First identified in 1990, aromatic l-amino acid decarboxylase (AADC) deficiency is an extremely rare, debilitating, inherited neurological disorder. The disease typically manifests in the first year of life and, although some patients have relatively mild phenotypes, most have severe, debilitating, sometimes life-threatening, phenotypes. Timely and accurate diagnosis is vital for patients to benefit from emerging treatments to prevent neurological damage, especially given the availability of gene therapy. This book is intended to help all clinicians, but in particular neonatologists, pediatricians, and pediatric neurologists, become more familiar with AADC deficiency, including the diagnostic and therapeutic options for practicing physicians so that patients can receive the best possible clinical care.