In this context it is important to mention that elevated levels of soluble NCAM have been found in brains or cerebrospinal fluids of patients with Alzheimer disease, schizophrenia or medulloblastoma40, and that overexpression of soluble extracellular NCAM in mice causes defects in synaptic connectivity and produces abnormal behaviour relevant in schizophrenia and other neuropsychiatric disorders44. Here, NCAM1 is linked to early-onset autosomal dominant Alzheimer disease.