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IMMS > Multifactorial Inheritance > Flashcards

Multifactorial Inheritance Flashcards

1
Q

Genetics cause…

A

Down syndrome
Cystic fibrosis
Huntington disease
Haemophilia

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2
Q

Environmental (malnutrition,trauma)

A

Poor diet
Infection
Drugs
Accidents

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3
Q

In between genetic and environmental (Multifactorial)

A

Spina bifida
Cleft lip/palate
Diabetes
Schizophrenia
Hypertension

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4
Q

Definition of Multifactorial

A

Diseases that are due to a combination of genetic and environmental factors
Most common diseases are Multifactorial

If the condition is more common in one particular sex, the relatives of an affected individual of the less frequently affected sex will be a higher risk than relatives of an affected individual or the more frequently affected sex i.e if a boy has the condition then female relatives are more at risk and vice versa.

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5
Q

How do you identify that a condition has a
genetic component?

A

By clinical observation
Family studies
Twin studies
Adoption studies

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6
Q

Family studies- is when the incidence of a disease is compared amongst the relatives of the affected individual with the general population

A

In Multifactorial condition:

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7
Q

The risk of the condition in relatives of an affected individual is dramatically higher than in the general population

A

the risk varies directly with the degree of genetic relationship

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8
Q

the risk varies with the severity of the proband’s illness

A

Proband: person serving as the starting point for the genetic study of a family

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9
Q

the risk varies with the number of relatives affected

A
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10
Q

Monozygotic twins

A

Genetically identical

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11
Q

Dizygotic twins

A

Genetically non identical twins

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12
Q

Concordance

A

The inheritance by two related individuals of the same genetic characteristics

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13
Q

concordance rate

A

the % of twin pairs studied that both have the condition.

The concordance rates give a rough figure for the hereditability of a multifactorial disorder

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14
Q

If a condition has a genetic component you would expect the concordance rate to be higher in monozygotic twins than in dizygotic twins

A

The high risk for MZ twins is found even when they are reared apart

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15
Q

Adoption studies

A

adopted children of a parent with a multifactorial condition have a high risk of developing the disease

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16
Q

Can look at adopted individuals with a condition and look at the rates of that condition in the biological and adoptive families

A

high in the biological families only

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17
Q

Hereditability

A

The proportion of the aetiology (causes) that can be ascribed to genetic factors as opposed to environmental factors

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18
Q

Heritability is expressed as…

A

as a proportion of 1 or as a percentage e.g.in schizophrenia hereditability is about 0.85 or 85%

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19
Q

Can calculate heritability from…

A

the concordance rate in monozygotic twins

20
Q

Characteristics of Multifactorial
Inheritance

A

• The incidence of the condition is greatest amongst relatives of the most severely affected patients
• The risk is greatest for the first degree relatives and decreases rapidly in more distant relatives
• If there is more than one affected close relative then the risks for other relatives are increased

21
Q

Characteristics of Multifactorial Inheritance

A

If the condition is more common in one particular sex, then relatives of an affected individual of the less frequently affected sex will be at higher risk than relatives of an affected individual of the more frequently affected sex.

22
Q

The Liability / Threshold Model

A

Look on GoodNotes ppt (slide 12)

23
Q

The Liability / Threshold Model

A

The factors that influence the development of a multifactorial disorder, genetic and environmental can be considered as a single entity known as liability

24
Q

Curve:

A

the liabilities of all individuals form a continuous variable which has a normal distribution

the curve for relatives is shifted to the right compared to the general population

the closer the relationship the greater the shift to the right

25
Q

a threshold exists above which the abnormal phenotype is expressed

A

in the general population the proportion beyond the threshold is the population incidence and among relatives is the familial incidence

26
Q

GWAS – Genome wide association studies

A

Utilises the fact that a gene can have several variants –alleles

27
Q

Pathogenic

A

Some variations in a gene cause that gene to be inactivated or behave abnormally

28
Q

Polymorphisms

A

frequent hereditary variations at a locus

Doesn’t cause problems (thats mutations)

Polymorphisms can be you more/less efficient or make you more/ less susceptible to disease.

When Most genetic variation still results in a functioning gene

29
Q

Different types of polymorphisms

A

SNPs (single nucleotide polymorphisms)
Differing lengths of a CA repeat.

30
Q

GWAS (example of prostate cancer in ppt slide 18)

A

compare the frequency of markers in a sample of patients and a sample of healthy controls.

Can use candidate genes or nowadays try to aim for complete coverage of the genome

Look for markers e.g. a SNP that is seen more frequently in the disease population

Sequence that area to try to identify the gene and the particular allele that is associated with the increased likelihood of developing the condition

31
Q

Neural Tube Defects (image on slide)

A

Defective closure of the developing neural tube during the first month of embryonic life

32
Q

Environmental factors

A

poor socioeconomic status
multiparity
valproate.

33
Q

Recurrence risks are about 4-5 % without treatment, highest in people of Celtic origin.

In Ireland about 10% of cases can be attributed to mutations in the methylenetetrahydrofolate (MTHFR) gene which leads to decreased plasma folate levels.

A

Periconceptual folate supplementation reduces recurrence risk to about 1%

34
Q

Environmental Agents acting on embryogenesis (images on slide)

A

Drugs and Chemicals e.g. thalidomide,
anticonvulsants, alcohol

Maternal Infections e.g. rubella, CMV

Physical Agents e.g. radiation

Maternal Illness e.g. diabetes, phenylketonuria

35
Q

Post-natal Environmental Factors

A

Type 2 diabetes- Obesity

Breast cancer- Hormonal factors: The pill, HRT, parity, breast feeding, obesity

Lung cancer-Smoking

Schizophrenia– Recreational drugs

36
Q

Using DNA:

A

What your DNA says about you

Carrier status- Find out if your children are at risk for inherited conditions, so you
can plan for the health of your family.

Health risks

Drug response- how your body will respond to drugs

37
Q

Autosomal

A

Chromosomes 1-22, all chromosomes except the sex chromosomes (XY)

38
Q

Locus

A

The position of a gene/DNA on the genetic map.

39
Q

Genotype

A

genetic constitution of an individual

40
Q

Phenotype

A

Appearance of an individual which results from the interaction of the environment and the genotype

41
Q

Variable expression

A

Variation in clinical features (type and severity) of a genetic disorder between individuals with the same gene alteration

42
Q

Sex limitation

A

Expression of a particular characteristic limited to one of the sexes

43
Q

Late-onset

A

Condition not manifested at birth (where it does this is called congenital).

Classically adult-onset e.g Huntington’s

44
Q

Barrbody

A

inactive X chromosome since packaged in heterochromatin (cannot be transcripted)

45
Q

Khudson’s 2-hit hypothesis

A

Gene mutations may either be inherited or acquired during a persons life

• Sporadic cancers = 2 acquired mutations

• Hereditary cancers = 1 inherited mutation + 1 acquired mutation

46
Q

Ideogram

A

diagrammatic form of chromosome bands, bands are numbered according to distance to centromere

IMMS (29 decks)

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