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Medical Genetics > Week 2 > Flashcards

Week 2 Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

—————- : a type of gene mutation in which the addition or deletion of one or more nucleotides causes a shift in the reading frame of the codons in the mRNA, which may lead to the alteration in the amino acid sequence at protein translation.

A

frameshift

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2
Q

Synonymous vs Non-Synonymous Substitution

A
  • Synonymous –> silent (no effect on the amino acid )
  • Non-synonymous –> Missense / nonsense (alters an amino acid which may produce a malfunctioning protein)
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3
Q

Nonsense vs missense mutation

A

Missense: substituation of a different amino acid into the amino acid sequence as a result of the nucleotide change
Nonsense: a point mutation which introduces a premature stop codon into mRNA sequence as a result of a nucleotide change.

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4
Q

what type of mutation causes Cystic Fibrosis?

A

Loss of fxn on the CFTR gene

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5
Q

what type of mutation is Duchenne muscular dytrophy (DMD) + Mode of inheritance

A

Type: out-frame mutation on the Dystrophin gene
mode : X-linked recessive (XLR)

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6
Q

Clinical presentations of Duchenne Muscular dystrophy (DMD)

A

1) Progressive muscle weakness
2) Wheelchair dependency
3) delayed motor milestones
4) cardiomyopathy

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7
Q

Clnical case

  • 3-year-old boy
  • Unable to run
  • Muscle weakness
  • Uncle died at age 21 and was on wheelchair
  • Muscle biopsy
  • Loss-of-function mutations in the Dystrophin gene (X-linked recessive)
  • Mostly deletions of part or all of the gene

Disorder?

A

DMD - Duchenne muscular Dystrophy

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8
Q

Give an example of a disease caused by an inframe mutation (Gain of function mutation )

A

Beckers muscular Dystrophy

*some Dystrophin produced

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9
Q

clinical case:
* 6-year-old girl
* Multiple fractures/ minor trauma
* Blue sclera
* Abnormal structural integrity of bones

disease?

A

Osteogenesis Imperfecta (OI type IV)

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10
Q

Osteogenesis Imperfecta are caused by Altered structures of ? what type of mutation?

A

type: Dominant negative mutations
altered sturctures: pro α1(1)/ pro α2(1) chains/ Integration into triple helix

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11
Q

Type of mutation of Type I OI

A

Nonsense mutation

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12
Q

Type of mutation of Type II-IV OI

A

Missense, dominant negative

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13
Q

what syndrome is missing chromosome 4?

A

Wolf-Hirschhorn syndrome, Huntington chorea, Achondroplasia

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14
Q

Why do people with Wolf-Hirschorn (WHS) do not develope Huntington Disease or Achondroplasia ?

A

Becasue they 4p gene is delelted at different regions

Wolf-Hirschhorn syndrome (4p-)
HD (4p16.3)
Ach- FGFR3 (4p16.3)

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15
Q

Type of mutation of Osteogenesis Imperfecta (COL1A1 vs COL1A2)

A

COL1A1–> dominant negative
COL1A2 –> loss of function

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16
Q

Clinical case:
* 4-year-old boy
* Unusual skin pigmentation- 7 Café-au-lait macules > 5mm
* spine –> mild scoliosis
* Optic glioma
* Multiple Lisch nodules (iris hamartomas)

Disroder?

A

NF1 - Neurofibromatosis Type 1

Lisch nodules

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17
Q

————- The fraction/proportion of individuals with a genotype known to cause a disease who have any signs or symptoms of the disease

  • Does not involve severity of the disease
  • Can be aged-dependent
A

Penetrance

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18
Q

MoI + type of mutation of Hereditary Breast and Ovarian cancer?

*MoI : mode of inheritance

A

MoI : Autosomal dominant inheritance (AD)
mutations in : BRCA1/2

* Reduced penetrance (Females have 87% risk , males have 20% risk)

19
Q

Reduced penetrance typically described for autosomal [dominant/recessive] diseases

A

Dominant

Note:
can also apply to recessive ones (e.g.haemochromatosis)

20
Q

Autosomal recessive disease w/ Reduced penetrance

A

Haemochromatosis

21
Q

MoI of Huntington disease

A

Autosomal dominant

22
Q

cause of Huntington disease

A

CAG trinucleotide repeat expansion in HTT gene
(ON an EXON)

23
Q

CF of Huntington disease

A

Motor:
involunary –> chorea, rigidity, dystonia
Voluntary –> Clumsines, dysarthria, visual gaze
Cognitive: global decline in cognitive abilities
Psychiatric: depression, personality changes (bioplar), psychosis

Mean age of onset: late 30’s-40’s (Anticipation is observed)

Triade of clinical findings: motor, cognitive, Psychiatric

24
Q

Normal CAG count?

A

6-26 repeats
* no risk of developing HD and no known risk to children

25
Q

Intermediate alleles of Huntingtin genes

A

27-35 CAG repeates

  • No risk for HD, but a small risk to children (more likely if paternal transmission)
26
Q

Reduced penetrance allele of HD

A

36-39 CAG repeats
* May develop HD and 50% risk to children

27
Q

Complete penetrance allele for HD

A

>40 CAG repeates
* will develop HD and a 50% risk to children

28
Q

MoI of Tuberous sclerosis

A

AD , full penetrance

29
Q

Allelic vs locus heterogeneity

A

Allelic : genetic disorder caused by many mutations in the same gene
Locus: mutations in a number of different genes

30
Q

A disease w/ marked Allelic heterogeneity

A

Cystic fibrosis (CFTR mutations)

31
Q

Diseases that exhibit Locus Heterogeneity

A

1) Tuberous sclerosis (TSC1 & TSC2)
2) Hereditary Multiple Osteochondromas (EXT1 & EXT2)
3) Non-syndromic retinitis pimentosa

32
Q

————– is the variation in the severity of a disorder in individuals who have inherited mutations in the same gene or even the same disease alleles (extent to which a genetic defect is expressed)

A

Variable expressivity

33
Q

——————- : chromosomes of a pair are inherited from same parent, instead of one being inherited from the father and the other from the mother.’

A

Uniparental Disomy (UPD)

34
Q

Isodisomy vs heterodisomy

A

Heterodisomy means that both parental homologues are present, while isodisomy refers to the presence of two copies of one parental homologue

35
Q

CF of Angelman Syndrome (‘Happy puppet’ Syndrome)

A
  • Ataxia (loss of coordination)
  • Developmental delay
  • Microcephaly
  • seizures
  • Minimal use of words
  • Behavioural: excitability , frequent laughter
  • Wide mouth (spaced out teeth)
  • Prognathism ( protruding large lower jaw)
  • light coloured skin, hair, and eyes
  • Characterisitic EEG
36
Q

Angelman Syndrome is cause by what type of mutation?

A

loss of function of maternally inherited UBE3A gene at 15q11-q13

37
Q

CF of Parder-Willi Syndrome (PWS)

A
  • Infancy -> hypotonia (flapping), Feeding difficulties
  • Later –> excessive eating, obesity
  • Developmental delay
  • Hypogonadism (reduced testosterone production)
  • Short stature
  • Bitemporal narrowing
  • Palpebral fissures (almond-shaped, slightly upslanting)
38
Q

Parder-Willi Syndrome are caused by what type of mutation?

A

Microdeletetion of Paternally inherited genes at 15q11-q13 SNPRN,NECDIN

39
Q

CF of Beckwith-Wiedmann Syndrome

A
  • Overgrowth syndrome, macrosomia (big baby)
  • Macroglossia(large tougue)
  • Hypoglycaemia (neonatal)
  • Umbilical hernia
  • Asymmetry/ hemihyperplasia
  • Embryonal tumours (Wilms, hepatoblastoma)
  • Renal anomalies
  • Ear creases/ ear pits
40
Q

Beckwith-Wiedemann Syndrome is casued by what type of Mutation?

A

MoI: paternal uniparetnal disomy (UPD)
* Mutations in 11p15.5
(or epigenetic changes at DMR1)

41
Q

Example of a Skewed X-inactivation syndrome

A

Duchenne muscular dystrophy
MoI: X-linked recessive

42
Q

Skewed X-inactivation is more common in [males/females]?

A

females
note: X-linked recessive disorderes such as Duchenne muscular dystrophy

43
Q

———————– : a process by which one of the copies of the X chromosome is inactivated in therian female mammals

A

X-chromosome inactivation

44
Q

————-: Monoallelic expression of certain genes in zygote based on parent of origin

( process by which only one copy of a gene in an individual (either from their mother or their father) is expressed, while the other copy is suppressed)

A

Genomic imprinting

Medical Genetics (8 decks)

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