Variants in PTPN22 and SMOC2 genes and the risk of thyroid disease in the Jordanian Arab population

Autoimmune thyroid diseases (AITDs) (Hashimoto thyroiditis and Graves' disease) are complex polygenic disorders with multiple genes thought to contribute to the risk of disease. The contribution of these genes differs by different populations. The PTPN22 gene is reported to be associated with multiple autoimmune diseases, but results of association are conflicting in different populations. The SMOC2 gene is reported to be associated with families with autoimmune vitiligo that had other autoimmunities including thyroid disease. The study aims to investigate the association of PTPN22 and SMOC2 single nucleotide polymorphisms with thyroid disease in a cohort of Jordanian patients. We collected blood samples from 204 thyroid patients and 216 normal controls. We used PCR-RFLP to genotype rs2476601 in PTPN22 and rs13208776 in SMOC2 genes. Both of the SNPS did not show significant association with thyroid disease, even after stratification according to subtype of disease (Hashimoto thyroiditis and Graves' disease) or gender. We reanalyzed SMOC2 SNP using a dominant and recessive models and we got marginal significance when using a dominant model with female-only patients (P = 0.052). PTPN22 SNP did not show association with autoimmune thyroid disease in our patient cohort. This may be due to the low frequency of this SNP in the Jordanian population. SMOC2 SNP, on the other hand, may play a role in AITD susceptibility as a dominant polymorphism. Additional samples might be needed to confirm or exclude association of SMOC2 with AITD.