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PART ONE REVISION. > GENETICS - Mutations and Defects > Flashcards

GENETICS - Mutations and Defects Flashcards

1
Q

Red-Green defects are in which disease?

A

acquired optic nerve disease (except glaucoma and autosomal dominant optic atrophy)

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2
Q

What are the main examples of trinucleotide repeat disorders? (7)

A
  1. Fragile X syndrome
  2. Friedrich’s ataxia
  3. Machado-Joseph ataxia
  4. Spinocerebellar ataxia
  5. Spinobulbar muscular atrophy
  6. Myotonic dystrophy
  7. Huntington chorea
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3
Q

Blue-yellow defects are in which disease

A

Acquired retina disease (except cone dystrophy and Stargardt’s)

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4
Q

Which mutations causes MEN 2a and MEN2b?

A

RET proto-oncogene on chromosome 10

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5
Q

What is a mutation? What external factors can cause a mutation?

A

any permanent change in DNA

1) Ionising radiation
2) Chemicals
3) UV light

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6
Q

What are the three types of point mutations?

A

1 - missense mutation - different amino acids are transcribed altering the sense of the code (haemoglobinopathies

2 - nonsense mutation - mutation leads to premature stop codon - NF type 1

3 - splice mutation - mutation alters a critical splice junction

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7
Q

What examples are there for triplet expansion diseases? What phenomenon do they cause. (4)

A

Increased number of trinucleotide repeats –> number of repeats can increase across generations, called anticipation.

  1. myotonic dystrophy (CTG repeat in DMPK gene on chromosome 19)
  2. Fragile-X (CGG repeat in FMR1 gene)
  3. Huntington’s (CAG repeat in HTT gene)
  4. Spinocerebellar ataxia (CAG expansion)
  5. Freidrech’s ataxia (GAA expansion in FXN gene)

CAG = craving glutamine
CGG = fragile, can’t grow grey matter
CTG = can’t tie genes
GAA = gaa! Ataxia awful.

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8
Q

What examples are there of microdeletion syndromes? (3)

A
  1. Prader Willi (Chromosome 15)
  2. Williams syndrome (Chromosome 7)
  3. Di George (Chromosome 22)
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9
Q

Consanguinity is more likely to have which type of inheritance?

A

Recessive

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10
Q

What is a Robertsonian translocation?

A

a chromosome rearrangement where the two long arms of two acrocentric chromosomes (non central centromeres) fuse to form a single chromosome - leading to loss of the short arms

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11
Q

How many chromosomes do robertsonian individuals have? what is their risk of trisomy in offspring?

A
  1. 45 chromosomes (normal phenotype)
  2. increased risk
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12
Q

What is lyonisation? What does it give rise to in terms of expression?

A

Lyonisation is a physiological process where one of the two X chromosomes in cells of a female is inactivated during embryonic development (male/female X chromosome is randomly affected).

gives rise to patchy expression of X-linked mutations in female carriers

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13
Q

What chromosome carries the blue pigment gene?

A

Chromosome 7

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14
Q

How does aneuploidy (abnormal numbers) occur?

A

usually in Non-disjunction during meosis I

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15
Q

How do structural changes in chromosomes occur and what is the difference between balanced and unbalanced recombination?

A

structural changes occur due to breakage followed by a recombination that is abnormal.

Balanced recombination results in chromosomes with normal amount of genetic information

Unbalanced recombination occurs when there is loss or gain of genetic material

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16
Q

What are the difference types and subtypes of balanced rearrangements? What can it do to future generations

A

Can affect future generations by increasing likelihood of producing unbalanced genes

  1. Inversions - occur when chromosome segment inverts after breaking and rejoining - can be pericentric or paracentric.
    Pericentric: Include centromere
    Paracentric: Both breaks are in same arm
  2. Translocations - exchange of segments between non-homologous chromosomes
17
Q

What is the mutation and gene implicated in Leber’s hereditary optic neuropathy?

A

Gene: MT-ND1 gene involved in synthesis of NADH dehydrogenase

Mutation: 50% is G to A nucleotide change at position 11778 in ND-4 gene

18
Q

What is a coloboma? What is the gene associated with this? Which condition is it associated with?

A

Coloboma: Failure of closure of inferonasal optic fissure

Gene: CHD7 gene found in 65% patients with CHARGE syndrome (Coloboma, heart disease, atresia choanae, retardation of growth)

19
Q

What are the main examples of mitochondrial eye disease (4)

A
  1. MELAS
  2. Leber hereditary optic neuropathy
  3. Chronic progressive external ophthalmoloplegia
  4. Neuropathy, ataxia, retinitis pigmentosa
20
Q

Why do mitochondrial diseases worsen with age?

A

REPLICATIVE SEGREGATION
Mitochondrial DNA deletions occur over time, which results in perferential replication of smaller deleted molecules –> increased number of deleted copies over time

21
Q

HEXA gene mutation is associated with what condition?

A

Tay-Sach’s syndrome

22
Q

What chromosome is implicated in NF-1
What chromosome is implicated in NF-2
What chromosome is implicated in tuberous sclerosis
What chromosome is implicatd in pseudoxanthoma elasticum?

A

NF-1 : neurofibromin on Chr 17
NF-2: merlin on Chr 22
tuberous sclerosis: TSC gene on Chr 9, 16
pseudoxanthoma elasticum: chromosome 16

23
Q

What conditions are associated with PAX2 mutation

A

Coloboma of iris
Renal aplasia.

24
Q

Which chromosome defect is associated with retinoblastoma?

A

RB1 gene on chromosome 13q.
Encodes for a tumour suppressor protein that regulates cell cycle by inhibiting transmission from G1 phase to S phase.

25
Q

Which corneal conditions have AD mutation in transforming growth factor beta 1 (TGF-1B)? Which chromosome is it on? (3)

A
  1. Reiss-Buckler’s
  2. Granular
  3. Lattice

Chromosome 5q31.

26
Q

What other ocular features are associated with aniridia?

Which systemic conditions is aniridia associated with?

A

Ocular conditions:
1. Nystagmus
2. Cataract
3. Foveal/optic nerve hypoplasia
4. Keratopathy
5. Glaucoma

Commonest variant: No associations

Systemic conditions:
1. 30-50%: Wilm’s tumour (nearby WT1 mutation)
2. Mental retardation, GUM malformations (WAGR syndrome)

27
Q

What are the ocular features of Patau syndrome?

A

Trisomy 13.

  1. Coloboma
  2. Cyclopia
  3. Persistent hyperplastic primary vitreous
28
Q

What is the main ocular feature of VHL syndrome? Which gene/ chromosome is affected?

A

VHL gene on chromosome 3

Ocular:
Retinal angiomata (capillary haemangiomata)

Non ocular:
1. Renal cell carcinoma
2. Phaeochromocytomas
3. Cerebellar haemangioblastoma.

29
Q

Which gene is associated with oculocutaneous albinism?

A

OCA2

30
Q

Which gene is associated with achromotopsia?

A

CNGA3

31
Q

Which genes is associated with infantile nystagmus

A
  1. FRMD7 mutation (idiopathic)

OCA2, PAX6, CNGA3 are also associated.

32
Q

Which genes are associated with congenital stationary night blindness? (2)

A
  1. NYX
  2. GPR179
33
Q

Which gene is associated with dominant optic atrophy?

A

OPA3

34
Q

Which condition is COL2A1 mutation associated with? What does it code for?

A

Stick to COL2 for Stickler

COL2A1 mutation is associated with Stickler syndrome – codes for type 2 collagen.

35
Q

Patients with xeroderma pigmentosa have what kind of genetic deficiency? AD or AR?

A

Nucleotide excision repair (NER) in autosomal recessive.

36
Q

ABCA4 gene is on which chromosome?

A

Chromosome 1

PART ONE REVISION. (77 decks)

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