To investigate the role of N-APP/DR6/caspase 6 pathway in the development of hippocampal Alzheimer’s disease (AD)-associated pathology, we examined DR6 immunoreactivity (IR) in the developing hippocampus from patients with Down syndrome (DS; 48 brain specimens; 14 to 41 gestational weeks; 7 days to 8 months postnatally; 15 to 64 years) and in adults with DS and AD. Here, TNFRSF21 is linked to early-onset autosomal dominant Alzheimer disease.