A large-scale screen for coding variants in SERT/SLC6A4 in autism spectrum disorders.

Takeshi’s team read every letter of the serotonin transporter gene, SLC6A4, in 1,231 people with autism. They also read it in 2,421 parents and 1,287 siblings.

They hunted for rare spelling changes that alter the protein. Then they asked: do people who carry these rare edits show more rigid or compulsive behaviors?

They found 21 rare coding variants, but the variants were just as common in controls. None of the edits tracked with repetitive behaviors.

Bottom line: rare SLC6A4 variants do not explain autism risk or rigid-compulsive traits.

Boswell et al. (2023) pooled 25 studies and saw no blood-level differences in the tryptophan-kynurenine pathway, the chemical road that feeds serotonin. Takeshi’s gene result and F’s metabolite result both say the same thing: the serotonin story is not a simple smoking gun.

Wang et al. (2010) ran a similar large screen for creatine-deficiency syndrome in autism and also came up empty. The pattern is clear: single rare metabolic hits are, well, rare.

Almatrafi et al. (2023) later found two brothers with autism who did carry a rare SLC6A8 creatine transporter mutation. This looks like a clash, but it isn’t. Large screens show population-level risk; case reports remind us that one-in-a-million kids still matter. You need both views.

Stop chasing SLC6A4 gene tests or serotonin supplements as routine autism work-ups. Use your assessment time to measure adaptive skills, sensory triggers, and reinforcement patterns instead. When a family asks about “serotonin genes,” you can give a data-backed answer: science looked hard and found no link.