Deoxyguanosine Kinase Deficiency

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This disorder is caused by a problem with the DGUOK gene. This gene provides instructions for

making the deoxyguanosine kinase enzyme which is needed for the production and maintenance of mitochondrial DNA. Mitochondria, which has its own DNA, converts energy from food into energy usable by cells.

If you have a problem in this gene, you will not produce enough deoxyguanosine kinase enzyme. Therefore, it will affect the normal mitochondrial function in many cells and tissues.

We do not know how many people have this disorder. It is very rare with only a small amount of cases that are known. Is also unknown whether it is more common between males and females or any specific ethnicities. Collectively, it is estimated that Deoxyguanosine kinase deficiency accounts for 15 % – 20 % of all cases of various mitochondrial DNA depletion syndromes.  

here are two forms of this disorder. The more severe variant, which is called hepatocerebral and has its onset soon after birth, affects the majority of individuals with the Deoxyguanosine kinase deficiency. A minority of individuals have the milder form with the onset later in infancy or childhood as mostly hepatic disease. 

 The signs and symptoms of the more severe hepatocerebral variant may include: 

• Buildup of lactic acid in the body (lactic acidosis) 
• Weakness 
• Behavior changes such as poor feeding and decreased activity, and vomiting  
• Low blood sugar (hypoglycemia) 
• Liver disease which may result in liver failure 
• Yellowing of the skin, mucous membranes, and whites of the eyes (jaundice)  
• Enlarged liver (hepatomegaly) 
• Elevated transaminases 
• Progressive neurological problems:  

• Very weak muscle tone (severe hypotonia) 
• Abnormal eye movements (nystagmus) 
• Loss of skills they had previously acquired (developmental regression) 

The prognosis for the severe hepatocerebral variant is poor. Most affected children will not survive past 4 years of age.  

The signs and symptoms of the less severe variant may include: 

• Liver disease
• Yellowing of the skin, mucous membranes, and whites of the eyes (jaundice)  
• Enlarged liver (hepatomegaly) 
• Elevated transaminases 
• Kidney problems 
• Mild form of weak muscle tone (mild hypotonia) 

 The less severe variant is often triggered by a viral illness.  

You will be diagnosed after a clinical examination by your specialist or doctor. However, as the signs and symptoms of this disorder are similar to other conditions, you will need further tests. Doctors will analyse your blood by conducting a specialized blood test. You will also need to undertake a liver biopsy. The deficiency can be detected by newborn screening. Unfortunately, not in the UK. DNA tests confirm the diagnosis. 

Unfortunately, there is no available cure for this disorder. Therefore, treatment is focused on managing individual symptoms and providing comfort and relief in the form of supporting the individual and any family members. A multi-disciplinary team of specialists and support networks will be involved in the management of the condition and to offer practical and emotional support. 

Feeding problems may require feeding therapy and/or the implementation of a gastronomy tube. Specialists may be needed to provide medical, dietary, developmental, social, and educational support. Children with liver disease may require formulas with enriched medium-chain triglyceride content and fractional meals with enteral nutrition at night. Some may need a cornstarch-based diet. Supplementation with fat-soluble vitamins and essential fatty acids is also advised. If you have no or mild neurological involvement, you may benefit from liver transplantation. 

Deoxyguanosine kinase deficiency 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 inherited Deoxyguanosine kinase deficiency. 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. 

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