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IMS > SINGLE GENE DISORDERS > Flashcards

SINGLE GENE DISORDERS Flashcards

1
Q

what is an elctropherogram?

A

e

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2
Q

what are point mutations that cause disease?

A

Substitutions (missense)
Nonsense mutations
Insertion mutations
Deletion mutations

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3
Q

what mutation is sickle cell anaemia caused by?

A

β-globin gene

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4
Q

what is the β-globin gene lead to in sickle cell anaemia?

A

leads to a glutamic acid (E) being replaced by a valine (V) instead at position 6 in the protein
E6V

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5
Q

give an example of substitution (missense) mutation?

A

sickle cell anaemia

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6
Q

give an example of nonsense mutation?

A

Duchenne muscular dystrophy

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7
Q

what mutation is Duchenne muscular dystrophy caused by?

A

by nonsense mutations in dystrophin gene

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8
Q

what is the mutations in dystrophin gene cause in Duchenne muscular dystrophy?

A

Lysine (K) > unknown/unspecified (X) i.e. stop codon

K1524X

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9
Q

give an example of Insertion mutations?

A

Familial Hypercholesterolemia (FH)

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10
Q

what does Familial Hypercholesterolemia (FH) result in?

A

elevated levels of blood lipid

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11
Q

what mutation causes Familial Hypercholesterolemia (FH)?

A

mutation in exon 17 of the LDLR gene

c.2416_2417InsG

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12
Q

what does the c. stand for in the mutation codes?

A

cDNA

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13
Q

give an example of deletion mutation?

A

cystic fibrosis

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14
Q

what mutation causes cystic fibrosis?

A

deletion mutation that deletes the phenylalanine (F) residue at position 508 in the protein.
ΔUUU codon CFTR gene on chr. 7.
ΔF508

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15
Q

what does deletion mutation cause in the intron?

A

induces aberrant splicing of the DMD gene causing Duchene Muscular Dystrophy

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16
Q

what effect does Autosomal Dominant Inheritance have on characteristics?

A

Characteristic is manifested in the heterozygote of both sexes

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17
Q

is Autosomal Dominant Inheritance linked to a sex chromosome?

A

no

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18
Q

what is the chance of passing Autosomal Dominant Inheritance to offspring?

A

1 in 2

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19
Q

are homozygotes for Autosomal Dominant Inheritance rare?

A

are very rare and often have a more severe phenotype or show characteristic much earlier

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20
Q

what effect does homozygous for BMPR2 have?

A

embryonically lethal

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21
Q

what is Autosomal Dominant Inheritance?

A

both sexes affected and equally

likely to pass on the affected characteristic, e.g. PAH

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22
Q

what effect does Autosomal Recessive Inheritance have on characteristics?

A

Characteristic is not manifested in the heterozygote of both sexes

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23
Q

is Autosomal Recessive Inheritance linked to a sex chromosome?

A

no

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24
Q

is Autosomal Recessive Inheritance double defect?

A

yes

25
Q

who does Autosomal Recessive Inheritance effect?

A

Affected individuals are born to unaffected parents

26
Q

what is the chance of an affected parent passing on Autosomal Recessive Inheritance?

A

¼ as each parent has one WT allele and one mutant (affected) allele

27
Q

what is Compound heterozygote?

A

refers to an affected individual with 2 different mutant alleles

28
Q

what is true homozygotes?

A

Where an affected individual is from a consanguinous relationship then the 2 different mutant alleles will be the same

29
Q

what are most classical genetic diseases?

A

autosomal recessive

30
Q

what is Autosomal Recessive Inheritance?

A

both sexes affected.

The parents of the affected children in IV are both carriers

31
Q

what do mutations responsible for recessive traits usually lead to?

A

Lack of gene expression
Lack of protein production
Production of a protein with reduced or absent function

32
Q

what effect does X-linked Dominant Inheritance have on characteristics?

A

Characteristic is manifested in the heterozygote of both sexes

33
Q

who is affected by X-linked Dominant Inheritance?

A

One parent is affected

There are significantly more affected females than males

34
Q

what do females affected by X-linked Dominant Inheritance show?

A

typically show milder characteristics (and more variable expression) than males

35
Q

what is the chance of a child being affected is this mother is affected by X-linked Dominant Inheritance?

A

1 in 2 chance

36
Q

what is the effect of a male child having a father affected by X-linked Dominant Inheritance?

A

child will be unaffected (male child receives the Y chromosome from their father) but every daughter will be affected but show milder characteristics.

37
Q

what effect does X-linked Recessive Inheritance have on characteristics?

A

Characteristic is not manifested in the heterozygote of both sexes

38
Q

who are mostly affect by X-linked Recessive Inheritance?

A

males
Affected males are born to unaffected parents
No male- to male inheritance

39
Q

what are the chances of sons and daughters being affected in X-linked Recessive Inheritance?

A

Sons -1 in 2 risk of being affected daughters -not affected they have a 1 in 2 risk of being a carrier.

40
Q

what is manifesting heterozygotes?

A

Females through non-random mosaicism (X-chromosome inactivation) can show affects

41
Q

can one gene cause different diseases?

A

yes more diseases attributed to mutations in single genes than genes mutated

42
Q

what is Genetic Heterogeneity?

A

Different mutation in the same gene can lead to different diseases

43
Q

what is Achondroplasia caused by?

A

by constitutively active –’Gain of function’ mutation

44
Q

what mutation causes Achondroplasia?

A

Mutation in the fibroblast growth factor type 3 receptor leads to constitutive activity un-regulated by the receptor (FGFR3) function

45
Q

what does FGFR3 do?

A

promotes differentiation of cartilage into bone

46
Q

what does Gain-of-function mutation activate?

A

activates the receptor causing premature conversion of the growth plate into bone

47
Q

can multiple genes cause one disease?

A

yes

48
Q

give an example of when multiple genes cause one disease?

A

Xeroderma pigmentosum (XP)

49
Q

how does Xeroderma pigmentosum (XP) occur?

A

Mutations in 8 different genes that all function in DNA-damage repair lead to XP (8 variants) / DNA replication

50
Q

what other factors influence the phenotype of single gene disorders?

A

penetrance
expressivity
phenocopy
environmental effects

51
Q

what is penetrance?

A

The frequency with which a person manifests the gene that they possess

52
Q

do all dominant mutations display penetrance?

A

Not all display 100% penetrance

53
Q

what is penetrance determined by?

A

genetic and environmental factors

54
Q

what is expressivity?

A

Variation in the severity of the symptoms caused by a mutation

55
Q

give an example of expressivity?

A

in sickle cell anaemia (which is always caused by the same mutation) symptoms range from very severe to extremely mild

56
Q

what is phenocopy?

A

An environmental modification that mimics a genetic disease

57
Q

give an example of phenocopy?

A

confusing genetic deafness with deafness caused by Rubella during pregnancy

58
Q

give examples of environmental effects that influence the phenotype of single gene disorders?

A

phenylketonuria, a disease that once diagnosed is treatable via provision of a low phenylalanine diet
hypoxia many induce pulmonary arterial hypertension (PAH)

59
Q

what types of tests are carried out?

A 
Newborn screening
Diagnostic testing
Carrier testing (test for parents if carry one copy of mutation, that in 2 copies causes a disorder)
Prenatal testing
Preimplantation genetic diagnosis
Predictive and presymptomatic testing

IMS (52 decks)

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