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Updated: Aug 16, 2026

Colorimetric Assessment of Deiodinase 1 Activity in Human Liver Microsomes Using the Sandell-Kolthoff Reaction
Published on: April 10, 2026
Polymorphisms in type 2 deiodinase are not associated with well-being, neurocognitive functioning, and preference for
Bente C Appelhof1, Robin P Peeters, Wilmar M Wiersinga
1Department of Endocrinology and Metabolism, Academic Medical Center, University of Amsterdam, F5-171, P.O. Box 22700, 1100 DE Amsterdam, The Netherlands.
Introduction:
Some patients on levothyroxine replacement display significant impairment in psychological well-being, compared with sex- and age-matched controls. Levothyroxine-treated patients can be assumed to derive T3 exclusively from deiodination of T4, which, in the central nervous system, is regulated by type II deiodinase (DII).
Objective:
We investigated whether two recently identified polymorphisms in the DII gene (DII-ORFa-Gly3Asp and DII-Thr92Ala) are determinants of well-being and neurocognitive functioning and associated with a preference for replacement with a combination of T3 and T4.
Methods:
Genotypes for both polymorphisms were determined in 141 patients with primary autoimmune hypothyroidism, adequately treated with levothyroxine monotherapy and participating in a randomized clinical trial comparing T4 therapy with T4/T3 combination therapy. Questionnaires on well-being and neurocognitive tests were performed at baseline.
Results:
Allele frequencies in patients with primary hypothyroidism were similar to those of healthy blood bank donors (32.0 vs. 33.9% for DII-ORFa-Gly3Asp and 40.4 vs. 38.8% for DII-Thr92Ala). DII polymorphisms were not associated with measures of well-being, neurocognitive functioning, or preference for combined T4/T3 therapy.
Conclusion:
The DII-ORFa-Gly3Asp and DII-Thr92Ala polymorphisms do not explain differences in well-being, neurocognitive functioning, or appreciation of T4/T3 combination therapy in patients treated for hypothyroidism.
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