Argininosuccinate lyase (ASL) deficiency, also known as Arginosuccinic aciduria, is an inherited disorder caused by accumulation of ammonia in the blood, due to a deficiency of the enzyme argininosuccinate lyase. Normally the body changes ammonia into urea which can be removed in the urine. People with ASL deficiency can't efficiently convert ammonia into urea, and ammonia will subsequently build up in their body. Highly elevated ammonia level is toxic to the body and may cause damage to the brain. If not treated promptly, babies with ASL deficiency normally show symptoms shortly after birth which may include lack of energy, poor appetite, breathing problems, lack of control of body temperature, seizures and coma. Other effects include developmental delay, intellectual disability, liver damage, skin lesions and brittle hair. Without treatment, affected babies may die within the first few weeks of life. There is no cure for ASL deficiency, though strict dietary management and liver transplantation have shown to have some effect on reversing or correcting some symptoms. ASL deficiency is caused by pathogenic variants in the ASL gene.