Transient hyperphosphatasemia of infancy and early childhood: clinical and biochemical features of 21 cases and literature review.

Clinical and biochemical features of transient hyperphosphatasemia of infancy and early childhood are reviewed in 21 patients we have studied and in a further 93 cases reported in the literature. The diagnosis is suggested by the finding of an increased activity of alkaline phosphatase (EC 3.1.3.1) in plasma, typically more than fivefold the adult upper reference limit, in a child under five years of age, without evidence of liver or bone disease. The condition is confirmed by the presence of a characteristic pattern of alkaline phosphatase isoenzymes and by the normalization of the enzyme's activity in plasma within approximately three months. The etiology of the condition and possible mechanisms of the enzyme increase are discussed.