Glossary

Prefixes:

• Hyper-: more than usually encountered, above normal (for example, "hyperactive" refers to a subject whose behaviour is characterized by an increased and continuous motor activity);
• Hypo-: less than usually encountered, below normal (for example, "hypotonia" refers to a decrease in the normal muscle tone).

Suffixes:

• -osis: accumulation of a given compound inside the body (for example, "acidosis" refers to an accumulation of acid substances, "lipidosis" refers to an accumulation of lipids);
• -emia: accumulation of a given substance in blood (for example,
  "hyperglycinemia" refers to an increased concentration of glycine in blood);
• -uria: accumulation of a given substance in urine (for example,
  "aminoaciduria" refers to an increased concentration of aminoacids in urine).

DEFINITIONS:

ACIDOSIS: pathologic condition characterized by an abnormal accumulation of acid substances in body fluids, mainly in blood.

ADP: Adenosine Diphosphate. High energy compound, it is formed by adenosine linked to two phosphoric acid groups. It is derived from ATP and its energetic level is lower of that of ATP.

ALPERS disease: Progressive Infantile Poliodystrophy. It may be seldom related to OXPHOS defects, including mitochondrial DNA depletion syndromes.

APHASIA: loss or impairment of language which is not related to impaired hearing (deafmutism), expressive speech problems (dysarthria) or psychogenic disorders.

ATAXIA: coordination disorder impairing the degree or direction of voluntary movements and resulting in a reduced ability to mantain body balance.

ATP: Adenosine triphosphate. High energy compound, it is the immediate source of energy for the cells. ATP is synthesized by the metabolic process of oxidative phosphorlation (OXPHOS), when ADP is linked to a third phosphoric acid group.

BARTH syndrome: disease condition characterized by cardiomyopathy, neutropenia and increased 3-methylglutaconic acid in blood and urine.

CARNITINE: Cofactor necessary to transport fatty acids inside the mitochondrion.

CNS: Central nervous System (brain and spinal cord).

COMPLEX I: NADH-Coenzyme Q reductase (respiratory chain enzyme).

COMPLEX II: Succinate dehydrogenase (respiratory chain enzyme).

COMPLEX III: Coenzyme Q-cytochrome c reductase (respiratory chain enzyme).

COMPLEX IV: Cytochrome c oxidase (COX, respiratory chain enzyme).

COMPLEX V: ATP synthase (respiratory chain enzyme).

COX: Cytochrome c oxidase (Complex IV).

CPEO: clinical syndrome characterized by Chronic Progressive External Ophthalmoplegia.

CYTOCHROME: proteins acting as electron or proton transporters within the respiratory chain. The suffix "chrome" stands for color. Cytochromes are divided in four differnt groups (a, b, c, d) basing on their ability to absorb or transmit selected colors.

CYTOPATHY: pathologic condition involving the cell or one of its components.

DEMENTIA: pathological deterioration of higher cortical functions (memory, logic thought, orientation, affection etc.).

DNA: deoxyribonucleic acid. Molecule formed by a pair of complementary strands assuming a double helical conformation, whose function is to store the information required for protein synthesis. In the human being, most DNA is contained inside the cell nucleus (nuclear DNA, nDNA). Mitochondrial DNA (mtDNA) is a much smaller molecule contained inside the mitochondrion.

mtDNA: mitochondrial DNA. It encodes for part of the respiratory chain subunits. Mitochondria are the only organelles in the cell to have their own DNA. MtDNA is maternally inherited (maternal inheritance).

nDNA: nuclear DNA. It is located inside the nucleus of the cell.

DYSKINESIAS: pathologic invulontary movements sometimes present at rest but always increased by the attempt to perform a voluntary movement and by stress; thay are usually absent during sleep. According to their distribution and frequency, they may be defined as tremor, dystonia, chorea, atethosis or myoclonus. Dyskinesias result from a dysfunction of those brain structures implied in the control of movement. Myoclonic jerks experienced while falling asleep are a benign condition.

DYSPHASIA: inability to coordinate speech in a understandable manner, due to a cerebral lesion.

ENCEPHALOPATHY: pathologic condition affecting the central nervous system. It may be congenital or acquired, ad may run a static or progressive course.

ENZYME: protein that acts by catalysing biochemical reactions. Enzymes are necessary for the normal functioning of cell metabolism.

EPILEPSY: disease condition of the cerebral cortex characterized by the occurrence of epileptic seizures. Epilepsy may be idiopathic (benign forms, usually easily controlled by specific drugs and age-related) or symptomatic (expression of a disorder of the central nervous system). Mitochondrial encephalopathies may manifest with a symptomatic epilepsy.

EPILEPTIC SEIZURES: transient clinical events that result from abnormal or excessive activity of synchronized populations of cerebral neurons. This abnormal activity results in a paroxysmal manifestation of positive (motor, sensory, psychic) or negative phenomena (loss of awareness or muscle tone) or by a mixture of the two. Myoclonic seizures: seizures marked clinically by very brief shock-like muscle contractions. Partial or focal seizures: seizures that have their onset in a neuronal population limited to one part of a cerebral hemisphere. Clinically, they may present with motor signs, somatosensory or special senses symptoms, autonomic symptoms or psychic symptoms. They may be associated with impairment of consciousness (so called complex partial seizures). Petit Mal epilepsy: epileptic syndrome in which seizures are characterized by a sudden suppression or marked decrease of consciousness, with abolition of awareness, responsiveness and memory recording (typical absences).

GENE: trait of heredity in a chromosome, controlling a particular inherited characteristic of an individual.

HEMIANOPIA: defect of one half of the visual field. It results from a lesion involving the retrochiasmatic portion of the visual pathway.

HYPOTONIA: reduced muscle tone, evaluated by assessing the degree of resistance of a given body segment to passive mobilization. Hypotonia is related to lesions in both central and peripheral nervous system.

KSS: Kearns-Sayre syndrome. Systemic mitochondrial disorder characterized by CPEO, heart conduction defects, and progressive loss of hearing. It is usually related to large deletions of mtDNA.

LACTATE or LACTIC ACID: compound overproduced when sugars are metabolized under conditions of inadequate oxygen supply. Lactate cannot be further utilized and therefore accumulates in blood and urine. Under physiolgic conditions, lactate accumulates in muscle tissue following a strenuous or prolonged exercise, leading to muscle aches and cramps. In mitochondrial disorders, lactate overprodution is related to an inadequate oxygen supply to the cells resulting from an impairment of oxidative phosphorylation.

LEIGH syndrome: Subacute Necrotizing Encephalopathy.

LHON: Leber Hereditary Optic Neuropathy.

LIC: Lethal Infantile Cardiomyopathy.

MELAS: Mitochondrial Encephalomyopathy with Lactic Acidosis and Stroke-like episodes.

MERRF: Myoclonic Epilepsy with Ragged-Red Fibers in muscle.

METABOLISM: series of enzyme-catalysed reactions necessary to produce energy from selected compounds contained in food.

MITOCHONDRIAL ENCEPHALOPATHY: pathological condition of the central nervous system resulting from an impairment of mitochondrial energy metabolism. It usually runs a progressive course.

MITOCHONDRIAL CYTOPATHY: pathologic condition of the cell related to a mitochondrial disfunction. This term is sometimes used to indicate a mitochondrial disorder.

MYOCLONUS: quick, non-rhythmic contraction of single muscles or small muscle groups, resulting in a sudden invulontary jerk of one limb. Myoclonic jerks experienced while falling asleep are a benign condition.

MYOPATHY: any pathologic condition of skeletal or heart muscle.

MITOCHONDRION: subcellular organelle present in multiple copies inside each cell. It is the site of energy production and of the cell¹s most important metabolic pathways (oxidative phosphorilation, fatty acids oxidation, pyruvate oxidation and Krebs cycle). Mitochondria are surrounded by a smooth outer membrane and by an inner membrane folded into cristae.

MNGIE syndrome: multisystem disoder characterized by Myo-Neuro-Gastro-Intestinal signs with an Encephalopathy.

NARP syndrome: pathologic condition characterized by Neuropathy, Ataxia and Retinitis Pigmentosa.

NYSTAGMUS: invulontary movement of the eyeball, characterized by altarnate slow and quick components resulting in a jerky unequal movement of the eye. It may be associated with diseases of the cerebellum and its central connections, the eye or the inner ear. In certain circumstances, it may also be produced as a normal phenomenon.

PEARSON syndrome: severe pathologic condition of the child, resulting in an impairment of bone marrow and pancreas functions. Children with Pearson syndrome sometimes develop KSS in older life.

PDH: Pyruvate dehydrogenase. Mitochondrial enzymatic complex catalysing the conversion of pyruvate into Acetyl-CoA. PDH deficiency may result in Leigh syndrome.

PHOSPHORILATION: process of linkage of a phosphoric acid group to an organic compound. Respiratory chain Complex V acts by linking a phosphoric acid group to ADP, thus forming ATP.

POINT DELETION: loss of a single nucleotide within a gene.

POINT MUTATION: substitution of a single nucleotide with a different nucleotide.

PTOSIS: drooping of the eyelid upon the eyeball, related to weakness of the muscle levator palpebrae superioris.

RESPIRATORY CHAIN: multienzymatic complex located in the inner mitochondrial membrane. It is the terminal step for the production of high energy compounds (ATP) which are necessary to mantain cell metabolism.

SYNDROME: association of signs and symptoms frequently occurring together and considered the clinical manifestation of a single disease.