Intestinal enterokinase deficiency.

Enterokinase is an enzyme secreted by the mucosa of the small intestine and is responsible for the conversion of trypsinogen to its active product, trypsin. Its key role in initiating the formation of proteolytic enzymes from their inactive precursors is illustrated in Fig. 1. When the pancreatic zymogens reach the duodenum, trypsin is formed by the action of enterokinase on trypsinogen and this trypsin then activates the other pancreatic proteolytic zymogens (chymotrypsinogens and pro-carboxypeptidases). Enterokinase was first discovered in 1899 by Schepowalnikov working in Pavlov's laboratory, and because of its enzymic action on another enzyme, Pavlov (1967) aptly described it as a 'ferment of ferments'. Despite considerable interest in the physiology of enterokinase during the earlier part of this century, and the fact that its absence should result in marked impairment of protein digestion, it has not excited much medical interest. We describe 2 children who presented with diarrhoea and failure to thrive, in whom the underlying abnormality was found to be enterokinase deficiency. A brief report of Case 1 has previously appeared as a preliminary communication (Hadorn et al., 1969) and Case 2 has been recorded in abstract form (Tarlow and Hadorn, 1970).