Neuregulin 3 (NRG3), a specific ligand for ErbB4 and a neuronal-enriched neurotrophin is implicated in the genetic predisposition to a broad spectrum of neurodevelopmental, neurocognitive and neuropsychiatric disorders, including Alzheimer's disease, autism and schizophrenia. This evidence concerns the gene NRG3 and early-onset autosomal dominant Alzheimer disease.