A human vitamin D receptor mutation causes rickets and impaired Th1/Th17 responses.

We present a brother and sister with severe rickets, alopecia and highly elevated serum levels of 1,25-dihydroxyvitamin D (1,25-(OH)2D3). Genomic sequencing showed a homozygous point mutation (A133G) in the vitamin D receptor gene, leading to an amino acid change in the DNA binding domain (K45E), which was described previously. Hereditary vitamin D resistant rickets (HVDRR) was diagnosed. Functional studies in skin biopsy fibroblasts confirmed this. 1,25-(OH)2D3 reduced T helper (Th) cell population-specific cytokine expression of interferon γ (Th1), interleukins IL-17A (Th17) and IL-22 (Th17/Th22) in peripheral blood mononuclear cells (PBMCs) from the patient's parents, whereas IL-4 (Th2) levels were higher, reflecting an immunosuppressive condition. None of these factors were regulated by 1,25-(OH)2D3 in PBMCs from the boy. At present, both patients (boy is 23 years of age, girl is 7) have not experienced any major immune-related disorders. Although both children developed alopecia, the girl did so earlier than the boy. The boy showed complete recovery from the rickets at the age of 17 and does not require any vitamin D supplementations to date. In conclusion, we characterized two siblings with HVDRR, due to a mutation in the DNA binding domain of VDR. Despite a defective T cell response to vitamin D, no signs of any inflammatory-related abnormalities were seen, thus questioning an essential role of vitamin D in the immune system. Despite the fact that currently medicine is not required, close monitoring in the future of these patients is warranted for potential recurrence of vitamin D dependence and diagnosis of (chronic) inflammatory-related diseases.

[Updates on rickets and osteomalacia: anti-FGF23 antibody, a new therapeutic approach for hypophosphatemic rickets/osteomalacia].

In the last decade, Fibroblast growth factor (FGF) 23 has been shown to be a causative factor of hypophosphatemic rickets/osteomalacia, and considered as potential therapeutic target for this disease. Now the most attention is paid to FGF23 blockades as a new category of therapy that may replace the current supplementation of phosphate and active vitamin D. In this chapter, pharmacological actions of the FGF23-neutralizing antibodies in murine hypophosphatemic rickets/osteomalacia model are reviewed. In addition, other types of FGF23 blockades are also briefly discussed.