Neutrophil alkaline phosphatase in children with trisomy 21 and their parents.

A comparative study of karyotypes and neutrophil alkaline phosphatase (NAP) was carried out for 70 parents (35 couples) of trisomy 21 children and their 35 trisomy 21 children and for 110 control parents (55 couples) and their normal children. In the trisomy 21 families we found a significant increase in NAP: mother P less than 10-4; father P less than 10-4; children P less than 10-9; the NAP level in affected child is approximately equal to the sum of the NAP levels of the two parents (P = 0.80; sigma2 = 5%). In one parent of a trisomy 21 child, a karyotype anomaly was present.