Explorative Investigation on Thyroid Peroxidase and Sodium Iodide Symporter Gene Variants in Down Syndrome

Abstract

Objective: Down syndrome (DS), the most common cause of intellectual disability, is frequently associated with thyroid malfunction. Normal thyroid function is essential for growth, neuronal development as well as cognition. Sodium iodide symporter (NIS) and thyroid peroxidase (TPO) are important enzymes for thyroid and to understand their role in DS, we investigated variants in these two genes in families with DS probands (N=183) and controls (N=222). Methods: Genomic DNA isolated from peripheral blood was analyzed by sequencing for genotyping of target sites. Data obtained was analyzed by population-and family-based statistical methods. SNP-SNP interactions were analyzed by Multifactor dimensionality reduction (MDR) test. Results: Out of twelve, only two (rs4808708 and rs4808709) functional SNPs in NIS and among eleven only one SNP, rs1126799 in TPO were polymorphic. Case-control analysis failed to show any statistically significant difference. Family-based analysis revealed significant over transmission of rs1126799 'C' allele to probands. MDR analysis showed synergistic effect of rs1126799 with both rs4808708 and rs4808709. rs4808708 and rs4808709 showed redundancy amongst themselves. Conclusion: This pioneering association study on TPO and NIS gene variants in DS subjects showed synergistic interaction between the SNPs, in absence of any independent contribution, and together may regulate thyroid hormone metabolism.