Genetic analysis of human infectious diseases has led to the identification and characterization of four types of inborn errors of immunity (IEI) associated with STAT1: (I) autosomal recessive (AR) complete STAT1 deficiency, (II) AR partial STAT1 deficiency, (III) autosomal dominant (AD) STAT1 deficiency, and (IV) AD gain of STAT1 activity (1, 2). The gene discussed is STAT1; the disease is Alzheimer disease.