Traits

Traits linked to TK2

thymidine kinase 2

The Human Phenotype Ontology links 69 traits to TK2, by body system: features seen in people with one of the gene's rare conditions.

Abnormality of the nervous system

Trait	How often it is seen
Difficulty articulating speech	Often (30–79%)
Peripheral neuropathy	Often (30–79%)
Pins and needles feeling	Often (30–79%)
Sensory axonal neuropathy	Often (30–79%)
Abnormal cerebral white matter morphology	Sometimes (5–29%)
Abnormal cerebrospinal fluid morphology	Sometimes (5–29%)
Action tremor	Sometimes (5–29%)
Ataxia	Sometimes (5–29%)
Decreased reflex response	Sometimes (5–29%)
Decreased sensation in extremities	Sometimes (5–29%)
Degeneration of cerebellum	Sometimes (5–29%)
Degeneration of cerebrum	Sometimes (5–29%)
Depression	Sometimes (5–29%)
Parkinsonism with favorable response to dopaminergic medication	Sometimes (5–29%)
Shuffled walk	Sometimes (5–29%)
Slow movements	Sometimes (5–29%)
Stooped posture	Sometimes (5–29%)
Cognitive impairment	Rarely (1–4%)
Abnormal basal ganglia morphology	Not recorded
Delayed motor skills	Not recorded
Epilepsy	Not recorded
Inability to walk	Not recorded
Intellectual disability	Not recorded
Irritability	Not recorded
Loss of ability to walk in early childhood	Not recorded

Abnormality of the musculoskeletal system

Trait	How often it is seen
Cytochrome C oxidase-negative muscle fibers	Always
Decreased lung function due to weak breathing muscles	Always
Generalized decreased muscle tone	Always
Mitochondrial myopathy	Always
Muscle degeneration	Always
Proximal neurogenic muscle weakness	Always
Ragged-red muscle fibers	Always
Muscle tissue disease	Often (30–79%)
Cogwheel rigidity	Sometimes (5–29%)
Muscle fiber degeneration	Sometimes (5–29%)
Muscle stiffness	Sometimes (5–29%)
Diffuse skeletal muscle wasting	Not recorded
EMG: myopathic abnormalities	Not recorded
Gowers sign	Not recorded
Low muscle tone	Not recorded

Abnormality of the eye

Trait	How often it is seen
Drooping upper eyelid	Always
Progressive external ophthalmoplegia	Always
Paralysis or weakness of muscles within or surrounding outer part of eye	Often (30–79%)
Color blindness	Sometimes (5–29%)
Optic atrophy	Sometimes (5–29%)
Optic neuritis	Sometimes (5–29%)
Retina issue	Sometimes (5–29%)
Visual impairment	Sometimes (5–29%)

Abnormal cellular phenotype

Trait	How often it is seen
Depletion of mitochondrial DNA in muscle tissue	Always
Decreased activity of mitochondrial ATP synthase complex	Not recorded
Decreased activity of mitochondrial complex I	Not recorded
Decreased activity of mitochondrial complex III	Not recorded
Decreased activity of mitochondrial complex IV	Not recorded

Abnormality of head or neck

Trait	How often it is seen
Bell's palsy	Often (30–79%)
Expressionless face	Often (30–79%)
Weakness of facial musculature	Often (30–79%)
Facial diplegia	Not recorded

Laboratory abnormality

Trait	How often it is seen
Elevated blood creatine phosphokinase	Always
Higher than normal levels of lactate in blood	Often (30–79%)
Abnormal urinary amino-acid findings	Not recorded
Increased lactate in body	Not recorded

Abnormality of limbs

Trait	How often it is seen
Winged shoulder blade	Often (30–79%)
Hand muscle weakness	Sometimes (5–29%)
Limb muscle weakness	Not recorded

Abnormality of the cardiovascular system

Trait	How often it is seen
Disease of the heart muscle	Often (30–79%)

Abnormality of the digestive system

Trait	How often it is seen
Poor swallowing	Always

Abnormality of the ear

Trait	How often it is seen
Hearing impairment	Sometimes (5–29%)

Abnormality of the voice

Trait	How often it is seen
Weak voice	Sometimes (5–29%)

Constitutional symptom

Trait	How often it is seen
Decreased ability to exercise	Sometimes (5–29%)

How often is among people with one of the gene's conditions, the most often across them, as the Human Phenotype Ontology records it. These pages describe traits and the research behind them; they are not a diagnosis, and a doctor or genetic counsellor is the person to ask about symptoms.

Where this comes from

The Human Phenotype Ontology, release 2026-09-01: the traits linked to TK2 and how often each is seen. Find out more at hpo.jax.org.

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