Urea Cycle Disorders


Ornithine Transcarbamylase Deficiency (OTC)



Ornithine transcarbamylase (OTC) deficiency is a rare X-linked genetic disorder characterised by complete or partial lack of the enzyme ornithine transcarbamylase (OTC). OTC is one of six enzymes that play a role in the break down and removal of nitrogen the body, a process known as the urea cycle. The lack of the OTC enzyme results in excessive accumulation of nitrogen, in the form of ammonia (hyperammonemia), in the blood. Excess ammonia, which is a neurotoxin, travels to the central nervous system through the blood, resulting in the symptoms and physical findings associated with OTC deficiency. Symptoms include vomiting, refusal to eat, progressive lethargy, and coma.


The condition can be diagnosed during newborn period. Diagnosis can also be made when symptoms present at any age.


1:50,000 – 80,000 estimated worldwide.


The treatment of OTC deficiency is aimed at preventing excessive ammonia from being formed or from removing excessive ammonia during a hyperammonemic episode. OTC can be treated using a low protein, high calorie diet, micronutrients and the administration of essential amino acids.

During illness treatment will be different and you will need to ring your metabolic doctor/dietitian or the 24hour emergency number you have been given.

Support Links & Materials

Urea Cycle Disorders Handbook

UCD Fruit and Veg Counting Lists

UCD General Protein Counting Lists