Cerebrospinal fluid indoleacetic acid in autistic subjects.

Researchers drew spinal fluid from autistic and non-autistic adults. They measured levels of indoleacetic acid, a chemical left over after serotonin is used in the brain. The goal was to see if this acid was higher or lower in people with autism.

The study used a case-control design. This means they compared one group with autism to a matched group without it.

The acid levels were the same in both groups. No significant difference showed up. This suggests the brain's serotonin-use pathway works normally in autism.

Because the numbers did not differ, the marker cannot help diagnose autism or guide treatment.

The result lines up with other null findings. Marcell et al. (1988) also found no brain-structure differences in the same year. Bromley et al. (1998) later saw no hippocampus volume change, and Porter et al. (2008) found no blood BDNF differences. Together, these studies show that simple single biomarkers rarely split autism from non-autism.

A 2020 EEG paper by J et al. adds another layer. It looked at prediction-error brain waves and again found no group gap. The pattern is clear: many biological measures once hoped to flag autism end up flat when tested in controlled designs.

On the surface, Chezan et al. (2019) seems to disagree. Their review of scalp-acupuncture trials reported small but positive reductions in autism severity. The key difference is intervention versus biology. The 1988 study asked, "Is the marker different at baseline?" The 2019 review asked, "Can a treatment change behavior?" Both can be true: the acid level is normal, yet some external therapy might still help symptoms.

You can stop chasing spinal-fluid indoleacetic acid as a diagnostic tool. Save your clients from lumbar punctures that yield no actionable data. Instead, put your effort into functional behavior assessments and evidence-based interventions that do show benefit.