Autosomal dominant hypophosphatemic rickets (ADHR) is a rare disorder with isolated renal phosphate wasting, hypophosphatemia [below 2.5 mg/dL (0.8 mmol/L)], and improperly normal 1, 25-dihydroxyvitamin D3 (calcitriol) levels. Phosphate is vital for a wide array of cellular functions, e.g., it serves as a buffer serum and urine, stores energy in the phosphate bonds of ATP, and is required for building nucleic acids (DNA and RNA). Around 300 mg of phosphate per day penetrates and departs bone tissue. The clinical features of this condition vary widely and they include bone pain, enthesopathy, osteomalacia, rickets, craniosynostosis, and tooth abscesses. The symptoms commence during early childhood with mild cases comprising only hypophosphatemia, while severe cases manifest in slow growth and smaller height. Children with hypophosphatemic rickets develop bone anomalies that obstruct movement and lead to bone pain. The most visible abnormalities include bowed legs or knock knees which worsen if not treated. ADHR can be cured through increasing phosphate intake and high doses of vitamin D. With treatment, hypophosphatemia can improve with time by partly offsetting urine losses of phosphate. There are different types of hereditary hypophosphatemic rickets other than autosomal dominant including autosomal recessive and X-linked recessive, the most common being X-linked hypophosphatemic rickets (XLH).
Autosomal dominant hypophosphatemic rickets originates due to mutations in the fibroblast growth factor 23 (FGF23) gene.