Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm.

Abnormally increased size of the liver.

Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it.

Absence of neurologic reflexes such as the knee-jerk reaction.

Reduction of neurologic reflexes such as the knee-jerk reaction.

Reduced strength of muscles.

A type of myopathy associated with mitochondrial disease and characterized by findings on biopsy such as ragged red muscle fibers.

Decreased strength of the neck musculature.

The presence of an increased amount of muscle fibers with an increased diameter. This feature can be ascertained by microscopic examination of a muscle biopsy sample. Together with fiber size variation and atrophied muscle fibers, and hypertrophied muscle fibers are commonly found in myopathies.

Facial nerve palsy is a dysfunction of cranial nerve VII (the facial nerve) that results in inability to control facial muscles on the affected side with weakness of the muscles of facial expression and eye closure. This can either be present in unilateral or bilateral form.

Generalized muscular hypotonia (abnormally low muscle tone).

An abnormal appearance of muscle fibers observed on muscle biopsy. Ragged red fibers can be visualized with Gomori trichrome staining as irregular and intensely red subsarcolemmal zones, whereas the normal myofibrils are green. The margins of affect fibers appear red and ragged. The ragged-red is due to the accumulation of abnormal mitochondria below the plasma membrane of the muscle fiber, leading to the appearance of a red rim and speckled sarcoplasm.

An abnormally reduced activity of the enzyme cytochrome C oxidase in muscle tissue.

An abnormal buildup of lactic acid in the body, leading to acidification of the blood and other bodily fluids.

An elevation of the level of the enzyme creatine kinase (also known as creatine phosphokinase (CK; EC 2.7.3.2) in the blood. CK levels can be elevated in a number of clinical disorders such as myocardial infarction, rhabdomyolysis, and muscular dystrophy.

Abnormally increased level of blood lactate (2-hydroxypropanoic acid). Lactate is produced from pyruvate by lactate dehydrogenase during normal metabolism. The terms lactate and lactic acid are often used interchangeably but lactate (the component measured in blood) is strictly a weak base whereas lactic acid is the corresponding acid. Lactic acidosis is often used clinically to describe elevated lactate but should be reserved for cases where there is a corresponding acidosis (pH below 7.35).

An abnormal accumulation of lipids in skeletal muscle.

An increased concentration of pyruvate in the blood.

An increased amount of glycogen in muscle tissue.

Concentration of carnitine in the blood circulation below the lower limit of normal.

Increased length and width of the tongue.

A facial appearance characteristic of myopathic conditions. The face appears expressionless with sunken cheeks, bilateral ptosis, and inability to elevate the corners of the mouth, due to muscle weakness.