Infant-onset UCDs
The earlier the symptoms occur in an infant the more severe the defect. Symptoms within the first five days of life indicate a total blockage in the urea cycle with no protein breakdown occurring. Ornithine Transcarbamylase Deficiency, which occurs only in boys and Carbamyl Phosphate Synthetase Deficiency that occurs in both sexes, are the most severe because they occur earlier in the urea cycle.
Adult (late-onset) UCDs
Children and adults who present with symptoms have milder deficiencies in the urea cycle. Symptoms often begin with cyclical vomiting, lethargy, sleep disorders, delusions, hallucinations, and psychosis. Generally their deficiencies tend to occur later in the urea cycle and may be incomplete blockages.
References:
7. Summar, Marshall, MD and Tuchman, Mendel, MD, “Proceedings of a consensus conference for the managaement of patients with urea cycle disorders” Journal of Pediatrics, Vol. 128, No. 1, p. S6-10.