Hypertrophic cardiomyopathy (HCM) is defined by the presence of increased ventricular wall thickness or mass in the absence of loading conditions (hypertension, valve disease) sufficient to cause the observed abnormality.

An abrupt loss of heart function.

A slower than normal heart rate (in adults, slower than 60 beats per minute).

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

Abnormally increased size of the liver.

Forceful ejection of the contents of the stomach through the mouth by means of a series of involuntary spasmic contractions.

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

The complete absence of wakefulness and consciousness, which is evident through a lack of response to any form of external stimuli.

A type of focal-onset seizure characterized by a motor sign as its initial semiological manifestation.

A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes.

Encephalopathy is a term that means brain disease, damage, or malfunction. In general, encephalopathy is manifested by an altered mental state.

Atrophy (wasting, decrease in size of cells or tissue) affecting the cerebrum.

Underdevelopment of the corpus callosum.

A bilateral tonic-clonic seizure is a seizure defined by a tonic (bilateral increased tone, lasting seconds to minutes) and then a clonic (bilateral sustained rhythmic jerking) phase.

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Loss of developmental skills, as manifested by loss of developmental milestones.

A type of dystonia that affects all or most of the body.

A proneness to anger, i.e., a tendency to become easily bothered or annoyed.

Intellectual disability, previously referred to as mental retardation, is characterized by subnormal intellectual functioning that occurs during the developmental period. It is defined by an IQ score below 70.

An abnormally low volume of the white matter of the brain.

Head circumference below 2 standard deviations below the mean for age and gender.

Lack of breathing with no movement of the respiratory muscles and no exchange of air in the lungs. This term refers to a disposition to have recurrent episodes of apnea rather than to a single event.

Abnormal acid accumulation or depletion of base.

Body temperature elevated above the normal range.

Metabolic acidosis (MA) is characterized by a fall in blood pH due to a reduction of serum bicarbonate concentration. This can occur as a result of either the accumulation of acids (high anion gap MA) or the loss of bicarbonate from the gastrointestinal tract or the kidney (hyperchloremic MA). By definition, MA is not due to a respirary cause.

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

A reduction in the activity of the mitochondrial respiratory chain complex I, which is part of the electron transport chain in mitochondria.