Transient hyperphosphatasemia in a child with autosomal recessive vitamin D dependency

The case of a 4.5-year-old girl with autosomal recessive vitamin D dependency is described. Although she had been effectively treated since one month postpartum with 1 alpha-hydroxycholecalciferol [1 alpha(OH)D3, alfacalcidol], her mean alkaline phosphatase (EC 3.1.3.1) activity in serum increased to 3680 U/L from a stable value [335 (SD 50) U/L; n = 12] within three weeks, then returned to baseline over the ensuing four months. Transient hyperphosphatasemia was diagnosed. Extensive investigation of an isolated episodic increase in alkaline phosphatase activity is as superfluous in the child with adequately treated metabolic bone disease as it is in other healthy and asymptomatic children.