characteristics of the atypical isoenzyme expressed in neutrophils of women with DS pregnancies.