Kinetics of 3H-serotonin uptake by platelets in infantile autism and developmental language disorder (including five pairs of twins).

Researchers drew blood from kids with autism and kids with language delays. They also took blood from kids who were developing normally. The team measured how fast each child's platelets pulled serotonin out of the blood. Five pairs of twins were in the study to check if genes matter.

Platelets from autism and language-delay kids grabbed serotonin faster than platelets from typical kids. The twin data hinted this fast uptake runs in families. The authors said the speed difference could become a lab marker for autism risk.

Cohen et al. (1990) repeated the idea in parents instead of twins. They found high whole-blood serotonin clustered in autism families too, backing the genetic story. Northup et al. (1991) also saw highest platelet serotonin in kids who had an autistic brother or sister, strengthening the familial link.

Bachman et al. (1988) seems to clash — they saw no serotonin difference between autistic and typical kids. The gap is real but small: Thompson et al. (1986) tested uptake speed, while Bachman et al. (1988) tested how much serotonin was already inside the platelets. Different lab numbers, different answers.

Hranilovic et al. (2007) pushed the finding further by testing adults. Higher serotonin still showed up, and it tracked with poorer speech history, hinting the marker may stay stable across life.

You now have a possible biological flag that can sit in a medical chart next to behavioral scores. If you serve a child with language delays, asking the pediatrician for a simple platelet test could add evidence for or against an autism trajectory. Do not treat the number yet — no drug dose follows from it — but do use it to start family conversations about genetic risk and early intervention intensity.