Xanthinuria type 2
What else is it called?
- Type 2 Xanthinuria
- XDH and AOX dual deficiency
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What causes it?
Xanthinuria type 2 is a rare autosomal recessive condition which is caused by a defect in the metabolism of purines. Purines are referred to as nucleotides, they are responsible for enabling DNA production and DNA replication. This defect to the metabolism of purines impacts the synthesis of a cofactor called molybdenum, this is needed to produce the enzymes XDH and AOX1, these 2 enzymes are needed to break down the molecule xanthine and prevent a build-up of this molecule in the body. It is currently unclear which gene is responsible for this metabolic condition, research persists in this area.
How common is it?
Due to the rarity of this condition, it is not possible to determine how many people have been diagnosed with Xanthinuria type 2. It is also unclear if this condition is more common in females or males or in particular ethnicities.
What are the signs and symptoms?
It can be quite variable as to what age signs and symptoms may become apparent. It has previously been reported that most individuals will remain symptomless with this condition. Some of the more common symptoms that you may experience with this condition are:
- Kidney stones
- Renal failure
- Renal cysts
- Urinary tract infections
- Large intestine ulceration
- Floppy head due to xanthine accumulation in muscles
How is it diagnosed?
Excretion via urination of very large amounts of xanthine are a sign that someone would have this condition. This sample would be analysed via a urine test to check for elevated levels of this metabolite. It is also common for people with this condition to have high levels of hypoxanthine circulating in blood and low blood uric acid levels. Therefore this may also be diagnosed via a blood test alongside the expression of signs and symptoms that are associated with this condition.
Can it be treated?
Treatment options for this condition is very limited. Symptoms are usually managed as they present, this will be discussed with you when you have been diagnosed.
Do my family need to be tested?
Xanthinuria type 2 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.
If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.
Once you are diagnosed, you can speak to a genetic counsellor. They can explain how you may have inheritedXanthinuria type 2 is. They can also tell you about genetic testing for the rest of your family. They can provide advice and support if you go on to have children of your own.
If you have previously had a child with Xanthinuria type 2 is and go on to have further children, their New-born Screening test should be carried out within 24-48 hours of birth.