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Biochemistry > Multifactorial Inheritance > Flashcards

Multifactorial Inheritance Flashcards

1
Q

Multifactorial inheritance

A

Polygenic- many genes contribute to a trait, true for most quantitative traits, may show a normal distribution

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2
Q

Threshold model

A

Some diseases are only present or absent, distribution in population is not that of single genes

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3
Q

Liability distribution

A

Individuals at one end of the curve are affected

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4
Q

Threshold of liability

A

Limit separates normal from affected, may differ by sex or other factor

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5
Q

Recurrence risk

A

Complex, unknown number of genes, degree to which each gene and allele contributes, genetic constitution of parents unknown, environmental influence varies, empirical risks are derived

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6
Q

Specific indications

A

Relative recurrence risks- higher if more than one affected family member, higher if proband is more severely affected, higher if proband is of less affected sex, decreases rapidly with more distant relationship, risk to siblings and offspring is sqrt of population risk

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7
Q

Locus heterogeneity

A

Mutations in different genes give similar phenotype, different families have different mutations, in any one family a single mutation in a single gene

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8
Q

Background effects on major genes

A

One gene accounts for significant variation, influenced by environment or modifier genes, overall effect is continuous distribution

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9
Q

Twin studies

A

Compare monozygotic (100%) to dizygotic twins (50%), determine relative recurrence rate of trait

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10
Q

Concordant

A

Both twins are affected

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11
Q

Discordant

A

One twin affected, one is not

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12
Q

Concordance rate

A

For qualitative traits

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13
Q

Intraclass correlation

A

For quantitative traits

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14
Q

Measuring heritability

A

Heritability is the difference between monozygotic and dizygotic twin concordance rate, proportion of variance of a trait that is determined by genes, measured from 0 to 1

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15
Q

Adoption studies

A

Compare inheritance of trait in adopted vs. natural children, compare adopted children from affected parents vs. adopted children of unaffected parents

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16
Q

Finding genes

A

More complex than single-gene traits, may be multiple causes- specific genes, phenocopies, look for quantitative trait loci (QTLs)

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17
Q

Phenocopies

A

Have trait but not with genetic cause, possibly environmental

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18
Q

Finding quantitative trait loci (QTLs)

A

Population with affected and unaffected members, perform genome scan, genetic constitution at many loci scattered throughout the genome, compare alleles at each locus with trait, locate regions which correlate with trait

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19
Q

Affected sib-pair method

A

Two siblings affected with the same disorder, share ~50% of genes, must share genes causing effect, use pairs from many families, compare to each other and unaffected siblings, find regions in common

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20
Q

Common multifactorial disorders

A

Identifying major genes aids in risk estimates, health problems to consider- heart disease, hypertension, diabetes

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21
Q

Heart disease

A

Mainly coronary artery disease (CAD), narrowed by atherosclerosis, fatty deposits, impedes blood flow, can lead to myocardial infarction or stroke, risk factors- obesity, cigarettes, hypertension, high cholesterol

22
Q

Family history

A

Positive family history increases risk 2-7 fold, greater risk with more affected relatives, affected relative is female, early age of onset for affected relative

23
Q

Familial hypercholesterolemia (FH)

A

Quantitative trait with a major gene, autosomal dominant inheritance, doubles serum cholesterol, accelerates atherosclerosis, produces xanthomas (fatty deposits), higher risk of coronary artery disease and MI, homozygotes more severely affected

24
Q

LDL receptor

A

LDL in blood binds to LDLR, glycoprotein made in RER, pass through Golgi, LDL is endocytosed into cells with LDLR, receptor delivers LDL to lysosome, LDL breaks down, receptor recycles to surface

25
Q

LDLR mutations

A

Fall into 5 classes based on defect- I-V

26
Q

Class I LDLR mutation

A

No protein found

27
Q

Class II LDLR mutation

A

Cannot leave ER, degraded

28
Q

Class III LDLR mutation

A

Cannot bind LDL

29
Q

Class IV LDLR mutation

A

Do not migrate to coated pits (rare)

30
Q

Class V LDLR mutation

A

Cannot dissociate from LDL, not recycled to cell surface

31
Q

Possible therapies for FH

A

Decrease intake of cholesterol and fats, bile-acid binding resins (cholestyramine), statins block cholesterol synthesis

32
Q

Bile-acid binding resins

A

Limits recycling from intestine, liver increases synthesis of LDLR and cholesterol

33
Q

Statins for blocking cholesterol synthesis

A

HMG CoA reductase activity targeted, LDLR synthesis increased

34
Q

Hypertrophic cardiomyopathy

A

Half familial, autosomal dominant mutations in 10 genes for sarcomere- beta-myosin heavy chain (35%), myosin-binding protein C (20%), troponin T (15%)

35
Q

Dilated cardiomyopathy

A

1/3 familial, autosomal dominant, X-linked and mitochondrial mutations- actin, cardiac troponin T, desmin

36
Q

Long QT cardiomyopathy

A

Delayed repolarization due to affected potassium and sodium channels

37
Q

Factors in stroke

A

Mitochondrial disorder MELAS, mutations in NOTCH3 (also causes dementia), protein C and S mutations (normally inhibit clotting), factor V Leiden (increases clotting)

38
Q

Factors in hypertension

A

Present in a few single gene mutations as one symptom- Liddle syndrome, Gordon syndrome, rare disorders of corticosteroid production

39
Q

Liddle syndrome

A

Defective epithelial sodium channel (ENaC)

40
Q

Gordon syndrome

A

Increased renal salt reabsorption (WNK2 or WNK4 kinases)

41
Q

Type I diabetes

A

Early onset, immune destruction of pancreatic islet cells, lack of insulin

42
Q

Type II diabetes

A

Late onset, usually with obesity, peripheral insulin resistance

43
Q

MODY

A

Maturity onset diabetes of the young, intermediate onset, autosomal dominant pattern, no association with obesity

44
Q

Risks for type I diabetes

A

Siblings at increased risk, diabetic parent increases risk (higher for father), monozygotic twins are 30-50% concordant (not entirely genetic, autoimmune, specific viral infection)

45
Q

HLA association in type I diabetes

A

95% Caucasian type I, HLA DR3 or DR4, only 50% of generation population is DR3 or DR4, share with sibling, recurrence risk increased, no aspartate at position 57, 100x risk

46
Q

VNTR polymorphism

A

5’ to insulin gene, may affect insulin transcription, insulin region polymorphism could account for 10% of familial clustering

47
Q

Risk for type II diabetes

A

90% of diabetes cases, high concordance in monozygotic twins, 10-15% recurrence in first degree relatives, obesity and positive family history are risks, increases with too much food and too little exercise

48
Q

Genes in type II diabetes

A

Mutations in calpain-10, common mutation in PPAR-gamma transcription factor gene- involved in adipocyte differentiation, increases risk by 25%, found in 75% of people of European descent

49
Q

MODY genes

A

1-5% of cases, autosomal dominant, glucokinase mutations in 50% of cases

50
Q

Transcription factors responsible for pancreatic development or insulin regulation

A

Hepatocyte nuclear factor 1 alpha (HNF1alpha)
Hepatic nuclear factor 1 beta (HNF1beta)
Hepatocyte nuclear factor 4 alpha (HNF4alpha)
Insulin promoting factor 1 (IPF1)
Neurogenic differentiation 1 (NEUROD1)

51
Q

Risks for obesity

A

BMI >30, leptin deficiency- leptin deficient humans are morbidly obese, neuropeptide Y and MCR4- appetite control, mutations in 3-5% of severely obese

52
Q

Alzheimer disease

A

10% over 65, 40% over 85, risk doubles if first-degree relative affected, few autosomal dominant cases, Presenilin-1 or -2, part of cleavage of APP precursor, gain of function mutants, some cases with APP mutation, certain ApoE alleles increase risk

Biochemistry (18 decks)

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