Hydroxykynureninuria

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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.  

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

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.   

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.

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.  

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  

References are available on request. Please contact us on 0800 652 3181 or by emailing contact@metabolicsupport.org.

Please note calls to 0800 numbers are free from UK landlines and mobiles. Calls from business lines may be charged – please check with your provider.

This information about metabolic diseases is provided by Metabolic Support UK and is intended for educational purposes only. It should not be used for diagnostic or treatment purposes.

Should you require more detailed information please contact Metabolic Support UK by email (contact@metabolicsupport.org) or by telephone ( 0800 652 3181). For specific medical information regarding a disorder or individual please contact your GP or Paediatrician. Metabolic Support UK accepts no responsibility for any errors or omissions nor does Metabolic Support UK assume any liability of any kind for the content of any information contained within this summary or any use that you may make of it.