Mitochondrial diseases

Question 1

What does the small amount of DNA in the mitochondria encode?

Answer 1

protein components of the respiratory chain and some special types of RNA

Question 2

Inheritance

Answer 2

inheritance is only via the maternal line as the sperm contributes no cytoplasm to the zygote

Question 3

How many children of an affected male will inherit the disease?
How many children of an affected female will inherit the disease?

Answer 3

None of the children of an affected male will inherit the disease

All of the children of an affected female will inherit the disease

Question 4

Histological sign on muscle biopsy

Answer 4

‘red, ragged fibres’ due to increased number of mitochondria

Question 5

What type of condition is generally caused by mitochondrial inheritance?

Answer 5

Rare neurological diseases

Question 6

Give examples of mitochondrial conditions

Answer 6

Leber’s optic atrophy

MELAS syndrome: mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes

MERRF syndrome: myoclonus epilepsy with ragged-red fibres

Kearns-Sayre syndrome

Question 7

Clinical features of Leber’s optic atrophy

Answer 7

~ age 30 years
central scotoma → loss of colour vision → rapid onset of significant visual impairment

Question 8

Clinical features of Kearns-Sayre syndrome

Answer 8

onset in patients < 20 years old
external ophthalmoplegia
retinitis pigmentosa
Ptosis may be seen
sensorineural hearing loss