A rare inherited urea cycle disorder caused by lack of enzymes (argininosuccinase lyase) needed to turn ammonia into urea resulting in excess ammonia in the body. The late onset form of the condition tends to start later in life as there is some level of activity by the defective enzyme. The condition tends to be less severe and can be triggered by a change in diet, illness or some other stress on the body. See also Argininosuccinase lyase deficiency, late onset