This process converts the toxic ammonia produced during protein breakdown into urea for excretion. Urea cycle disorders are a group of rare genetic conditions that result from enzyme deficiencies in the urea cycle. This causes toxic levels of ammonia to accumulate in the bloodstream, which can damage the brain and be life-threatening. The most common urea cycle disorders are ornithine transcarbamylase (OTC) deficiency, citrullinemia types I and II, argininosuccinic aciduria, and arginase deficiency.