Mitochondrial Diseases

Question 1

Mitochondria

Answer 1

• 5 functional enzyme complexes

- Complex subunits, encoded by motichondrial and nuclear DNAA

Question 2

Symptoms of mitochondrial disease

Answer 2

• Varied
• Ears: sensorineural deafness, aminoglycoside sensitivity,
• Eyes: optical atrophy, retinitis pigmentosa, cataracts
• Bones: myelodysplasia, sideroblastic anaemia, thrombocytopenia, cyclic neutropenia
• Heart: hypertrophic and dilated cardiomyopathies, conduction defects, endocardialfibroelastosis
• Kidney: proximal tubulopathy, glomerulosclerosis, nephropathy
• GIT: liver failure, chronic diarrhoea, villous atrophy, pseudo obstruction
• Head: paragangliomas, hypoparathyroidism, facial dysmorphism, hypertrichosis
• Pancreas: insulin secretion defects, exocrine dysfunction

Question 3

Prevalence of OxPhos diseases

Answer 3

• 1/6,500 births
• 1/200 carry pathogenic mtDNA mutations
• only 1/10,000 diagnosed with mtDNA diseases- more prevalent than HD

Question 4

What can be affected in a mitochondrial disease

Answer 4

• OxPhos enzyme biogenesis
• Nucleotide transport and synthesis
• Membrane composition and dynamics
• mtDNA replication and expression

Question 5

Leigh Syndrome

Answer 5

• Most common mitochondrial disease of childhood
• Typically healthy until ~6 months
• Progressive, episodic, neurodegenerative disorder
• Motor and/or intellectual regression with signs of brainstem dysfunction
• Focal symmetric spongiform lesions in CNS
• Demyelination, gliosis, capillary proliferation
• High plasma lactic acid, deaath usually by 3 years of age

Question 6

Alpers syndrome

Answer 6

• Normal at birth, mild developmental dedlay, usually by 2 years of age
• Progressive developmental regression, persistent vomitting, visual deterioration and seizures
• Seizures typically sudden onset, intractable, classically myoclonic and focal
• Liver dysfunction- often only biochemical until terminal stages
• Abnormal EEG and progressive cortical atrophy
• Primarilyu grey matter involvement, particularly grey matter involvement. Spongiosis, nerve cell loss, astrocytosis and gliosis

Question 7

Challenges with OxPhos molecular diagnosis

Answer 7

• Large number of candidate genes
• Mostly private mutations
• Common mutations in only a few genes
• Genotype/phenotype correlation often poor
• Molecular diagnosis may require sequential testing of many genes and currently needs expert guidance
• -Sensitivity and specificity of next gen sequencing for testing are still being established

Question 8

MinION

Answer 8

Third generation sequencing technology, the MinION device is a miniaturised single-molecule analysis system, smaller than a smart phone, designed for single use, to work through a USB port
Directly reads a single DNA strand through a nano pore, by measuring changes in electrical current

Question 9

Why don’t any paternal mitochondria get inherited?

Answer 9

There are 200,000 mitochondria in ovum, 50 in sperm, they work hard to swim the sperm, the mtDNA is a bit degraded- accumulation of mutations, Additionally, the fathers mitochondria are expelled.

Question 10

Diagnosis

Answer 10

• Histology

- Enzyme and mtDNA analysis- RFLP

Question 11

Reproductive options

Answer 11

• CVS or amniocentesis (prenatal testing)
• Preimplantation genetic diagnosis
• Nuclear trandfer, use donor oocyte and therefore donor mitochondria (with ICSI)
• Cytoplasmic transfer- cytoplam from donor oocyte (with ICSI)
• Donor oocyte, with fathers sperm