Mitochondrial Disease & 3‑Parent IVF

Mitochondrial disease definition

Disorders caused by impaired mitochondrial function

Mitochondrial disease symptom range

Symptoms vary widely; can be late onset

Mitochondrial disease common symptoms

Extreme tiredness, heart problems, diabetes, mobility/balance difficulties, deafness, epilepsy

Mitochondrial disease severity

Depends on ratio of faulty mitochondria to healthy mitochondria

Mitochondrial disease rarity

Considered rare

Mitochondrial disease genetic origin

Can be caused by mutations in nuclear DNA or mitochondrial DNA

mtDNA inheritance

Inherited exclusively through maternal line

Maternal inheritance rule

Only females pass mtDNA to next generation

Affected males mtDNA transmission

Affected males do NOT transmit mtDNA mutations

POLG gene location

Encoded in nuclear DNA

POLG exception

POLG‑related mitochondrial disease does NOT follow maternal inheritance

Mitochondrial disease siblings

Siblings may vary in severity due to heteroplasmy

Heteroplasmy definition

Presence of mixed populations of normal and mutant mtDNA within a cell

Heteroplasmy effect

Higher mutant load → more severe disease

Threshold effect

Symptoms appear when mutant mtDNA exceeds functional threshold

Mitochondrial bottleneck

Random segregation of mtDNA during oogenesis affects offspring mutant load

Tissues most affected

High‑energy tissues: muscle, heart, brain, endocrine organs

Mitochondrial disease diagnosis

Often requires genetic testing, muscle biopsy, metabolic studies

Mitochondrial disease biochemical hallmark

Defects in oxidative phosphorylation

OXPHOS impairment

Reduced ATP production; increased lactate

Mitochondrial disease metabolic sign

Lactic acidosis due to reliance on anaerobic glycolysis

Mitochondrial disease organ involvement

Multisystemic; can affect any organ

Mitochondrial disease variability

High variability even within families

Mitochondrial disease inheritance pattern

Maternal for mtDNA; Mendelian for nuclear DNA mutations

Three‑parent IVF definition

Mitochondrial replacement therapy using donor mitochondria

Three‑parent IVF purpose

Prevent transmission of pathogenic mtDNA mutations

Three‑parent IVF method

Nuclear DNA from mother transferred into donor egg with healthy mitochondria

Three‑parent IVF embryo genetics

Nuclear DNA from mother and father; mtDNA from donor

Three‑parent IVF ethical concerns

Genetic modification, germline changes, regulatory issues

Three‑parent IVF alternative name

Mitochondrial replacement therapy (MRT)

Three‑parent IVF target

Women with pathogenic mtDNA mutations

Three‑parent IVF benefit

Allows birth of genetically related child without mtDNA disease

Three‑parent IVF limitation

Does not treat nuclear‑encoded mitochondrial disorders

Three‑parent IVF risk

Carryover of small amounts of mutant mtDNA

Three‑parent IVF regulatory status

Approved in UK; restricted in many countries

Mitochondrial replacement therapy techniques

Spindle transfer, pronuclear transfer

Spindle transfer

Mother’s nuclear DNA spindle transferred into donor oocyte before fertilization

Pronuclear transfer

Pronuclei transferred after fertilization into donor zygote with healthy mitochondria

Mitochondrial disease hallmark histology

Ragged red fibers in muscle biopsy

Ragged red fibers cause

Accumulation of abnormal mitochondria in muscle fibers

Mitochondrial disease biochemical tests

Lactate, pyruvate, amino acids, organic acids

Mitochondrial disease imaging

May show basal ganglia lesions, stroke‑like episodes

Mitochondrial disease common syndromes

MELAS, MERRF, LHON, Leigh syndrome

MELAS acronym

Mitochondrial Encephalomyopathy, Lactic Acidosis, Stroke‑like episodes

MERRF acronym

Myoclonic Epilepsy with Ragged Red Fibers

LHON acronym

Leber Hereditary Optic Neuropathy

Leigh syndrome

Severe neurodegenerative disorder of infancy; defects in OXPHOS

mtDNA mutation types

Point mutations, deletions, duplications

Nuclear mitochondrial gene examples

POLG, TWNK, NDUFS genes

POLG function

Mitochondrial DNA polymerase gamma

POLG mutation effects

mtDNA depletion, multiple deletions, neurological disease

Mitochondrial disease treatment

Supportive; no cure

Mitochondrial disease supplements

CoQ10, riboflavin, L‑carnitine (variable benefit)

Mitochondrial disease management

Multidisciplinary; symptom‑based

Mitochondrial disease prognosis

Highly variable; depends on mutation and heteroplasmy