Citrullinemia is a rare genetic disorder that affects the body's ability to process certain proteins. It is caused by a deficiency in the enzyme argininosuccinate synthetase, which is essential for the urea cycle. This cycle helps remove ammonia from the bloodstream, and without proper function, ammonia can build up, leading to serious health issues. Symptoms of citrullinemia can include vomiting, lethargy, and seizures, particularly during periods of illness or stress. Early diagnosis and treatment are crucial to manage the condition, often involving a special diet and medications to help reduce ammonia levels in the body.