Ornithine Transcarbamylase (OTC) Deficiency
OTC is an inherited disorder that belongs to a class of genetic diseases called urea cycle disorders. In OTC, the urea cycle is unable to proceed normally which then causes ammonia to accumulate in the blood. When ammonia levels become too high it is toxic to your body. The nervous system is most commonly affected by elevated ammonia. OTC is noted to be the most common hereditary urea cycle abnormality.
How OTC Works
The urea cycle is a process in which your body removes waste (ammonia) from the body. The liver produces enzymes that change the ammonia into urea and then can be eliminated through urine. This process is disrupted in OTC as the liver is unable to make the enzymes to break down ammonia resulting in high ammonia levels.
Diagnosis
Blood testing can determine if there are excessive amounts of ammonia in the blood. High levels of ammonia may characterize other disorders as well. DNA genetic testing would be performed to confirm a diagnosis of OTC as part of a thorough genetics work up.
Symptoms
Age of onset varies from person to person, even within the same family. A severe form of the disorder affects some infants, typically males, shortly after birth, usually following a protein feeding.
Initial symptoms may include:
- Poor or refusal to eat
- Poor suck
- Vomiting
- Progressive lethargy
- Irritability
OTC can rapidly progress to more severe symptoms including:
- Seizures
- Diminished muscle tone
- Enlarged liver
- Respiratory difficulty
Treatment
A multidisciplinary team approach involves pediatricians, neurologists, geneticists, dieticians and physicians. Treatment for OTC deficiency is aimed at preventing excessive ammonia from being formed or removing excessive ammonia. Dietary restrictions in individuals with OTC deficiency are aimed at limiting the amount of protein intake to avoid the development of excess ammonia. Infants with OTC deficiency are placed on a low protein, high-calorie diet supplemented by essential amino acids. Additionally, patients with OTC deficiency are treated by medications that stimulate the removal of nitrogen from the body.
Affected Populations
OTC deficiency is inherited as an X-linked genetic condition. OTC deficiency affects males more often than females and is fully expressed in males only. In males, symptoms typically begin during the first few days of life, however late-onset OTC deficiency can present later in life. Approximately 20% of carrier females have mild symptoms of the disorder and are rarely severely affected in childhood.
Liver Transplant
For those with more severe or non-responsive cases of OTC who progress towards liver failure, the next treatment option is liver transplantation. Fortunately, this group of patients has a favorable long-term outlook.
We understand that learning your child has a metabolic disorder or any other chronic medical condition can be a very stressful time for your family. That’s why the SLUCare Physician Group at SSM Health Cardinal Glennon Children’s Hospital are here to support you every step of the way. Call us at 314-268-4010 to schedule an appointment.