Assessment of vitamin D receptors in alopecia areata and androgenetic alopecia. Abstract BACKGROUND: Alopecia areata (AA) is a frequent autoimmune disease, the pathogenesis of which is still unknown. Androgenetic alopecia (Androgenetic Alopecia) is a noncicatricial type of patterned hair loss. Expression of vitamin D receptors (VDRs) on keratinocytes is essential for maintenance of normal hair cycle, especially anagen initiation. OBJECTIVE: To assess VDRs in the skin and blood of AA and Androgenetic Alopecia patients, in order to evaluate their possible role in these hair diseases. METHODS: This study recruited 20 patients with AA, 20 patients with Androgenetic Alopecia, and 20 healthy controls. Blood samples and lesional scalp biopsies were taken from all participants for detection of VDR levels. RESULTS: Serum and tissue VDR levels were lower in AA as well as Androgenetic Alopecia patients when compared to controls (P = 0.000). Serum and tissue VDR were positively correlated in each group. Tissue VDR was significantly lower in female patients with AA than males (P = 0.046) although serum and tissue VDR levels were significantly higher in female Androgenetic Alopecia patients than males (P = 0.004). CONCLUSION: This study suggests an important role for VDR in the pathogenesis of AA and Androgenetic Alopecia through documenting lower serum and tissue VDR levels in AA and Androgenetic Alopecia patients in comparison with controls.