Arginase Deficiency

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Arginase Deficiency is a rare inherited metabolic disorder.

Arginase Deficiency affects the way your baby breaks down protein. Many foods contain protein. The body needs protein for growth and repair. Many people eat more protein than the body needs.

To remove excess protein from the body: First, 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 have to take place. Each step needs an enzyme (like chemical scissors) for it to work. Arginine is formed in the urea cycle and then broken down to release urea. The enzyme that breaks down arginine is called arginase 1. The build-up of harmful chemicals can cause damage to the brain. It may cause delays to normal development like walking and talking.

In Arginase deficiency, the body lacks the enzyme arginase 1. This leads to high arginine levels. In some patients, it can also lead to raised ammonia levels, particularly at times of increased protein breakdown.

Arginase deficiency is a very rare disorder; it has been estimated to occur once in every 300,000 to 1,000,000 individuals.

Arginine is one of the building blocks from which protein is made, so we need some arginine in our blood. It is harmful, however, if the levels are too high. Children with Arginase deficiency may get:

• Stiff legs (spasticity)
• Learning difficulties
• Seizures
• Poor growth

Arginase deficiency sometimes leads to high ammonia levels, causing the patient to become drowsy or even comatose.

Ammonia levels can rise when there is an increased breakdown of protein. This may happen if too much protein is eaten. It commonly results from the breakdown of the body’s own protein. This is often triggered by infections, particularly if there is vomiting. This causes catabolism which is a breakdown of body protein and can lead to a metabolic crisis.

In Arginase deficiency it is important that enough protein is given to grow….but not too much as its breakdown will increase the arginine levels.

The diagnosis is suspected in a patient with high arginine levels in the blood. The diagnosis is confirmed by finding the mutation in the ARG1 gene.

Arginase Deficiency can be managed with the following:

• A protein restricted diet
• A special amino acid supplement
• Sufficient energy supply from food and feeds
• Regular feeding
• 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 childhood illness, an emergency regimen is given. This is to avoid a lack of energy supply and build-up of ammonia. During illness:

• Stop all protein in food & drink
• Start the emergency regimen. This is made up of glucose polymer
• Continue medication as prescribed

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.

If you have Arginase Deficiency you will need to be monitored frequently. This includes:

• 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

Take home messages:

• Arginase 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 management

Helpful hints:

• Always ensure you have a good supply of your dietary products and that they are in date.
• Your dietary products 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.

Humans have chromosomes composed of DNA. Genes are pieces of DNA that carry the genetic instruction. Each chromosome may have several thousand genes.

The word mutation means a change or error in the genetic instruction.

We inherit particular chromosomes from the egg of the mother and sperm of the father.

The genes on those chromosomes carry the instruction that determines characteristics, which are a combination of the parents.

Arginase Deficiency is an inherited condition. There is nothing that could have been done to prevent your baby from having Arginase Deficiency.

Everyone has a pair of genes that make the arginase 1 enzyme. In children with Arginase Deficiency, neither of these genes works correctly. These children inherit one non-working Arginase Deficiency gene from each parent.

Parents of children with Arginase Deficiency are carriers of the condition. Carriers do not have Arginase Deficiency because the other gene of this pair is working correctly.

When both parents are carriers, in each pregnancy the risk to the baby is as follows:

• 25% chance (1 in 4) of Arginase Deficiency
• 50% chance (1 in 2) for the baby to be a carrier of Arginase Deficiency
• 25% chance (1 in 4) for the baby to have two working genes and neither have Arginase Deficiency or be a carrier

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 written by Burgard and Wendel. The TEMPLE Guides are supported by Nutricia. Dated February 2017.

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