Abstract

Background: Hashimoto's thyroiditis is a multifactorial disease in which different
environmental factors may trigger the already carried genetic susceptibility in affected
individuals. One of the involved theories in the progression of autoimmune disorders is
the impairment of immunomodulatory activities of vitamin D or its receptors. The gene
polymorphism of vitamin D receptor was reported as an associate of numerous
autoimmune diseases including Addison's disease or type I diabetes mellitus. The
association between vitamin D receptor gene (VDR) polymorphisms and risk of
Hashimoto's thyroiditis was not analyzed in our community yet.
Methods: A case-control study was conducted on 182 Hashimoto's thyroiditis patients
visiting the Al-Hussein teaching hospital in Al-Nasiriah city and Al-Sadder medical city in
Al-Najaf in addition to 200 healthy individuals as a control group. Serum vitamin D3, FT3,
FT4, TSH, anti-TG and anti TPO concentrations were determined by
Electrochemiluminescence methods using Cobas e411 from Roche Company. The
genotyping of VDR gene (TaqI and FokI) was achieved by PCR-RFLP method in all
participants.
Results: Dominant homozygous genotype (FF) were significantly higher in the
Hashimoto's thyroiditis patients compared with those of the control group (OR= 2.22;
P=0.0002), while the OR for the heterozygous Ff genotype (0.63; p=0.029) and recessive
homozygous ff genotype were (0.40; p=0.017) suggesting that the individuals carrying
homozygous dominant FF genotype were two times more susceptible for development
of Hashimoto's thyroiditis than individuals carrying the ff or Ff genotypes which were
more protective from disease. In addition, results regarding VDR-TaqI polymorphism
showed that individuals carrying dominant homozygous TT genotype or T allele have
higher risks to develop Hashimoto's thyroiditis (OR= 2.64 and OR=1.78 respectively).
Conclusion: The current study data of VDR gene polymorphisms suggesting that Iraqi
individuals carrying dominant homozygous FF of rs2228570 SNP and dominant
homozygous TT of rs731236 SNP were more susceptible for development of
Hashimoto's thyroiditis while individuals carrying the ff homozygous or Ff heterozygous
of rs2228570 SNP and heterozygous Tt of rs731236 SNP were more protective from
disease. However, such associations were not related to vitamin D status of the studied
Hashimoto's thyroiditis population.