Familial hypophosphatemic rickets (familialhypophosphatemic rickets), also called hypophosphatemic anti-vitamin D rickets, is mainly due to a mutation in the PHEX gene located on the X chromosome, resulting in reduced renal tubular reabsorption of phosphorus. Poor intestinal absorption of calcium and phosphorus, reduced blood phosphorus, generally between 0.65-0.97/mmol/L (2-3 mg/dl), calcium-phosphorus product mostly below 30, and bone not easily calcified. The mode of inheritance is sex-linked dominant, and it does not respond to general physiological doses of vitamin D. Therefore, it is also called anti-vitamin D rickets and sex-linked hypophosphatemia. I. Examination The main biochemical abnormality seen in the laboratory is hypophosphorus, but the relationship between different sexes, ages and serum should be noted. Blood phosphorus was mostly around 0.65 mmol/L (2 mg/dl), blood calcium values were normal or slightly decreased, serum alkaline phosphatase activity was increased, and urinary phosphorus excretion was increased despite the presence of hypophosphatemia, indicating impaired phosphorus reabsorption by the renal tubules. Amino aciduria, glucosuria, phosphate and potassium have never been found. It has been found that even with impaired renal tubular phosphorus reabsorption, serum phosphorus concentrations may be normal during the first months of life because the glomerular filtration rate is quite low. So the earliest laboratory abnormality may be an increase in serum alkaline phosphatase activity. Urine routine and renal function are normal, and the rate of renal tubular reabsorption of phosphorus is reduced. Second, the auxiliary examination X-ray bone film can see mild and severe rickets changes, active and recovery lesions at the same time, in the femur and tibia are most easily detected. There is backward bone age, knee valgus or inversion. The epiphysis is widened and fragmented, with coarse trabeculae. Cup-shaped changes can be seen in the proximal and distal tibia, as well as in the femur, radius, and distal ulna epiphysis.