Although clinical presentations are usually similar, differential diagnosis of different types of rickets such as nutritional and VDDR (VDDR1A, VDDR1B, VDDR2A and VDDR2B) can be made by examining serum levels of 25(OH)2D and 1,25(OH)2D, and their responses to treatment (calcium, vitamin D or calcitriol) (Table 1). This evidence concerns the gene CYP27B1 and rickets.