Studies of Leukocyte Alkaline Phosphatase in Mongolism: a Possible Chromosome Marker.

I N 1959 LEJEUNE, GAUTHIER AND TURPIN’ reported the finding of 47 chromosomes, one more than the normal number, in the cells of children with mongolian idiocy ( Down’s syndrome ) . The extra chromosome, one of the small acrocentrics-prohablv number 21-has since been universally verified. Nowell and Hungerford,2 in 1960, showed that chronic granulocytic leukemia is also associated with an abnormality of a small acrocentric chromosome, probably number 21. The abnormality consists of deletion of a portion of the long arm of one of the pair of chromosomes. Subsequent studies have shown that this disease is almost if not always, accompanied by the chromosome abnormality, and that the abnormality is limited to the blood and bone marrow cells.3 Neutrophilic leukocytes of patients with chronic granulocytic leukemia are strikingly deficient in alkaline phosphatase.4 This observation led to the hypothesis that stimulated the present study; namely, that tile deleted portion of chromosome 21 carried the gene determinant for leukocyte alkaline phosphatase. Trisomy of this chromosome then might lead to increased levels of the enzyme. Preliminary reports from several sources7 9 tend to corroborate this hypothesis.