In clinical practice, however, patterns often emerge before the research fully catches up. One such pattern I observe is a striking overlap between individuals with MTHFR gene variants and symptoms of ADHD or ADD. To be clear: this is not yet a fully established causal relationship. But there is enough emerging evidence—and strong biochemical plausibility—to warrant a closer look.

Histamine and MTHFR are bound together for so many reasons. Histamine levels are affected by methylation, and histamine breakdown is methylation-dependent. Another big reason is that just like MTHFR, histamine has its fingers in so much more than just allergies.