Deoxyguanosine kinase deficiency

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Deoxyguanosine kinase deficiency is an inherited disorder that can disrupt the normal function of the liver, brain, and muscles. Researchers have described different forms of this disorder. Approximately 75 percent of affected individuals have the hepatocerebral form, which causes serious problems in the liver (hepato-) and brain (cerebral). Approximately 20 percent of people with deoxyguanosine kinase deficiency have the isolated hepatic form, which causes liver disease without serious neurological problems. The myopathic form is the least common form; it affects approximately 5 percent of people with deoxyguanosine kinase deficiency. The myopathic form causes problems with the skeletal muscles, which are the muscles used for movement. The signs and symptoms of deoxyguanosine kinase deficiency can vary, even among members of the same family.

Infants with the hepatocerebral form of deoxyguanosine kinase deficiency typically have low blood glucose levels (hypoglycemia) and a buildup of lactic acid in the body (lactic acidosis) soon after birth. Within the first few weeks of life, these infants typically begin to show signs of liver disease and brain dysfunction. Neurological signs and symptoms may include weak muscle tone (hypotonia), abnormal involuntary eye movements (nystagmus), developmental delays, and, rarely, seizures. Early signs of liver disease may include an enlarged liver (hepatomegaly) and yellowing of the skin and the whites of the eyes (jaundice). Liver disease usually progresses to liver failure.

Signs and symptoms of the isolated hepatic form of deoxyguanosine kinase deficiency may appear soon after birth or during childhood. Like those with the hepatocerebral form, people with the hepatic form often have liver disease that worsens over time and may progress to liver failure. Some affected individuals have additional signs and symptoms that indicate the involvement of other body systems, such as the kidneys and the heart.

Signs and symptoms of the myopathic form often appear in adulthood, although they sometimes appear earlier in life. In addition to problems with the skeletal muscles, people with the myopathic form of deoxyguanosine kinase deficiency can have heart problems, brain abnormalities, or weakness of the eye muscles. People with the myopathic form typically do not have liver disease.

Without intervention, most individuals with deoxyguanosine kinase deficiency have a shortened life expectancy. Those with liver disease typically do not survive past early childhood, while those with the myopathic form may survive into middle or late adulthood.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

The DGUOK gene provides instructions for making the enzyme deoxyguanosine kinase. This enzyme plays an important role in mitochondria, which are the energy-producing centers inside the cell. Mitochondria each contain their own DNA, known as mitochondrial DNA or mtDNA, that is essential for their normal function. Deoxyguanosine kinase is involved in producing and maintaining the building blocks (nucleosides) that make up mtDNA.

The variants (also called mutations) in the DGUOK gene that cause deoxyguanosine kinase deficiency reduce or eliminate the activity of the deoxyguanosine kinase enzyme. Reduced enzyme activity leads to problems with the production and maintenance of mtDNA. A decrease in the amount of mtDNA (known as mitochondrial DNA depletion) impairs mitochondrial function in many of the body's cells and tissues. These problems lead to the brain, liver, and muscle dysfunction associated with deoxyguanosine kinase deficiency.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell must have a variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

More than 200 individuals with deoxyguanosine kinase deficiency have been reported in the medical literature. The prevalence in the general population is estimated to be approximately 1 in 114,000 individuals.

Which doctor should you see?

The suggested department for discussing Deoxyguanosine kinase deficiency is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Deoxyguanosine kinase deficiency. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.