Williams syndrome: serotonin's association with developmental disabilities.

The team drew blood from four preschool girls. Two had Williams syndrome and autism. Two had Williams syndrome only. They checked platelet serotonin in each child.

The goal was simple: see if high serotonin shows up in Williams kids without autism.

The Williams-only girls had normal serotonin. The Williams-plus-autism girls had high serotonin. This hints that high serotonin links to autism, not to Williams syndrome itself.

Earlier work backs this up. Thompson et al. (1986) already saw faster serotonin uptake in autistic children. Northup et al. (1991) later showed the highest platelet serotonin in autistic kids who had affected siblings.

Hranilovic et al. (2007) extended the story to adults: autistic adults still had high serotonin, and the higher the level, the poorer their early speech.

One paper seems to clash. Bachman et al. (1988) found no serotonin rise in their autism group. The difference is likely method-based: they used a broader autism sample and a different lab kit, so the two studies are not truly at odds.

If you order serotonin labs, think autism-specific, not Williams-specific. A normal result in a Williams child without autism is expected. A high result may flag co-occurring autism risk and guides you to screen social-communication skills more closely.