Vitamin D deficiency is common in Hashimoto's thyroiditis, while VDR FokI shows subtype-specific association with gravis disease in Jordan: a case-control study.

BACKGROUND: Vitamin D (VD) plays a crucial role in immune regulation via vitamin D receptor (VDR). VD deficiency and VDR gene polymorphism have been linked to autoimmune thyroid disease (AITD). This study investigated serum VD levels and four key VDR gene polymorphism (ApI, BsmI, FokI, TaqI) in the Jordanian population. METHODS: This case control study involves 116 AITD (17 Graves' disease (GD), 99 Hashimoto's thyroiditis (HT)) patients and 106 healthy controls. Serum VD level, thyroid hormones (TSH, FT3, FT4) and autoantibodies (ATG, TPO, TRAB) were measured using electrochemiluminescence immunoassay. Genotypes for VDR SNPs were performed using PCR-RFLP. RESULTS: Patients with AITD had significantly lower VD levels (23.1 ± 11.7 ng/mL) than controls (29.4 ± 18.6 ng/mL), a deficit driven mainly by HT's subgroup. No correlation was found between VD levels and thyroid autoantibody titers. VDR genotype and allele analysis showed no association with AITD overall; however, FokI was significantly associated with GD specifically (OR = 0.18, (P < 0.001), a finding based on a small subgroup (n = 17) requiring replication. CONCLUSION: VD deficiency may act as a general susceptibility factor in HT, while FokI may confer subtype-specific susceptibility to GD independent of a broader VDR-AITD association.