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MTM > Single Gene Disorders > Flashcards

Single Gene Disorders Flashcards

1
Q

What are the classifications of genetic disorders

A

Single gene disorders
Multi factorial diseases
Chromosome disorders
Mitochondrial disorders
Somatic mutations

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2
Q

What are single gene mutations

A

Mutations in single genes often causing loss in function
Leads directly to disease

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3
Q

Types of single gene disorders

A

Dominant - heterozygotes with one copy of the altered genes

Recessive - homozygotes wit two copies of altered gene

X linked recessive - males with one copy of altered gene on X chromosome

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4
Q

Exceptions to Mendels rules in autosomal dominant inheritance

A

Variance in expression
Penetrance
New mutations
Anticipation

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5
Q

What do majority of mutations in autosomal dominant disorders cause?

A

Loss of function of the allele

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6
Q

Dominant disorders cause cell to cope with half of the amount of gene product. Examples of this:

A

50% Structural protein/ receptor clinical effect
50% enzyme - body can cope so no clinical effect

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7
Q

What is Marfans syndrome?

A

Autosomal dominant condition
Affects skeletal system, heart and eyes
Caused by fibrillins gene on chromosome 15

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8
Q

How can there be diagnosis using DNA

A

Allows determination of sequence/ copy number variant
Determines whether normal variant or pathogenic (harmful)

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9
Q

What is genotype-phenotype analysis

A

Sequencing of affected family member to confirm the mutation

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10
Q

What is polymorphism

A

the presence of two or more variant forms of a specific DNA sequence that can occur among different individuals or populations

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11
Q

How to determine whether a mutation is cause of disease in a family and not just polymorphism

A

Segregation studies - see whether family members that are clinically affected have same mutation

Genetic testing - see if member with mutation will develop disease

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12
Q

Clinical effects of neurofibromatosis

A

Skin cafe au last patches
Multiple neurofibroma

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13
Q

Example of a disease with variation of expression

A

Neurofibromatosis type 1
Exception of Mendels rules of autosomal dominance
Family members have different signs of the same disease
Cant predict severity of the disease

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14
Q

What disease demonstrates age related penetrance

A

Huntingtons disease
Breast cancer BRCA1

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15
Q

Is NF1 completely penetrant

A

Yes
If individual has affected gene NF1 always expressed

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16
Q

What is Huntington’s disease

A

Progressive neurological disorder
Involuntary movements
Dementia
Psychiatric disturbance

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17
Q

What is age dependant penetrance

A

Delay in onset of a genetic disease
The older they are without signs the less likely they are to develop disease

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18
Q

What is incomplete penetrance

A

Not everyone who has gene will develop disease e.g. some cancers

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19
Q

What is Achondroplasia

A

New mutation that causes the disorder in 80% patients

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20
Q

Which disease are new mutations increase with paternal age

A

Marfan
Achondroplasia

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21
Q

How does a chance of new mutation increase with paternal age

A

Higher mutation rates in males are likely to be related to greater number of germ cell divisions

22
Q

What is myotonic dystrophy

A

Autosomal dominant
Muscle weakness
Impaired muscle contraction after relaxation (myotonia)
Usual age of onset 20s-30s

23
Q

What is anticipation

A
  • In successive generations age of onset is reduced and/ or severity of the phenotype is increased
  • Unstable & expanding trinucleotide repeat mutation
  • Severity/ age of onset may correlate with number of repeats
24
Q

What is an example of anticipation

A

Myotonic dystrophy
Huntingtons

(Disorders of the nervous system)

25
Q

Examples of intragenic triplet repeats causing dominant disease

A

Myotonic dystrophy - CTG
Huntington disease - CAG

26
Q

What is an intragenic triplet repeat disorders

A

Number of triplet repeats above the upper normal limit cause the disease

27
Q

What is the usual gene repeats for huntingtons disease?

A

11-34 CAG repeats = 11-34 glutamine residues in protein
Above 34 glutamine residues causes progressive cell death

28
Q

Anticipation in Huntingtons disease:

A

Runs of more than 34 CAG repeats in HD gene expand further (during male meiosis) causing earlier age of onset in children of men with HD allele

29
Q

What is mosaicism?

A

Mutation after fertilisation
Present in somatic/ germline cells

30
Q

What is osteogenesis imperfecta

A

Brittle bone disease
Severe cond. not inherited because baby dies

31
Q

What causes osteogenesis imperfecta

A

Father has mutation in gonads
Patch of Gonadal stem cells with gene mutuion arisen from error in cell while gonad was being populated
Gamete has effected genes

32
Q

How to recognise autosomal recessive disease from pedigree

A

Cant follow disease through pedigree
See siblings affected - horizontal transmission
Equal incidence of males and females
May be evidence of consanguinity (parents have common ancestor)

33
Q

What is consanguinity?

A

Parents have shared common ancestor
Doesn’t cause genetic condition but increases likelihood of parents being carriers of autosomal recessive condition in family

34
Q

What is X linked recessive inheritance

A

One copy of an altered gene on the X chromosome
Causes disease in males
Cause females to be carriers

35
Q

The results for offspring if mother is a carrier of X linked and father unaffected

A

Unaffected daughter
Carrier daughter
Unaffected son
Affected son

36
Q

Available options for mother who is carrier of x linked disease

A

Postpone pregnancy
No further pregnancies - adoption
Further pregnancies - accept risk, prenatal diagnosis if available, egg donation, preimplantation diagnosis if available

37
Q

What is an example of x linked disease

A

Duchenne muscular dystrophy
Progressive muscle weakness (cardiac and respiratory)
Decreases life span

38
Q

How may female carriers of X linked disease be affected

A

Can show mild symptoms of X linked disease
- mild muscle aches and pain
- myalgia
- cardiac muscle abnormalities

39
Q

What causes females to show X linked recessive traits

A

Skewed X inactivation
Turner syndrome
Homozygous for a recessive trait - carry X linked mutation on both X chromosomes
X autosome translocations

40
Q

What is skewed X inactivation

A

Random X inactivation in female embryo
Should be equal paternal and maternal X
But data can become skewed and more mutated X present which causes mild symptoms

41
Q

Results for offspring if father is affected with X linked recessive inheritance but mother unaffected

A

All daughters Unaffected carriers
All sons Unaffected

42
Q

What does the pedigree for X linked dominant disease look like

A

Similar to autosomal dominance
But excess of affected females
No male to male transmission (sons inherit X from mother)
Uncommon diseases

43
Q

How many DNA bases and genes in mitochondria

A

16,600 DNA bases
37 genes

44
Q

What is mitochondrial inheritance

A

Exclusively maternal inheritance

45
Q

Description of maternal pedigree

A

May think its autosomal dominance
All offspring of affected mother will have condition
Males don’t pass on condition - sperm don’t mass on mitochondrial genes

46
Q

The number of mitochondria in egg cells

A

100,000

47
Q

The number of mitochondria in sperm cells

A

100

48
Q

The number of genes and DNA bases in nucleus

A

3,200 million DNA bases
24 chromosomes

49
Q

Examples of mitochondrial DNA disorders

A

Kearns-Sayre syndrome
MELAS

50
Q

Mode of Inheritance of haemophilia

A

X linked recessive

MTM (12 decks)

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