Learn The BasicsThe main signs and symptoms of Thymidine Kinase 2 deficiency (TK2d) include progressive weakness affecting the muscles in the arms and legs, as well as those used for swallowing and breathing.
Patients may also show other signs and symptoms according to the type of disease, which is based on the age of symptom onset.
Loss of motor skills
The muscle weakness that affects the arms and legs causes patients with TK2d to lose their fine and gross motor skills over time, as the disease progresses.
In its most severe form, TK2d affects infants before age 1. These babies have low muscle tone throughout their bodies and usually never learn to walk. Those who do learn to walk usually lose this ability soon after they begin.
Patients with childhood-onset TK2d (between ages 1 and 12), which is less severe and progresses more slowly, may walk independently for a few years but usually require a wheelchair for mobility by the time they are age 10. They may also experience feeding difficulties, failure to thrive, and early respiratory insufficiency.
Muscle weakness in the limbs appears later in patients with late-onset TK2d, symptoms of which usually appear after age 12. This muscle weakness mainly affects the shoulders, arms, hips and thighs, known as proximal muscles, or those closest to the trunk. The weakness in the shoulder muscles can cause the shoulder blades to stick out, also known as scapular winging.
Even though the muscle weakness worsens with time, some patients with late-onset TK2d maintain the ability to walk, though they may need assistive devices such as a cane or a walker as the disease progresses.
Feeding difficulties
The weakness affecting the muscles used for chewing and swallowing can lead to feeding difficulties in patients with TK2d. This can increase the risk of aspiration, or accidentally inhaling food into the airways and choking.
A nasogastric tube or gastrostomy tube may be needed in such cases to ensure patients receive all the nutrients that they require.
A nasogastric tube is a thin plastic tube that is inserted into one of the nostrils and goes from the back of the throat through to the stomach, while a gastrostomy tube is a device that is placed surgically onto the abdomen to provide direct access to the stomach. In both cases, food can reach the stomach without the need to be chewed or swallowed, as can liquids and medication.
Breathing problems
One of the most serious and dangerous symptoms of TK2d is muscle weakness affecting those used for breathing.
Most patients with the disease eventually require a ventilator for breathing. This can be either non-invasive or invasive.
Respiratory failure is the most common cause of death in TK2d.
Other signs and symptoms
Other signs and symptoms of TK2d may include difficulty or inability to move the eyes (known as progressive external ophthalmoparesis) and droopy eyelids or ptosis due to muscle weakness affecting the muscles of the face. Patients may also experience hearing loss, and those with infantile-onset TK2d are at risk for heart problems, kidney problems, epilepsy and multiple bone fractures.