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Jeannie Capone: Discovering MTHFR 677TT in Clinical Practice

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May 4, 2026, 14:28

Jeannie Capone: Discovering MTHFR 677TT in Clinical Practice

Jeannie Capone, Author and Independent Science Writer at The Neurolipid Notebook, shared a post on LinkedIn:

“It started as a way to get better at my job as a psychiatric nurse practitioner.

In 2022, I began using pharmacogenetic testing with my patients — not because it was trendy, but because I wanted to understand why some patients complained of side effects on multiple medications, and others didn’t.

We were taught the basics of medication metabolism in school but it was pretty light-weight information.

Early on, I tested myself.

The report gave me information about my lovely liver (CYP enzymes), my UGTs (metabolizing drugs outside the liver) as well as pharmacodynamic genes like HTR2A and SLC6A4.

But there was a second page with just one test.

That’s when things stopped being abstract.

I found out I carry MTHFR 677TT.

This variant produces an enzyme with approximately 50% reduced activity compared to the normal form.

The enzyme’s job is to convert folate into 5-methyltetrahydrofolate — the form the body actually uses for DNA synthesis, methylation reactions, and homocysteine metabolism.

With two T copies, that conversion is impaired.

The result:

lower circulating folate, higher homocysteine, and a system that depends more heavily on adequate B-vitamin intake to function normally.

I brought it to my doctors expecting context — maybe a plan, maybe even reassurance.

After all, I had read that it is correlated with elevated risk of hypertension, hyperhomocysteinemia, cancer, depression, bipolar and heart disease….”

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