Lysinuric Protein Intolerance
What else is it called?
- Congenital Lysinuria
- Hyperdibasic Aminoaciduria
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What causes it?
Lysinuric Protein Intolerance [LPI] is an inherited metabolic disorder in which the body cannot process specific amino acids. These amino acids are lysine, arginine, and ornithine. Amino acids are the building blocks of protein. If you eat a high amount of protein, you may experience nausea and vomiting which occurs because of the body’s inability to digest these foods.
This condition is believed to be caused by a fault the SLC7A7 gene. This gene is responsible for making the protein, y+L amino acid transporter 1. This protein helps to transport lysine, arginine and ornithine which enables the body to use them. Arginine and ornithine are involved in the urea cycle which helps to remove ammonia from the body. Lysine helps to strengthen connective tissues such as tendons, ligaments, and skin. The genetic fault in this condition means that the body has a shortage of the three amino acids, and this can cause high levels of ammonia in the blood (hyperammonaemia) as a result of arginine and ornithine deficiency and short stature and osteoporosis (brittle bones) due to lysine deficiency.
How common is it?
Current research suggests that this metabolic condition impacts 1 in 60,000 newborns in the region of Finland and 1 in 57,000 in regions of Japan. Instances in other areas are less known, this may be due to the rarity of this condition. Due to this rarity, it is unclear whether this condition is more common in males or females or with specific ethnicities.
What are the signs and symptoms?
Symptoms can appear in late infancy once a child has been weaned onto solid foods containing protein. Symptoms may include:
- Enlarged spleen
- Enlarged liver
- Impaired immune function
- Increased susceptibility to developing osteoporosis
- End stage renal disease (caused by protein in the kidney)
- Failure to grow and gain weight (failure to thrive)
- Lung and kidney dysfunction
Occasionally, individuals also develop pulmonary alveolar proteinosis which is caused by a build-up of protein in the lungs which can lead to life-threatening problems. A lack of certain proteins within the body may also see an increase in ammonia levels within the body which can be harmful and if not managed correctly may be fatal
How is it diagnosed?
LPI can be diagnosed by noticing the expression of physical symptoms related to LPI a physical examination and a detailed patient history may lead to further investigations. It may also be queried if you have a family history of this condition. This condition can be accurately diagnosed by genetic testing for a SLC7A7 gene mutation.
Can it be treated?
Treatment is usually aimed at avoiding high protein meals containing lysine, arginine, and ornithine. A specialist dietitian will advise you on which foods to avoid and may also recommend supplements or protein replacements to ensure you maintain a balanced diet. Dietary changes should not be made without the advice of a specialist dietitian. Medication can also be prescribed to help prevent the build-up of nitrogen and ammonia within the body. Other treatment is based on individual symptoms. Earlier diagnosis and prompt correct management improves prognosis.
Do my family need to be tested?
LPI can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier.
If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have.