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2019 FunMed PBLs > Week 2 - A Day At The Genetics Clinic > Flashcards

Week 2 - A Day At The Genetics Clinic Flashcards

1
Q

What gene is involved in Huntington’s?

A

HTT gene

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2
Q

What mode of inheritance is Huntington’s?

A

Autosomal Dominant

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3
Q

What mode of inheritance is cystic fibrosis?

A

Autosomal recessive

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4
Q

What mode of inheritance is muscular dystrophy?

A

X linked recessive

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5
Q

Which mode of inheritance requires that both copies of the same gene or alleles be the same in both heterozygous chromosomes?

A

Autosomal recessive

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6
Q

Which predominant mode of inheritance occurs in Mendelian diseases that affect mostly males

A

X linked recessive

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7
Q

What protein does the CFTR gene code for?

What is the function of this protein?

A

Cystic fibrosis transmembrane conductance regulator

Open and close chloride channels in lungs, pancreases, enterocytes which draws water into secretions

The CFTR protein is found in all membranes

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8
Q

Describe the type of mutations which affect the HTT gene and leads to the symptoms of Huntington disease

A

There is an increase in the number of CAG repeats in exon 1 of the HTT gene

10-35 repeats = pre mutation allele
36-39 repeats = variable penetrance
40+ repeats = 100% penetrance

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9
Q

How do mutations in the CFTR gene lead to the development of cystic fibrosis?

A

The CFTR gene regulates the opening and closing of chloride channels

Cl- moves along the electrochemical gradient

A faulty CFTR gene means Cl- does not move into secretion, water is not drawn into secretions and secretions are thicker and clog up the pancreas and lungs causing symptoms of cystic fibrosis (e.g. failure to thrive etc)

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10
Q

List TWO sources from which DNA samples can be obtained from an adult

A

Buccal smear (epithelial cells)

Blood sample

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11
Q

What is a trait called if it is controlled by only one gene?

A

Mendelian

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12
Q

Name some examples of autosomal dominant diseases?

A

Huntington’s disease
Marfan syndrome
Neurofibromatosis type 1
Polycystic kidney disease

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13
Q

Name some examples of autosomal recessive diseases

A 
Phenylketonuria
Tay Sachs disease
Albinism
Sickle cell disease
Glycogen storage diseases
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14
Q

Name some examples of X linked recessive diseases

A

Haemophilia A and B
Hunter syndrome
Duchenne and Becker MD

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15
Q

Which part of the brain is effected in Huntington’s?

A

Cortex

Striatum

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16
Q

Which amino acid does CAG code for?

A

Glutamine

17
Q

What are long repeats of CAG called in Huntington’s?

A

Poly-glutamines

18
Q

Where is CFTR found?

A

In the epithelial cells of many organs including the lung, liver, pancreas, digestive tract, reproductive tract and skin

19
Q

What causes the symptoms of Cystic Fibrosis?

A

CFTR is responsible for opening and closing chloride channels in the epithelial cells lining many organs including the lung, liver, pancreas, digestive tract, reproductive tract and skin

Because there is reduced chloride channels opening, secretions are thicker as water is not drawn into them, this results in clogging and the symptoms of cystic fibrosis

20
Q

What are the different mutations you can have with Cystic Fibrosis?

A

As the CFTR protein is found in many different epithelial cells, you can have mutations in different places.

The mutation you have determines the severity of the disease and the mode of action of the disease

Examples are: 
- Class I CF mutations 
No synthesis of CFRTR
Mutation: Nonsense, frameshift or splicing mutation that prevents CFTR biosynthesis) 
Genotype: G542X
  • Class II CF mutations
    Phenotype: Reduced trafficking
    Mutation: CFTR is misprocessed in the ER, leading to an absence of functional protein at the cell membrane
    Genotype: F508del
  • Class III CF mutations
    Phenotype: Reduced gating
    Mutation: CFTR protein reaches the cell membrane but once there it is unstable
    Genotype: G551D
  • Class IV CF mutations
    Phenotype: Decreased conductance
    Mutation: CFTR protein reaches the cell membrane but abnormal conformation of the pore leads to disrupted ion flow
    Genotype: R117H
  • Class V CF mutations
    Phenotype: Reduced synthesis
    Mutation: Reduced amount of CFTR protein at the cell surface due to reduced protein synthesis
    Genotype: A455E
21
Q

What is the phenotype, mutation and genotype of a Class I CF mutation?

A

Phenotype: No synthesis

Mutation: Nonsense, frame shift or splicing mutations prevent CFTR biosynthesis

Genotype: G542X

22
Q

What is the phenotype, mutation and genotype of a Class II CF mutation?

A

Phenotype: Reduced trafficking

Mutation: CFTR is misprocessed in the ER, leading to an absence of functional protein at the cell membrane

Genotype: F508del

23
Q

What is the phenotype, mutation and genotype of a Class III CF mutation?

A

Phenotype: Reduced gating

Mutation: CFTR protein reaches the cell membrane but once there is unstable

Genotype: G551D

24
Q

What is the phenotype, mutation and genotype of a Class IV CF mutation?

A

Phenotype: Decreased conductance

Mutation: CFTR protein reaches the cell membrane but abnormal conformation of the pore leads to disrupted ion flow

Genotype: R117H

25
Q

What is the phenotype, mutation and genotype of a Class V CF mutation?

A

Phenotype: Reduced synthesis

Mutation: Reduced amount of CFTR protein at the cell surface due to reduced protein synthesis

Genotype: A455E

26
Q

What are the symptoms of cystic fibrosis?

A
  • recurring chest infections
  • wheezing, coughing, shortness of breath and damage to the airways
  • difficulty putting on weight and growing
  • jaundice
  • diarrhoea, constipation or large, smelly poo
  • a bowel obstruction in newborn babies (meconium ileus) surgery May be needed

Can also develop the following related conditions:

  • diabetes
  • thin and weakened bones (osteoporosis)
  • infertility in males
  • liver problems
27
Q

Why does thick mucus cause the symptoms of cystic fibrosis?

A

The build up of sticky mucus in the lungs can cause breathing problems and increases the risk of lung infections (this can cause the lungs not to work properly over time)

Mucus can also clog up the pancreas which usually helps with digestion, this stops enzymes reaching the gut and helping with digestion

A lot of people with CF don’t absorb nutrients from food properly and need to eat more calories to avoid malnutrition

28
Q

What are the symptoms of muscular dystrophy?

A
  • sway back
  • shoulders and arms are held back awkwardly when walking
  • belly sticks out due to weak belly muscles (child is poor at sit ups)
  • weak butt muscles (hip straighteners)
  • thin, weak things (especially front part)
  • knees may bend back to take weight
  • thick lower leg muscles (the muscle is mostly fat and not strong)
  • tight heel cord (contracture) child may walk on their toes
  • poor balance: falls often (awkward clumsy if walking)
  • weak muscles in front of leg cause foot drop and tip toe contracture
29
Q

What is the age of onset of DMD?

A

2-5 years

30
Q

What is the age of onset for Becker Dystrophy?

A

Late onset

8-10 years

31
Q

Which is more common out of Duchenne’s and Becker’s?

A

Duchenne

32
Q

What is the progression like for Duchenne’s and Becker’s?

A

Duchenne: Rapid
Becker: Slow

33
Q

What is the intelligence level of patients with Duchenne’s?

A

Sub normal

34
Q

What is the intelligence level of patients with Becker’s?

A

Normal

35
Q

What is the life expectancy of someone with Duchenne’s?

A

15-20 years

36
Q

What is the life expectancy of someone with Becker’s?

A

40- 50 years

37
Q

What is a common associated symptom of Duchenne’s muscular dystrophy?

A

Cardiomyopathy

38
Q

What is a common associated problem of Becker’s Dystrophy?

A

Colour Blindness

2019 FunMed PBLs (8 decks)

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