Striatal-enriched tyrosine protein phosphatase (STEP), encoded by the Ptpn5 gene, is a neuron-specific phosphatase that regulates synaptic function and plasticity, whereas its dysregulation is associated with neurodegenerative diseases including Alzheimer’s disease (AD) [1,2]. Here, PTPN5 is linked to early-onset autosomal dominant Alzheimer disease.