Thymidine kinase 2 (TK2) deficiency

What happens in this disease?

TK2 deficiency is an inherited disease that affects the mitochondria, the power plants of the cells. The TK2 gene helps to protect the mitochondria's own DNA. When this gene does not work, the muscles cannot produce enough energy. As a result, the muscles gradually become weaker.

Which symptoms can occur?

Symptoms often begin in infancy or early childhood. How severe the disease is and how fast it progresses vary greatly from person to person. The early-onset type progresses faster and can shorten life. Intelligence is usually not affected.

• Increasing muscle weakness and floppiness (common)
• Loss of skills such as sitting, walking, eating or speaking (common)
• Weakening of the breathing muscles (common; a breathing machine may be needed over time)
• Drooping eyelids (sometimes)
• Difficulty swallowing and speaking (sometimes)
• Hearing loss or seizures (sometimes)

How is it diagnosed?

The diagnosis is considered when there is muscle weakness and loss of skills. A small piece of muscle may be taken (muscle biopsy) to examine the mitochondrial DNA. The diagnosis is confirmed with a genetic test that shows two changes in the TK2 gene.

Treatment and care

Care is provided by a team of different specialists. In Europe and the USA there is also a specific medicine approved for this disease. Physiotherapy helps to preserve muscle function and prevent joint shortening. If feeding is difficult, a feeding tube may be used. For breathing, chest physiotherapy and, if needed, breathing support are given. The doctor who follows the disease decides which treatment is suitable.

For the family: inheritance and genetic counselling

The disease is passed on through recessive inheritance. The mother and father are usually carriers without symptoms. In each pregnancy, the chance that the baby is affected is 25%; genetic counselling is recommended.