helvella - Thyroid Blog: helvella - DIO1, DIO2 & DIO3 Variants

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This blog is intended to help you look up information about genetic variants (primarily Single Nucleotide Polymorphisms - SNPs) that you might have from doing genetic tests. These variants are found on the genes behind the three primary thyroid-specific enzymes - DIO1, DIO2 and DIO3.

These enzymes are critically important for producing and converting thyroid hormones. Any differences could mean that they work differently to the most common forms. In turn, that might produces differences in results thyroid testing, their interpretation, and the appropriate treatments.

Many other genes affect the thyroid and must not be ignored in trying to identify genetic causes of thyroid variations. This document is limited to these three genes.

Note on Names

These genes and are sometimes mistakenly referred to as D101, D102, etc. That is, D and the numbers 101, 102, etc. But the gene name comes from the name of the enzymes - which are deiodinase enzymes. So they are the letters d-i-o followed by a number 1, 2, etc. Letters not numbers.

It is often clearer in lower-case than capital letters - dio2 rather than DIO2. But it is more common to see it in capital letters!

dbSNP Database

The USA’s National Library of Medicine has a database of genetic variants called “dbSNP”.

It describes itself as:

dbSNP

dbSNP contains human single nucleotide variations, microsatellites, and small-scale insertions and deletions along with publication, population frequency, molecular consequence, and genomic and RefSeq mapping information for both common variations and clinical mutations.

You can look up any Single Nucleotide Polymorphism (SNP) and find out much more about it.

However, the amount of information can be overwhelming. There is an option to filter the information.

There are many other sites which offer genetic information about these and other genes. The dbSNP is comprehensive and well maintained and therefore represents a good starting point. Other sites might be easier to understand.

Filters

The following filters are available on the left-hand side. When you are on the dbSNP website, simply click on the name of the filter you wish to apply.

Clinical Significance 
benign

Validation Status 
by-ALFA
by-cluster
by-frequency

Publication 
PubMed Cited
PubMed Linked

Function Class 
inframe deletion
inframe indel
inframe insertion
initiator codon variant
intron
missense
non coding transcript variant
synonymous

Variation Class 
del
delins
ins

Annotation 
somatic

Global MAF 
Custom range...

Variant Details

Even the actual details are complex.

I have looked up all the SNPs reported by 23andme and, I think, Ancestry, and possibly other genetic tests. (These specific SNPs might or might not be tested in any particular version of these tests. If you are thinking about paying for a test in order to get this information, check thoroughly before ordering.)

[i][b]helvella - DIO1, DIO2 & DIO3 Variants[/b]

How to find out more about the DIO1, DIO2 and DIO3 genetic variants.

Last updated 10/02/2025[/i]

Link to blog:

https://helvella.blogspot.com/p/helvella-dio1-dio2-dio3-variants.html

If you find anything incorrect, misleading, typos, links that don’t work, etc., please let me know. Go to my profile and use the contact details there.

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Links to other posts and blog entries

helvella - DIO1, DIO2 & DIO3 Variants

Note on Names

dbSNP Database

Filters

Variant Details

Gene: DIO1

All DIO1 variants:

Gene: DIO2

All DIO2 variants:

Gene: DIO3

All DIO3 variants:

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