Testing for DIO1 and DIO2 Deiodinase Enzyme Gene Defects

I wrote a blog post about why I ended up requiring T3-Only to get well a little while ago: http://recoveringwitht3.com/blog/why-paul-needed-t3-only-medication-update

I do find it very interesting that someone with the complete set of deiodinase mutations like I have (DIO1 and DIO2 with both copies of each), can have been so well until my late twenties.

I have spoke to thyroid researchers about this and apparently the body does find ways to compensate for the deiodinase defects. Frequently the conversion issues associated with the DIO1 and DIO2 gene defects do not manifest until someone is in their late twenties to early thirties. Sometimes they never appear to cause problems in some people. Geneticists still do not fully understand why there can be these variations between people.

I had no idea at all that I had any problems until my late twenties and, of course, I was taking no thyroid hormones at all until around age thirty.

I was looking through some old photos today for a different reason and it made me think of this. I found an old photo of me around age 25, and it explains to me why I have taken so long to actually test for DIO1 and DIO2. I just discounted conversion issues due to genes, because I had been so well for so long. I was very fit at the time and I had always assumed that a fundamental conversion issue would have appeared very early on. I now know that this is not true and that a conversion issue can occur later in life.

I do suggest those of you who either have a low FT3 or a high rT3 problem (or both) do get DIO1 and DIO2 tested. It can be really insightful - both in terms of just knowing the answer and in terms of guiding treatment.

23andMe raw data contains the information needed to see if there is a DIO1 defect. 

I personally used Regenerus labs to check for the DIO2 gene defect. 

Other companies may provide both results, but you would need to do your own research.

If you get the testing done and have the raw data, the DIO1 is found by searching for: "rs11206244". The normal allele is C. The T allele reduces T4 to T3 conversion, and increases RT3. DIO2 is found by searching for "rs225014". The wildtype (healthy) allele is T. C is the mutation that reduces T4 to T3 conversion.

I discuss the whole issue of the deiodinase defects in my new book, 'The Thyroid Patient's Manual'. I have also added some discussion of this to the 'Updated Edition 2018' of 'Recovering with T3'

I will attach the photo. It does seem a lifetime ago now. It is about the only one I have of me just before I started to get sick.

Best wishes,


(Updated in February 2018)