According to the OMIM entry, Thyroglobulin is the glycoprotein precursor to the thyroid hormones T3 (triiodothyronine) and T4 (tetraiodothyronine). Dumont et al. (1989) noted that thyroglobulin provides 3 things: a thyroid hormone precursor, storage of iodine, and storage of inactive thyroid hormones.
The gene's polymorphisms have primarily been associated with Thyroid cancer, and with Hashimoto's thyroiditis and Graves' disease subtypes of AITD (Autoimmune thyroid disease or Autoimmune thyroiditis).
[PMID 14657345] This 2003 article titled "Amino acid substitutions in the thyroglobulin gene are associated with susceptibility to human and murine autoimmune thyroid disease" found that within the TG gene, "exon 10-12 SNP cluster and an exon 33 SNP were significantly associated with AITD."