Rickets is a common chronic disease in infancy and early childhood. Most rickets is caused by vitamin D deficiency, however, when a child does not do well with standard vitamin D treatment, we need to consider other causes that can cause rickets. Author: Chen Jiao, Peking University International Hospital Source: Pediatrics in Medicine Rickets is a common chronic disease in infancy and early childhood, caused by abnormal calcium and phosphorus metabolism resulting in incomplete bone mineralization, which may initially manifest as night terrors, excessive sweating, and occipital convexity, followed by the gradual appearance of skeletal developmental problems such as cranial softening, hand and foot bracelets, square skull, and rib cage. In the human body, the regulation of calcium and phosphorus metabolism depends mainly on the action of vitamin D and PTH. Vitamin D can elevate both blood calcium and phosphorus. Subcutaneous stores of 7-dehydrocholesterol are converted to vitamin D3 upon exposure to ultraviolet light and, together with our dietary intake of the vitamin, they are transported to the liver for hydroxylation to 25-OH-VD and later to the kidneys for a second hydroxylation to the most active 1,25-(OH)2VD. PTH, which is mainly secreted by the parathyroid glands, also elevates blood calcium but lowers blood phosphorus. The vast majority of rickets are caused by vitamin D deficiency, also called nutritional rickets. This type of rickets mostly develops between the ages of 6 months and 2 years, and the child has a history of inadequate sun exposure and does not regularly take vitamin D or cod liver oil supplements, so vitamin D deficiency leads to lower blood calcium and phosphorus, which generally stimulates increased PTH secretion. The most important basis for diagnosing nutritional rickets is that vitamin D treatment is effective, and if the biochemical indicators such as blood calcium, blood phosphorus and alkaline phosphatase are back to normal after 1 month of treatment. 1, low blood phosphorus anti-vitamin D rickets is the most common anti-vitamin D rickets, mostly X-linked dominant inheritance, more girls than boys suffer from the disease. The main mechanism is impaired renal tubular reabsorption of phosphorus and a partial defect in the conversion of 25-OH-VD to 1,25-(OH)2VD, resulting in increased urinary phosphorus, decreased blood phosphorus, and incomplete bone mineralization. Children are most often seen at the age of 1 to 2 years with unstable walking or lower extremity curvature. Blood biochemistry shows normal calcium and decreased phosphorus, 24-hour urine electrolytes show increased phosphorus excretion, normal 25-OH-VD levels, and 1,25-(OH)2VD levels may be decreased. Children suspected of this disease can be diagnosed with renal tubular phosphorus reabsorption test and intestinal phosphorus loading test, if the rate of renal tubular phosphorus reabsorption is less than 85% twice, and the treatment is mainly phosphate supplementation and active vitamin D. 2. Vitamin D-dependent rickets is divided into two types, type I is 1a-hydroxylase deficiency causing 1,25-(OH)2VD production is blocked, so the 25-OH-VD level is increased. Type II is a defective 1,25-(OH)2VD receptor that prevents it from functioning well, so both 25-OH-VD and 1,25-(OH)2VD levels are high. Both types of children have an early onset and are unable to stand or walk beyond the age of 1 year, and have severe rickets symptoms, which may be combined with feverless convulsions. The blood biochemistry is significantly lower than normal for both calcium and phosphorus, and children with type I may have high amino aciduria. Treatment relies on active vitamin D, with type II requiring higher doses.