Ornithine transcarbamylase deficiency (OTC) is an inherited disorder characterized by damage to the nervous system due to the accumulation of toxic levels of ammonia in the bloodstream. This accumulation is due to a deficient enzyme called ornithine transcarbamylase. The more severe form of OTC is mostly seen in males with symptoms typically appearing the second or third day of life. These infants appear normal at birth and rapidly become very ill. Their muscle tone weakens, they may refuse to eat, and begin to hyperventilate as their body temperature drops. They may also have seizures. Once a diagnosis has been made, treatment begins right away that can stabilize ammonia levels in these infants, though episodes of increased levels of ammonia in the bloodstream can still easily occur in spite of adherence to a strict treatment. Typically a liver transplant is needed by six months of age for these infants affected with OTC. Brain damage is possible during these episodes, which can cause variable amounts of intellectual disability and decreased control over muscle movement. Some males, and even some females, may not have symptoms until later on in childhood, adolescence or adulthood. Symptoms tend to be milder and episodes of increased levels of ammonia occur less often. Females appear to be especially at risk in the postpartum period for levels of ammonia to rise. There is no cure for OTC. Treatment for OTC includes strict, life-long dietary and supplemental management. Some babies may require dialysis to help lower ammonia levels. In general, the more severe the symptoms and the number of episodes, the shorter the life expectancy is for individuals with OTC. OTC is caused by pathogenic variants in the OTC gene.