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POM (Principles of Medicine) (RF) > Genetic disorders > Flashcards

Genetic disorders Flashcards

1
Q

What are the main points for using a genetic pedigree?

A

Provides a clear simple summary of information
Able to spot patterns easily
Explain pattern to patient
Calculate the risk of passing on disease or being a carrier
Allows informed choice

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2
Q

How are generations denoted on genetic pedigree?

A

Using roman numerals

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3
Q

How are offspring birth ordered traditionally on genetic pedigrees?

A

Left tor right, individuals denote by Arabic numerals.

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4
Q

Conventionally, which side is paternal lineage and maternal lineage denoted on a genetic pedigree?

A

Paternal - right

Maternal - left

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5
Q

In relation to the proband which % of DNA is shared between grandparents?

A

25%

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6
Q

In relation to the proband, which % of DNA is shared between parents?

A

50%

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7
Q

In relation to the proband, which % of DNA is shared between siblings?

A

50%

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8
Q

In relation to the proband, which % of DNA is shared between Aunts & uncles?

A

25%

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9
Q

In relation to the proband, which % of DNA is shared between 1st degree cousins?

A

12.5%

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10
Q

What is classified as consanguineous mating?

A

Mating occurs if 2nd cousins or closer (3.13% shared DNA)

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11
Q

What pattern is provided by autosomal dominant conditions on a genetic pedigree?

A

Vertical transmission
The tendency for not all offspring expressing the conditions
Both genders are affected
Minimum of one parent required.

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12
Q

Why are some familial disorders not expressed within the pedigree?

A

Have an age of onset, developing with age due to an accumulation of sporadic mutations
Decreased patients may not develop the disease, thus not expressed within the pedigree

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13
Q

Which trinucleotide repeat causes Huntington’s?

A

CAG

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14
Q

What inheritance pattern is demonstrated by Huntington’s?

A

Monogenic autosomal dominant disorder

Unstable mutation confers for a variable number of repeats

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15
Q

How many CAG repeats cause full penetrance?

A

40+

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16
Q

Why is the Huntingtin gene unstable?

A

Instability increases over successive generations. CAG is a codon for gutamine, series of repeats results in the production of glutamine chain -Polyglutamine tract/Poly-Q tract
Accumulation of HTT within neurones results in neuronal death
Age of onset decreases with severity and number of repeats

17
Q

What type of gene is MEN1?

A

Tumor suppressor
Affected individuals have one mutation in one allele, over a period of time, second version is mutated, thus there is no active version

18
Q

The development of a second mutation within the MEN1 gene causes what?

A

Leads to the development of benign adenomas

19
Q

How is mitochondrial inheritance conferred?

A

The mutated gene is present in the mitochondrial DNA of the ovum; subsequent.y mtDNA is exclusively inherited from maternal lineages

20
Q

Which lineage has a strong inheritance pattern of mitochondrial DNA?

A

Maternal lineage

21
Q

What type of transmission pattern is evident for mitochondrial DNA inheritance?

A

Vertical transmission

Affects all generations,both genders are affected since the mutated gene is inherited from the mother

22
Q

What are the complicating factors of mitochondrial inheritance in terms of genomes and mt number?

A

Have multiple copies of genome ,therefore a proportion express normal genotype and mutant genotype
Offspring inherit varying numbers of mutated mitochondria this can change with time

23
Q

What is the pattern of inherited mitochondrial disease and age? Explain

A

Diseases develop with age due to accumulation of mutated mitochondria

24
Q

How do mitochondria replicate?

A

Binary fission

25
Q

What is the definition of genetic risk?

A

Risk is the calculation of the predicted chance of having the disease or being a carrier
Risk can only be calculated based upon the known phenotype to subject
Multiplication of risks to calculate overall risk of inheriting genetic disorder

26
Q

What are risk modifiers in terms of phenotypic advantage?

A

The lineages of the disease prevalence (maternal or paternal); X-linked and mitochondrial inheritance patterns
Ethnic background: Diseases have different prevalence in different populations
Example: CF, Sickle cell, Tay-Sachs
Whereby the heterozygous express a phenotypic advantage within the environment, the allelic frequency would increase within areas of relatively higher selection pressure
Founder effect

27
Q

What is the founder effect?

A

Due to a genetic bottleneck, also produced sub-populations with increased prevalence

28
Q

Which inheritance pattern is demonstrated by hereditary hemochromatosis?

A

Autosomal recessive disorder

29
Q

Which protein is the hereditary hemochromatosis allele affecting?

A

Homeostatic iron regulatory protein (HFE)

30
Q

What effect happens due to dysfunctional HFE protein?

A

Excess iron absorption

31
Q

Where is the HFE protein located?

A

Cell surface membrane of hepatocytes

32
Q

Which receptor is the HFE protein associated with?

A

Transferrin receptor i

33
Q

Which plasma protein is bound to transferrin receptor 1?

A

Transferrin

34
Q

How does the HFE protein regulate iron levels?

A

Iron enters hepatocytes, HFE protein regulates iron absorption by preventing transferring from binding to transferrin 1
Regulates the production of hepcidin, Hepcidin determiens level of iron absorbed from the diet and released from storage sites within the body
HFE protein not bound to transferring receptor i ,binds to hepcidin
Formation of complex triggers production of hepcidin - inactivated when bound to TF1

35
Q

How does the HFE gene cause hereditary hemochromatosis?

A

Mutation results in excess iron absorption
Humans cannot excrete excess iron, thus accumulates in tissues
HFE dysfunction results increased absorption of transferrin

36
Q

What is the prevalence of hereditary hemochromatosis?

A

1 in 200 homozygous , 0.5%
10% of these have clinically relevant iron accumulation
0.05% have chronic tiredness fatigue - 7% main symtpom in primary care patients]Therefore 1 in 140 have hH in tiredness group

POM (Principles of Medicine) (RF) (34 decks)

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