Relationship Between Early Social-Emotional Behavior and Autism Spectrum Disorder: A High-Risk Sibling Study.

Levinson et al. (2020) followed baby brothers and sisters of kids with autism. These "high-risk" infants are more likely to get an ASD diagnosis later.

Parents filled out the Infant-Toddler Social-Emotional Assessment when each baby turned 18 months. The team later checked which toddlers received an ASD diagnosis.

ITSEA scores at 18 months did separate the toddlers who later got ASD from those who did not. The gap was real but small.

The test missed many future ASD cases. Low sensitivity means you cannot rely on ITSEA alone to rule autism in or out.

Gunderson et al. (2021) pushed the window even earlier. They saw sensory gaps in the same high-risk babies at 12 months. Liu et al. (2024) found gesture problems at 12-13 months. Together these studies show ASD signs can pop up sooner than 18 months.

Lemcke et al. (2013) looked at parent red flags in a big general cohort and found almost no predictive power at 18 months. That seems to clash with Sarah's small positive result. The difference is risk level: Sanne studied all comers while Sarah focused only on siblings already at high risk. In other words, parent report is weak in the general population but holds a little signal in the highest-risk group.

Smit et al. (2019) tested temperament questionnaires in high-risk infants and also got group-level differences with poor individual accuracy. The pattern matches Sarah's: parent questionnaires help sort groups yet fail as standalone diagnostic tools.

If you screen baby siblings, treat the ITSEA as a first pass, not a verdict. Pair it with sensory checks at 12 months and gesture probes soon after. Always add direct observation and follow-up visits. The modest sensitivity means a negative score does not clear the child; watch and re-screen every six months.