Multiple studies show mixed pieces of evidence with regards to serum IGF-1 concentration and the long-term neuroprotective effects, tolerability, safety, and efficacy of IGF-1 in many CNS disorders, most notably stroke, traumatic brain injury, amyotrophic lateral sclerosis, Alzheimer’s disease, autism spectrum disorder, and others. Here, IGF1 is linked to early-onset autosomal dominant Alzheimer disease.