A boy with Ph1-positive chronic granulocytic leukemia and coincidental active ulcerative colitis presented with high leukocyte alkaline phosphatase (LAP) scores. Recession of the inflammatory process was accompanied by a marked fall of enzyme activity to expected levels for chronic granulocytic leukemia.

The extreme variations of LAP under these and related circumstances appear inconsistent with a simple gene-dose hypothesis as applied to the partial deletion of chromosome 21.

A system of control based on studies of bacterial enzyme synthesis and involving sequential repression by a pair of regulatory genes on chromosome 21 is proposed. Loss of a regulator (modifier) rather than the structural gene for LAP is offered as being in closer accord with the known behavior of this enzyme in chronic granulocytic leukemia.

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© 1965 by American Society of Hematology, Inc.
1965
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