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What is the cause of benign transient hyperphosphatasemia? A study of 35 cases
1Department of Paediatric Biochemistry, Royal Hospital for Sick Children, Edinburgh, U.K.
Insights
Benign transient hyperphosphatasemia in children shows seasonal clustering post-summer, with elevated vitamin D and alkaline phosphatase (EC 3.1.3.1) levels. These findings suggest a link between vitamin D and altered liver/bone isoenzyme activity.
Area of Science:
- Biochemistry
- Pediatrics
- Endocrinology
Background:
- Benign transient hyperphosphatasemia is a pediatric condition characterized by elevated alkaline phosphatase.
- Seasonal variations and potential links to vitamin D have been observed but not fully elucidated.
Purpose of the Study:
- To investigate the seasonal patterns and biochemical characteristics of benign transient hyperphosphatasemia in children.
- To explore the potential role of vitamin D and sialic acid in the etiology of this condition.
Main Methods:
- Studied 35 children with benign transient hyperphosphatasemia, comparing them to age- and season-matched controls.
- Measured plasma 25-hydroxyvitamin D concentrations and alkaline phosphatase (EC 3.1.3.1) isoenzyme activities (liver and bone).
- Analyzed isoenzyme electrophoretic mobility and wheat-germ lectin binding, assessing sialic acid content.
Main Results:
- A significant seasonal clustering of cases was observed following summer months.
- Children with the condition had nearly double the plasma 25-hydroxyvitamin D levels compared to controls.
- Elevated activities of both liver and bone alkaline phosphatase isoenzymes were found, with altered electrophoretic mobility and increased sialic acid content.
Conclusions:
- Vitamin D metabolites may mediate increased alkaline phosphatase synthesis.
- High sialic acid content in alkaline phosphatase isoenzymes likely reduces hepatic clearance, contributing to hyperphosphatasemia.
- The condition may be exacerbated by certain drug effects on the liver in some cases.
Abstract:
In a study of 35 children with benign transient hyperphosphatasemia, I found a marked seasonal clustering of cases after the summer months. Furthermore, plasma 25-hydroxyvitamin D concentrations were almost twice those of controls matched for age and time of year. Many children had evidence of weight loss and one had idiopathic hypercalcemia of infancy. Activities both of liver and bone isoenzymes of alkaline phosphatase (EC 3.1.3.1) in plasma were increased. The liver and (to a lesser extent) bone isoenzymes had enhanced electrophoretic mobility, and both showed increased binding to wheat-germ lectin by affinity electrophoresis. For the liver (and probably also the bone) isoenzyme, these changes were due to an increased content of sialic acid. A possible etiology for the condition is proposed involving (a) increased synthesis of alkaline phosphatase, mediated by vitamin D metabolites, and (b) decreased hepatic clearance caused by the high sialic acid content and exacerbated in some cases by the effects of some drugs on the liver.