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Genetics > Mitochondrial Disorders > Flashcards

Mitochondrial Disorders Flashcards

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1
Q

What is the mnemonic of mitochondrial disorders?

A

LUMP

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2
Q

What are the mitochondrial diseases?

A

L = Leber’s optic atrophy (= LHON: Leber’s hereditary optic neuropathy)

Leigh syndrome

U = Usher’s syndrome

M = MELAS syndrome

MERRF syndrome

Mitochondrially inherited: Diabetes mellitus, and Deafness

P = Pearson syndrome

Progressive external ophthalmoplegia: Kearns-Sayre syndrome

Progressive neurodegenrative disease: NARP syndrome

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3
Q

Apart from nucleus, where else is the DNA located?

A

Mitochondria

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4
Q

Are Mitochondrial DNAs single stranded or double-stranded?

A

Double stranded

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5
Q

How does mitochondrial genes differ from nuclear genes?

A
  • Mitochondrial genes have NO introns
  • They encode some different amino acid codon
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6
Q

What are the functions of mitochondrial DNA?

A

To encode >>

  • Respiratory chain enzyme subunits (protein components)
  • Transfer RNAs (tRNAs)
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7
Q

Who can transmit the disease? father/mother?

A

Mother

(inheritence is only via maternal line)

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8
Q

Why is the inheritence of mitochondrial diseases only via maternal line?

A

because, mitochondria is present in cytoplasm

& sperm do NOT contribute any cytoplasm to the zygote

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9
Q

Type & Amount of genome in the cytoplasm of ovum (that is contributed to zygote)

A

Circular genome

16.5kilobase (kb)

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10
Q

What is heteroplasmy?

A

Within cells/tissues >>> mixed population of normal and abnormal mitochondria

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11
Q

Which type of genetic disorders does show heteroplasmy?

A

Mitochondrial disorders

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12
Q

What is threshold effect?

A

Different proportion of abnormal mitochondria may be required to cause disease in different tissues

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13
Q

If a male or female is affected with a mitochondrial disease, what is his/her family history?

A

Mother surely has the disease.

Father is not affected/not predictable.

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14
Q

If father is affected, what are the chances among children?

A

NONE of the children will be affected.

(presumed: mother is normal)

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15
Q

Can an affected father transmit the disease to his his children?

A

NO.

No transmission from father.

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16
Q

Which genetic inheritences have no male-to-male transmission?

A

X-linked dominant

X-linked recessive

Mitochondrial disorders

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17
Q

Which genetic inheritences have no male-to-female transmission?

A

Mitochondrial disorders

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18
Q

If mother is affected, what are the chances among children to inherit the disease?

A

All children will inherit the disease (sons/daughters all)

(father is normal/affected does not matter)

19
Q

Which systems are involved commonly?

A

Muscles (Myopathy), brain (neurological diseases), eye (retinitis pigmentosa), heart, GIT

20
Q

How is the correlation between genotype and phenotype in mitochondrial disorders?

A

Poor

21
Q

Result of muscle biopsy in mitochondrial diseases

A

Histology: classical ‘red-ragged fibres’

(more in MERRF syndrome)

22
Q

What do ‘red-ragged fibers’ indicate?

A

Increased number of mitochondria

23
Q

Which nature of an organ is affected by mitochondrial diseases?

A

Organs that are highly dependant upon oxidative metabolism (e.g. muscles)

24
Q

What is LHON?

A

Leber’s hereditary optic neuropathy

(AKA Leber’s optic atrophy)

25
Q

What is the underlying pathology of LHON/Leber’s optic atrophy?

A

Degeneration of retinal ganglion cells (RGCs)

26
Q

What is the first presentation of LHON/Leber’s optic atrophy?

A

Sudden blurring/cloudiness of central vision

(one/both eyes)

27
Q

What is Leigh disease?

A

1. Subacute necrotising encephalopathy

2. Retinitis pigmentosa

2. Psychomotor regression:

  • Cognitive impairment
  • Ataxia
  • Weakness

Commonly death within 2-3years due to respiratory failure

28
Q

What is Usher’s syndrome?

A

Sensorineural deafness (non-progressive partial/total)

+

vision loss (due to retinitis pigmentosa) (worsen over time)

29
Q

What is MELAS syndrome?

A

ME = Mitochondrial encephalomyopathy

LA = Lactic acidosis

S = Stroke like episodes

(also myopathy)

30
Q

What is MERRF?

A

Myoclonus Epilepsy with Red Ragged Fibres

31
Q

Can diabetes mellitus be mitochondrial disorder?

A

Yes, there are some mitochondrially inherited diabetes mellitus

32
Q

What are the features of Pearson syndrome?

A

Sideroblastic anaemia +

Exocrine pancreatic dysfunction

33
Q

What is the prognosis of Pearson syndrome?

A

Most are fatal in infancy

34
Q

If Pearson syndrome survive to adulthood >>> what happens?

A

they develop Kearns-Sayre syndrome

35
Q

What is the age of onset for Kearns-Sayre syndrome?

A

<20years

36
Q

What is the triad of Kearns-sayre syndrome?

A

External ophththalmoplegia

Retinitis pigmentosa

Heart block

37
Q

What is external ophththalmoplegia?

A

weakness of eye muscles (ocular myopathy)

38
Q

What are the features of external ophthalmoplegia in Kearns-Sayre?

A

Ptosis

Symmetrical loss of eye movements (side to side mainly)

(so, usually no diplopia)

39
Q

What are the features of retina in Kearns-Sayre?

A

Retinitis pigmentosa

Night blindless

40
Q

What are the features of heart in Kearns-Sayre?

A

Cardiomyopathy

Heart block

Syncope

Heart failure

41
Q

What are the features of ear in Kearns-Sayre syndrome?

A

deafness

vestibular function loss/loss of balance

42
Q

What are the CNS features of Kearns-Sayre syndrome?

A

dementia

raised protein in CSF

sometimes:

seizures, tremor, stroke before 40years

43
Q

What are the overall common features of Kearns-Sayre syndrome?

A

Triad:

  1. External ophththalmoplegia
  2. Retinitis pigmentosa
  3. Heart block

Eye features:

  1. external ophthalmoplegia (ptosis, side-to side loss of eye movement)
  2. Retinitis pigmentosa
  3. Night blindness

Heart features:

  1. Cardiomyopathy
  2. Heart block
  3. syncope
  4. Heart failure

Ear features:

  1. deafness
  2. vestibular function loss (loss of balance)

CNS features:

  1. dementia
  2. raised protein in CSF
  3. seizure, tremor
  4. maybe, stroke <40years

Others:

symptoms releated smooth/skeletal muscle myopathies in different organs

44
Q

What is NARP?

A

Neuropathy

Ataxia

Retinitis Pigmentosa

Progressive neurodegenrative disorder

Genetics (28 decks)

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