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Extremely low serum pyridoxal 5'-phosphate in children with familial hypophosphatemic rickets
R D Reynolds1, R S Lorenc, E Wieczorek
1Vitamin and Mineral Nutrition Laboratory, Beltsville Human Nutrition Research Center, US Department of Agriculture, MD 20705.
Insights
Children with familial hypophosphatemic rickets (FHR) showed low vitamin B-6 levels, but lacked deficiency symptoms. Serum pyridoxal 5'-phosphate (PLP) is an unreliable indicator for these patients.
Area of Science:
- Biochemistry
- Pediatrics
- Nutritional Science
Background:
- Familial hypophosphatemic rickets (FHR) is a genetic disorder affecting phosphate metabolism.
- Children with FHR often exhibit elevated alkaline phosphatase activity.
- Vitamin B-6 status is typically assessed via serum pyridoxal 5 omino-phosphate (PLP) levels.
Purpose of the Study:
- To evaluate the vitamin B-6 status in children diagnosed with FHR.
- To determine the reliability of serum PLP as a biomarker for vitamin B-6 sufficiency in FHR patients.
- To investigate the clinical relevance of low PLP concentrations in FHR.
Main Methods:
- Assessed serum pyridoxal 5 omino-phosphate (PLP) concentrations in 31 children with FHR.
- Measured alkaline phosphatase activity in all participants.
- Administered pyridoxine hydrochloride (vitamin B-6) to three FHR children and monitored PLP levels and clinical status.
Main Results:
- 15 out of 31 FHR children had undetectable serum PLP levels, the lowest reported.
- The remaining 16 children had very low serum PLP, suggesting potential severe vitamin B-6 deficiency.
- Despite low PLP, none of the children displayed classical vitamin B-6 deficiency symptoms.
- Pyridoxine supplementation transiently increased serum PLP and markedly increased erythrocyte PLP, but did not improve clinical condition.
Conclusions:
- Serum or plasma PLP concentrations are an inappropriate index for assessing vitamin B-6 status in individuals with FHR.
- Elevated alkaline phosphatase activity may interfere with the interpretation of serum PLP levels.
- Further research is needed to establish accurate biomarkers for vitamin B-6 status in FHR and similar conditions.
Abstract:
The apparent vitamin B-6 status of 31 children with familial hypophosphatemic rickets (FHR) was determined. All children had alkaline phosphatase activity that was high-normal to elevated for their ages. A sensitive assay for pyridoxal 5'-phosphate (PLP) indicated that 15 of the 31 children had an undetectable (less than 0.2 nmol/L) concentration of the vitamer--the lowest values yet reported in human serum. The 16 remaining children had concentrations of the vitamer so low that they indicated a potential severe vitamin B-6 deficiency. However, none of the children had ever presented with any of the classical vitamin B-6-deficiency symptoms. Treatment of three additional FHR children with 100 mg pyridoxine.HCl/d resulted in a moderate and transient elevation of their serum PLP concentrations, a dramatic elevation of their erythrocyte PLP concentrations, and no improvement in clinical condition. Serum or plasma PLP concentrations are an inappropriate index for determining vitamin B-6 status in people with FHR and perhaps in others with elevated alkaline phosphatase activity.