[Rickets].

This review mainly describes on childhood vitamin D deficiency and x-linked hypophosphatemic rickets. Though nutritional state has improved dramatically, 25 (OH) D level, which is a good indicator of vitamin D status, is marginal especially in winter, and vitamin D deficiency is not rare in Japan. The PTH/Vitamin D axis does not account for the entire picture of x-linked hypophosphatemic rickets, and a new bone (osteocyte) -renal metabolic milieu has emerged and loss of PHEX, mostly expressed in osteocytes, is proposed to result in inappropriate processing of MEPE and consequent reduction in bone mineralization and an increase in circulating FGF23 to give rise to phosphaturia and hypophosphatemia.