|| no increased risk of thyroid hormone metabolism problems
|| Slight risk of decreased thyroid hormone metabolism
|| Risk of reduced thyroid hormone metabolism
|?|| (C;C) (C;T) (T;T) ||28|
] A common variation in deiodinase 1 gene DIO1 is associated with the relative levels of free thyroxine and triiodothyronine. (Published 2008) Researchers noted that reduced fT3/fT4 ratios may be significant, since various bodily tissues and organs differ in their level of dependence on fT3 and fT4. They analyzed 18 SNPs of DIO1
, DIO2, and DIO3 and measured thyroid hormone levels in 552 people on L-T4 hormone replacement therapy, and three healthy control groups not on L-T4 therapy (totalling 2513 people). Analysis was adjusted for age and sex.
- Among patients, the _minor_ allele of rs11206244 was associated with reduced fT3:fT4 ratio from 0.193 in Common homozygous to 0.175 in Minor homozygous (-0.18) p for trend = 0.004).
- Among patients, the _major_ allele of rs2235544 was associated with reduced fT3:fT4 ratio (from 0.196 in Minor homozygous to 0.177 in Common homozygous (-.019), p for trend = 0.01).
- The two SNPs rs2235544 and rs11206244, were in linkage disequilibrium (LD) (r2 = 0.41), and rs2235544 was driving the association.
- Polymorphisms of rs2235544 in both cases and controls achieved genome-wide significance for effect on fT3/fT4 ratio(p=3.6x10-13) in the general population, each minor allele increasing the ratio by 0.2SD.
- Polymorphism did not affect TSH levels.
- None of the SNPs in the other deiodinase genes DIO2 DIO3 influenced T3, T4 or TSH serum levels.
- Reverse T3 (rT3) levels were not studied.
- Regardless of the polymorphism of rs2235544, the fT3:fT4 ratio and fT3 levels were consistently and significantly lower in hypothyroid patients on L-T4 therapy than in healthy controls, and patients' mean TSH was also lower than in controls.
[PMID 21563302] A 2012 study "The Relationship of Deiodinase 1 Genotype and Thyroid Function to Lifetime History of Major Depression in Three Independent Populations," researchers "confirmed prior findings that two variants in deiodinase 1 (DIO1), including a variant in the 3’ UTR of DIO1 (rs11206244), were associated with altered free thyroxine (FT4) levels in both White and African American subjects. We also found that rs11206244 genotype was associated with lifetime MD (Major Depression) in White female subjects, in particular those from high-risk cohorts. However, we found no association of current FT4 levels with lifetime MD in either ethnic group. We conclude that genetic variation influencing thyroid function is a risk factor for MD." (Abstract)
[PMID 18815314] Cellular and molecular basis of deiodinase-regulated thyroid hormone signaling. This 2008 review discussed findings from previous research, such as:
- Carriers of the T allele of (rs11206244) exhibited higher rT3/T4 and lower T3/rT3 ratios in serum, suggesting a negative effect of this variant on D1 expression and/or activity.
- In contrast, the G allele of (rs12095080) correlated with lower rT3/T4 and higher T3/rT3 ratios, suggesting increased D1 expression and/or activity of this variant.
- the C allele of rs2235544 was associated with increased D1 function and increased FT3/T4 ratio.