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Early detection of infants with hypophosphatemic vitamin D resistant rickets (HDRR)
K Minamitani1, M Minagawa, T Yasuda
1Department of Pediatrics, Chiba University School of Medicine, Japan.
Insights
Early detection of hypophosphatemic vitamin D resistant rickets (HDRR) in infants is possible before physical signs appear. This study shows biochemical abnormalities and radiographic signs can be identified by three months of age.
Area of Science:
- Pediatrics
- Endocrinology
- Genetics
Background:
- Hypophosphatemic vitamin D resistant rickets (HDRR) diagnosis is typically based on physical signs appearing around 12 months.
- The precise timing of hypophosphatemia and radiographic evidence of rickets in infants born to affected mothers is not well-defined.
Observation:
- A prospective study followed three neonates born to mothers with HDRR.
- Biochemical markers of phosphorus wasting (low serum inorganic phosphorus, reduced tubular reabsorption of phosphate) and radiographic signs of rickets were observed by three months of age in most infants.
- One premature infant diagnosed with HDRR at five months showed characteristic hypophosphatemia due to low TmP/GFR.
Findings:
- Infants born to mothers with HDRR can exhibit early biochemical and radiographic signs of rickets before overt physical manifestations.
- Early treatment with 1 alpha-hydroxyvitamin D3 and phosphate supplementation led to rickets healing and normalized growth.
Implications:
- Early detection and intervention for HDRR in at-risk neonates are feasible, potentially preventing long-term skeletal deformities.
- Further research is needed to fully understand the long-term outcomes of early HDRR treatment in infants.
Abstract:
The onset of physical signs in infants with hypophosphatemic vitamin D resistant rickets (HDRR) has generally been considered to be at the age of 12 months, but the time of appearance of hypophosphatemia and rachitic signs on radiographs remains unclear. We report a prospective study in three neonates whose mothers were HDRR. At birth, despite a low maternal serum inorganic phosphorus (Pi) level, the serum Pi level was normal together with a negligible renal Pi leak in one neonate. At age 3 months, their serum Pi levels, percentages of tubular reabsorption of Pi, and renal tubular maximal rates of Pi reabsorption in relation to the glomerular filtration rate were low except for one infant. Radiographically, their rickets were not apparent at birth but at age 3 months in all. A premature born infant, born at 28 weeks' gestation weighing 1240 g, was diagnosed as HDRR based on hypophosphatemia due to low renal tubular maximal rate of phosphorus reabsorption in relation to the glomerular filtration rate (TmP/GFR) and normal urine Ca excretion at age 5 months. They were initially treated with 1 alpha-hydroxyvitamin D3 (1 alpha OHD3) and later with 1 alpha OHD3 in combination with Pi, which results in healing of the rickets and a normal increase in height. Thus, early detection and treatment of patients born from mothers with HDRR before physical signs of bow-leg and short stature is possible, but the outcome of early treatment requires further study.