One of the problems of thyroid hormone blood tests is only the thyroid hormone that gets into cells matters! (Even though I posted a recent item about other ways that thyroid hormone might affect our bodies.) So the amount of thyroid hormone in the blood is a measure of how much is potentially available if it can be taken into cells. But it is not a measure of how much makes it into the cells.
Thyroid hormone Transporters Monocarboxylate Transporter 10 (MCT10) and Monocarboxylate Transporter 8 (MCT8) and OATP1C1 all actively transport thyroid hormone across membranes in our bodies. Anything which makes these less than optimally effective could result in some degree of hypothyroidism within cells.
The paper quoted below is simply some more research results from genetic analysis which seeks to identify associations between various genes (actually, SNPs) and thyroid hormone concentrations.
This is not going to suddenly explain everything - rather it is to point out the very detailed work which is taking place. Hopefully, it also helps to support the frequently repeated statement that we are all different. There is a chance that you know you have one or other of the SNPs identified - but to a large extent that is of interest rather than use at present.
Clin Chim Acta. 2013 Aug 23. pii: S0009-8981(13)00327-6. doi: 10.1016/j.cca.2013.08.017. [Epub ahead of print]
Associations between single nucleotide polymorphisms in thyroid hormone transporter genes (MCT8, MCT10 and OATP1C1) and circulating thyroid hormones.
Roef GL, Rietzschel ER, De Meyer T, Bekaert S, De Buyzere ML, Van Daele C, Toye K, Kaufman JM, Taes YE.
Department of Endocrinology, Ghent University Hospital, Belgium. Electronic address: firstname.lastname@example.org.
Thyroid Hormone (TH) action takes place intracellularly; therefore, transport across the plasma membrane by specific TH transporters, such as MCT8, MCT10 and OATP1C1, is necessary. Several single nucleotide polymorphisms (SNPs) in these genes were reported to be associated with TH concentrations; however, results have been inconsistent.
Six SNPs in TH transporter genes (rs5937843-G/T and rs6647476-T/C in MCT8, rs14399-C/A in MCT10, rs10444412-C/T, rs10770704-C/T and rs36010656-C/A in OATP1C1) were genotyped in 2 cohorts; one consisting of 2416 men and women aged 35-55yrs (Asklepios), the other of 941 men aged 25-45yrs (Siblos), using KASPar technology. TSH, FT3, FT4 and total T3 were determined by immuno-electrochemiluminescence in both cohorts; in the second cohort additional determination of total T4 by electrochemiluminescence and of reverse T3 (rT3) and Thyroid Binding Globulin (TBG) by radioimmunoassays was performed.
The first SNP in MCT8 (rs 5937843-G/T) was inversely associated with FT4 concentrations in men but not in women. In Siblos, this SNP showed also negative associations with TT4 and rT3; in men from Asklepios a trend for positive association with TSH was observed. The second SNP in MCT8 (rs6647476-T/C) was negatively associated with FT3 levels in men from the Siblos and the Asklepios cohort. In addition, an inverse association with TT3 levels in men from the Siblos was observed. Rs36010656 (C/A) in OATP1C1 was not in Hardy-Weinberg equilibrium and therefore excluded from further analyses. The other 2 SNPs in OATP1C1 (rs10444412-C/T and rs10770704-C/T) and the SNP in MCT10 (rs14399-C/A) were not related to TH levels in either cohort.
Two SNPs in MCT8 were related to circulating thyroid hormone levels in men but not in women: the rs5937843 polymorphism (G/T) was inversely associated with FT4 levels and the rs6647476 (T/C) polymorphism related negatively to circulating FT3.
Single Nucleotide Polymorphism (SNP), TSH, monocarboxylate transporter 8 and 10, organic anion transporting polypeptide 1C1, thyroid hormone concentrations, thyroid hormone transporters
[PubMed - as supplied by publisher]