What is TK2d?

Thymidine kinase 2 deficiency (TK2d) is a mitochondrial disease

Mitochondrial diseases are the result of genetic mutations that impact the mitochondria.

Mitochondria are responsible for making energy that the body’s organs need to function properly.

Some mitochondrial diseases are called mitochondrial myopathies, which means that they mainly affect the muscles. TK2d is a mitochondrial myopathy, and muscle weakness is the main symptom. It can show up as fatigue, trouble eating or breathing, and difficulty with motor skills like walking.

TK2d symptoms may vary, and not every person will experience every symptom. Possible symptoms include:

Low muscle tone (called floppy baby syndrome in infants), delay or loss of milestones like sitting up and walking, facial weakness, and eyelid drooping

Trouble breathing that can be severe

Trouble chewing and swallowing

Some people experience seizures and other neurological symptoms

What causes TK2d?

TK2d is caused by a genetic mutation. This mutation stops an enzyme called TK2 from working properly. This prevents the mitochondria from producing enough energy to power the body.  

The result is weakness that gets worse over time in the muscles, including those needed to walk, eat, and breathe. TK2d symptoms can start at any point in life.

Symptom onset at 12 years old or younger is considered early-onset TK2d.

It is possible that you or your loved one developed symptoms as an infant or child but didn’t get diagnosed until after age 12.

This is still early-onset TK2d.

If you or a family member has been diagnosed with TK2d, then direct relatives (like siblings) may also carry the mutated gene or have TK2d. Genetic testing can detect these mutations.

KYGEVVI is thought to restore mitochondrial DNA affected by TK2d

See the intended mechanism of action of KYGEVVI.

INDICATION

KYGEVVI is a prescription medicine used for the treatment of thymidine kinase 2 deficiency (TK2d) in adults and children with a symptom onset on or before 12 years of age.

IMPORTANT SAFETY INFORMATION

KYGEVVI may cause serious side effects including elevated liver enzyme levels. Increased liver enzyme levels in your blood are common with KYGEVVI. Your healthcare provider will do blood tests to check your liver enzyme levels before starting treatment and during treatment with KYGEVVI.

Tell your healthcare provider right away if you develop any signs or symptoms of liver problems, including loss of appetite, pain on the right side of your stomach area, dark or amber-colored urine, yellowing of your skin or the white part of your eyes, nausea and vomiting, or itching.

KYGEVVI may cause stomach and intestinal (gastrointestinal) problems. Diarrhea and vomiting are common with KYGEVVI, but may also be severe and lead to hospitalization. Tell your healthcare provider right away if you have diarrhea or vomiting during treatment with KYGEVVI that lasts longer than a few days.

The most common side effects of KYGEVVI include diarrhea, stomach area (abdominal) pain including pain in the upper stomach area, vomiting, and increased liver enzyme levels in your blood.

Your healthcare provider may change your dose, temporarily stop, or permanently stop treatment with KYGEVVI if you develop certain side effects.

Before taking or giving KYGEVVI, tell your healthcare provider about all of your medical conditions, including if you have or have had liver problems. In addition, tell your healthcare provider if you are pregnant or plan to become pregnant. It is not known if KYGEVVI will harm your unborn baby. Also, tell your healthcare provider if you are breastfeeding or plan to breastfeed. It is not known if KYGEVVI passes into your breast milk. Talk to your healthcare provider about the best way to feed your baby if you take KYGEVVI. Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements.

These are not all of the possible side effects of KYGEVVI. Call your doctor for medical advice about side effects. You are encouraged to report negative side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch or call 1-800-FDA-1088. You may also report side effects to UCB, Inc. at UCBCares® (1-844-599-CARE [2273]).

Please see additional information in the Patient Information Leaflet.