What else is it called?

Hydroxykynureninuria is also known as: 

  • Xanthurenic aciduria  
  • Kynureninase deficiency  
  • Kynureninase deficiency partial 

Get in touch

Contact our caring team on 08452 412 173 for help and support. Our phone lines open 10am-4pm, Monday to Friday.

Prefer to email? Our email address is contact@metabolicsupportuk.org.

What causes it?

Hydroxykynureninuria is caused by a problem in the gene that produces Kynureninase. This an enzyme which helps breakdown an amino acid known as tryptophan. this leads to the excessive amounts of xanthurenic acid, 3-hydroxykynurenine and kynurenine to be found in the urine.  

How common is it?

The prevalence of Hydroxykynureninuria is less than 1:1,000,000 worldwide. 

What are the signs and symptoms?

The signs and symptoms vary between different people diagnosed with Hydroxykynureninuria, the signs and symptoms usually present during infancy and they are:  

  • Encephalopathy (brain disease)  
  • Breathing problems 
  • Sensorineural or other hearing impairment which may be apparent from birth (congenital) 
  • Dry skin  
  • Development delay  
  • Headache  
  • High muscle tone (hypertonia) 
  • Low blood pressure (hypotension) 
  • Intellectual disability  
  • Metabolic acidosis  
  • Accumulation of acid in the body due to kidney problems (Renal tubular acidosis)  
  • Repetitive and aimless movements (Stereotypy)  
  • Inflammation of the mouth and/or lips (stomatitis)  
  • Increased heart rate (Tachycardia)  
  • Coma 
  • Aminoaciduria (high levels of amino acids in the urine) 
  • Hearing impairment  
  • Anaemia 
  • Diarrhoea  
  • Enlarge liver (hepatomegaly)  
  • Photosensitivity  
  • Large spleen 

If this condition is left undiagnosed it may lead to death.   

How is it diagnosed?

This disorder can be diagnosed using genetic analysis. It can also be diagnosed by taking samples of blood and urine may also be taken.  

Currently the following countries are diagnosing Hydroxykynureninuria:  

  • The United Kingdom  
  • Sweden  
  • Netherlands 
  • Italy  
  • Germany  
  • France  
  • Estonia  
  • Canada  
  • Belgium  
  • United States 

These countries are testing for Hydroxykynureninuria using molecular genetics, biochemical genetics, analyte, enzyme assays and whole exome sequencing.

Can it be treated?

Currently there are two orphan drugs currently available these are sodium phenylacetate and sodium benzoate which are based in the United States and being used to treat Hydroxykynureninuria. All other treatment is based on the management of symptoms and providing support for you and your family.  

Do my family need to be tested?

Hydroxykynureninuria is an autosomal recessive inherited metabolic disorder. Humans have chromosomes which are composed of DNA and genes are sections of DNA that carry out a genetic instruction, for example making a protein. Humans are made up of 46 chromosomes and we inherit 23 from each of our parents in the form of the egg and the sperm cells. These chromosomes combine to make 46 and they determine a person’s characteristics, for example eye colour. Every person on earth has a pair of genes that are used to make Kynureninase. When a child has inherited two non-working genes from their parents then they develop Hydroxykynureninuria.  

The parents of the children with Hydroxykynureninuria do not need to be diagnosed with Hydroxykynureninuria, they’re known as carriers. A carrier is a person that carries one non-working form of the gene, but they do not have the disorder because the other gene in the pair is working correctly. When both parents are carriers of the disorder, the risk of the child developing Hydroxykynureninuria is as follows:  

  • There is a 25% chance that the child is unaffected and not a carrier 
  • There is a 50% chance that the child is unaffected and is a carrier 
  • There is a 25% chance that the child is affected by Hydroxykynureninuria  


Relevant Organisations


References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing helen@metabolicsupportuk.org [Resource Library No: AAP002]. 

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