Ornithine Transcarbamylase Deficiency
What else is it called?
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What causes it?
OTC is an inherited metabolic condition. Many foods contain protein. The body needs protein for growth and repair. Many people eat more protein than the body needs.
How do we remove waste protein from the body?
- Firstly, the body converts waste protein to a toxic chemical called ammonia
- Ammonia is then converted into a non-toxic chemical (urea) in the liver
- This process occurs via the urea cycle
- In the urea cycle, several steps must take place. Each step needs an enzyme for it to work
- Urea is then removed by the kidneys
In OTC deficiency, the body lacks an enzyme called ornithine transcarbamylase. This means the liver cannot convert waste protein into urea as fast as normal. It can lead to high ammonia levels, particularly at times of increased protein breakdown.
Ammonia levels can rise when there is an increased break down of protein. This may happen if too much protein is eaten. It commonly results from break down of the body’s own protein. This is often triggered by infections or other factors which increase stress on the body. This causes catabolism which is a break down of body protein and can lead to a metabolic crisis.
How common is it?
OTC is estimated to affect between one in every 56,500 to one in every 77,000 people.
What are the signs and symptoms?
Some babies become ill in the first few days of life whereas others may be diagnosed at a later age. Signs and symptoms can include:
- Poor feeding
- Excessive sleepiness
- Rapid breathing
- Dehydration (lack of body fluids)
The effects of high ammonia can quickly become life-threatening if untreated.
Some children may be diagnosed at a later stage
Signs and symptoms:
- Repeated episodes of
- vomiting, which may lead
- to sleepiness and coma
- Learning difficulties
What are the long term effects of OTC deficiency?
- It may cause learning difficulties.
- It may also cause delays to normal development like walking and talking.
Protein balance is needed in OTC deficiency. In OTC deficiency it is important that enough protein is given to grow… but not too much as it will make waste protein causing high ammonia levels.
Once diagnosed the condition is generally well managed and you can continue with day to day activities and remain perfectly well. However, symptoms can arise suddenly, and you may begin to feel unwell. With age and awareness of the individual effects of high ammonia, people tend to become more in tune with their body and so it is important that if you feel unwell or are concerned, you follow your emergency regimen and contact your metabolic team for advice.
It is vital that this is done quickly as the effects of high ammonia can quickly become life-threatening if untreated.
How is it diagnosed?
The diagnosis is suspected in a patient with high ammonia levels because of the pattern of chemicals in the blood and urine. The diagnosis is confirmed by finding a mutation in the OTC gene.
Can it be treated?
OTC deficiency is managed with the following:
- A protein restricted diet
- Sometimes a special amino acid supplement may be needed
- Sufficient energy supply from food and feeds
- Regular feeding
- Arginine or citrulline supplements
- Vitamin and mineral supplements
- Other medications to control the level of ammonia in the blood
Tube feeding may be necessary to give regular feeds. This will ensure energy, nutrient and fluid needs are met.
During any illness, an emergency regimen is given. This will reduce the break down of protein and the build-up of ammonia
- Stop all protein in food & drink
- Start the emergency regimen. This is made up of glucose polymer
- Continue medication as prescribed
Checklist for illness:
- Always take full amounts of emergency feeds as prescribed
- If symptoms continue and/or you are worried, go immediately to the hospital
- Regularly update your metabolic team
It is imperative that emergency feeds are started promptly and there are no delays in management.
How is OTC monitored?
- Frequent blood tests to check amino acids, nutrient and chemical levels
- Height and weight
- Developmental checks
- Diet and medications are adjusted according to age, weight and blood chemical levels
OTC deficiency is a serious inherited metabolic disorder that can lead to severe problems. The condition is managed with a protein restricted diet, regular feeding and medications. Remember, during illness, it is imperative that emergency feeds are started promptly, followed strictly and there are no delays in treatment.
Always ensure you have a good supply of your dietary products and medicines and that they are in date. Your dietary products and medications are prescribed. These are obtained via a pharmacy or home delivery. Always ensure you have your emergency feed products and a written emergency plan. Medications to control fever should be given as normally recommended – always keep supplies available.
Do my family need to be tested?
Genes are the instructions for how we are made. They are inherited from our parents. The OTC gene has the instructions for making this enzyme. Genes are composed of DNA. A mutation is a change in the DNA that leads to faulty instructions. People with OTC deficiency have a mutation in the OTC gene.
Our genes are arranged on chromosomes. Each chromosome carries hundreds of genes. Humans have 23 pairs of chromosomes. In females, this includes a pair of X chromosomes. Males have one X chromosome and one Y chromosome. This means males only have one copy of the genes on the X chromosome.
Cells are designed to have one working copy of the X chromosome so, in females, one X chromosome is inactivated in each cell.
The OTC gene is found on the X chromosome. All males with OTC deficiency are expected to have problems because they have no normal copies of the gene.
Females with a mutation of the OTC gene may never get problems, because their second copy of the gene is normal. They are said to be carriers. Some carrier females do get problems; they are said to be manifesting carriers. This happens if the X chromosome with the normal copy of the OTC gene has been inactivated in most of their cells.
References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing email@example.com [Resource Library No: OAP010].
This information is from the TEMPLE Guides which have been adapted by the Dietitians Group of the British Inherited Metabolic Disease Group (BIMDG) and is based on the original TEMPLE Guides written by Burgard and Wendel. The TEMPLE Guides are supported by Nutricia.