| Abstract |
Single nucleotide polymorphisms (SNPs) in genes involved in thyroid
hormone metabolism may affect thyroid hormone bioactivity. We investigated
the occurrence and possible effects of SNPs in the deiodinases (D1-D3),
the TSH receptor (TSHR), and the T(3) receptor beta (TR beta) genes. SNPs
were identified in public databases or by sequencing of genomic DNA from
15 randomly selected subjects (30 alleles). Genotypes for the identified
SNPs were determined in 156 healthy blood donors and related to plasma
T(4), free T(4), T(3), rT(3), and TSH levels. Eight SNPs of interest were
identified, four of which had not yet been published. Three are located in
the 3'-untranslated region: D1a-C/T (allele frequencies, C = 66%, T =
34%), D1b-A/G (A = 89.7%, G = 10.3%), and D3-T/G (T = 85.5%, G = 14.2%).
Four are missense SNPs: D2-A/G (Thr92Ala, Thr = 61.2%, Ala = 38.8%),
TSHRa-G/C (Asp36His, Asp = 99.4%, His = 0.6%), TSHRb-C/A (Pro52Thr, Pro =
94.2%, Thr = 5.8%), and TSHRc-C/G (Asp727Glu, Asp = 90.7%, Glu = 9.3%).
One is a silent SNP: TR beta-T/C (T = 96.8%, C = 3.2%). D1a-T was
associated in a dose-dependent manner with a higher plasma rT(3) [CC, 0.29
+/- 0.01; CT, 0.32 +/- 0.01; and TT, 0.34 +/- 0.02 nmol/liter (mean +/-
SE); P = 0.017], a higher plasma rT(3)/T(4) (P = 0.01), and a lower
T(3)/rT(3) (P = 0.003) ratio. The D1b-G allele was associated with lower
plasma rT(3)/T(4) (P = 0.024) and with higher T(3)/rT(3) (P = 0.08)
ratios. TSHRc-G was associated with a lower plasma TSH (CC, 1.38 +/- 0.07,
vs. GC, 1.06 +/- 0.14 mU/liter; P = 0.04), and with lower plasma TSH/free
T(4) (P = 0.06), TSH/T(3) (P = 0.06), and TSH/T(4) (P = 0.08) ratios. No
associations with TSH and iodothyronine levels were found for the other
SNPs. We have analyzed eight SNPs in five thyroid hormone pathway genes
and found significant associations of three SNPs in two genes (D1, TSHR)
with plasma TSH or iodothyronine levels in a normal population. |