Familial hypophosphatemic rickets (familialhypophosphatemic rickets), also known as hypophosphatemic anti-vitamin D rickets, is mainly due to mutations in the PHEX gene located on the X chromosome, resulting in reduced renal tubular reabsorption of phosphorus. The main pathophysiological changes in hypophosphatemic rickets are reduced phosphate reabsorption by the proximal renal tubules and reduced calcium and phosphate absorption by the small intestine. Parathyroid hormone and vitamin D levels are normal. Hypophosphatemic rickets can be divided into two types. In type I, renal synthesis of 1,25-dihydroxyvitamin D3 is reduced, resulting in a decrease in its plasma concentration. In type II, 1,25-dihydroxyvitamin D3 plasma concentration is normal or elevated, while the cellular response to 1,25-dihydroxyvitamin D3 is reduced. 2, Pathogenesis The disease manifests as X-linked dominant inheritance, mainly due to mutations in the PHEX gene located on the X chromosome, resulting in reduced phosphorus reabsorption by the renal tubules. The disease is caused by a decrease in phosphorus reabsorption by the renal tubules. Poor intestinal absorption of calcium and phosphorus, reduced blood phosphorus at 0.65-0.97/m renal tubule mol/L (2-3 mg/dl), calcium-phosphorus product mostly below 30, and bone not easily calcified. Male patients can only pass this disease to girls. Female patients can transmit it to both boys and girls. The number of female patients is higher, but the symptoms are light, and most of them only have low blood phosphorus without obvious rickets skeletal changes. Males have a low incidence, but have more severe symptoms. Occasionally, some cases are autosomal recessive. Some cases are sporadic and there is no family history of the disease. The mode of inheritance is mostly X-linked dominant or incomplete dominant, and some are autosomal dominant or recessive. In about 2/3 of cases, it is X-linked dominant inheritance. Male patients can only pass the causative gene to girls. Female patients can pass it on to both boys and girls with a 50% chance. The number of female patients is higher, but the symptoms are mild, and most have only low blood phosphorus without significant rickets skeletal changes. Males have a low incidence, but have more severe symptoms. In non-rickets relatives of patients, this may manifest as hypophosphatasia and reduced renal reabsorption of phosphorus. The other l/3 are sporadic and may be due to de novo mutations, with a mutation rate of 6.4X10-6 in males and 5.3X10-6 in females. occasional cases are autosomal dominant/recessive. A small number of cases are sporadic and have no family history of the disease.