Don't forget that processing tryptophan into serotonin is done via a methylation pathway - and indeed there appears to be a connection between MTHFR and depression. See: https://mthfrgenehealth.com/mthfr-depression/

I would guess that making sure you're getting sufficient methyl donors (choline, betaine) in your diet might help with this.

I wonder if there's a MTHFR / Alzheimer's correlation(?) Should be easy enough use mendelian randomization to do a retrospective. You'd think that a subject's dietary input might overwhelm the signal, but the very worst methylators (about 10% of the population) need the equivalent of nine or ten egg yolks of choline per day. Even though half of that can be betaine (trimethyl glycine), I think the number of people with these SNPs who are also getting sufficient methyl donors is small enough to not introduce much noise. Who eats that many eggs - or pounds of beets?

As a below-ideal (but not worst) methylator, this mention of serotonin is very on-point for me. Thanks!