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03 Biochemistry > 19 Single Gene Disorders > Flashcards

19 Single Gene Disorders Flashcards

1
Q

What is pseudoautosomal regions

A

some homologous regions on X and Y chromosome

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2
Q

What is Polymorphism and make an example and where is this gene located

A

When a specific site on a chromosome has multiple alleles in the population
β-globin gene, chromosome 11p15

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3
Q

Name different type of mutations

A 
Missense mutations
Nonsense mutations
Insertion
Deletion
In-frame
Frameshift
loss-of-function
Gain-of-function
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4
Q

Example for missense mutation

what is substituted in it

A

sickle cell disease is caused by a missense mutation

substitution of valine for glutamic acid in the β-globin

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5
Q

Examples for loss-of-function mutations

A

Phenylketunuria
Tay-Sachs
Sickle cell disease
CF

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6
Q

Examples for Gain-of-function mutations

A

Oncogens

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7
Q

What is a proband

A

The first affected individual to be identified in the family in a pedigree

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8
Q

Name some Autosomal Dominant inheritance

A 
Familial hypercholesterolemia (LDL receptor deficiency)
Huntington disease
Neurofibromatosis type 1
Marfan syndrome
Acute intermittent porphyria
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9
Q

what is the clue for AD inheritance in a pedigree

A

typically observed in multiple generations of a pedigree

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10
Q

Name some Autosomal Recessive inheritance

A

Sickle cell anemia
Cystic fibrosis
Phenylketonuria
Tay-Sachs disease (hexosaminidase A deficiency)

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11
Q

what is the clue for AR inheritance in a pedigree

A

Autosomal recessive diseases are typically seen in only one generation of a pedigree
Consanguinity

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12
Q

Name some X-linked Recessive Inheritance

A

Duchenne muscular dystrophy
Lesch-Nyhan syndrome (hypoxanthine-guanine phosphoribosyltransferase [HGPRT] deficiency)
Glucose-6-phosphate dehydrogenase deficiency
Hemophilia A and B
Red-Green colour blindness
Menke’s Disease
Ornithine transcarbamoylase (OTC) deficiency
SCID (IL-receptor γ-chain deficiency)

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13
Q

What does hemizygous mean

A

males are said to be hemizygous for the X chromosome in X-linked Recessive Inheritance

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14
Q

what is the clue for X-linked recessive inheritance in a pedigree

A

much more commonly in males
Skipped generations are commonly seen
Male-to-male transmission is not seen

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15
Q

What is the Mechanisms of X inactivation

A

Occurs in the blastocyst (-100 cells)
Gene called XIST is responsible
Methylation of gene regions
produce heterochromatin and Barr body

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16
Q

What are Characteristics of x-inactivation

A

Random: 50% of active is paternal, 50% is maternal
Fixed: once occurs stays throughout life
Incomplete: tips of both the long and short arms, that are not inactivated
One remain from any number of X

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17
Q

how much protein does sexual chromosomes code

why does x inactivated

A

Y carries only about 30 protein-coding genes
X carries hundreds of protein-coding genes
equalize the amount of protein encoded by X

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18
Q

Name some X-linked Dominant Inheritance

A

Hypophosphatemic Rickets

Fragile X Syndrome

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19
Q

Symptoms and penetrance of Fragile X Syndrome

A 
Males: 100% penetrance
• Mental retardation
• Large ears
• Prominent jaw
• Macro-orchidism (usually postpubertal)
Females: 60% penetrance
• Mental retardation
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20
Q

What is penetrance

A

Percentage of individuals who are known to have the disease-causing genotype who display the disease phenotype

21
Q

Name some Mitochondrial Inheritance

A

Leber hereditary optic neuropathy

MELAS: mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes

Myoclonic epilepsy with ragged red muscle fibers

22
Q

What is Heteroplasmy

A

Sometimes a specific mutation is seen in only some of the mitochondria

Variations in heteroplasmy can result in substantial variation in the severity of expression

23
Q

What is Variable Expression

A

Disease severity varies from patient to patient but they all manifest the symptoms

24
Q

What are some examples of Variable Expression

A

Hemochromatosis
Neurofibromatosis Type 1
xeroderma pigmentosum
hemophilia

25
Q

what factors are affecting Variable Expression and what are their examples

A

Environmental Influences: bleeding in Hemochromatosis or UV exposure in xeroderma pigmentosum
Allelic Heterogeneity: missense vs nonsense in hemophilia - variety between families
Heteroplasmy
Modifier Loci

26
Q

inheritance, penetrance, symptoms, gene of hemochromatosis

A

autosomal recessive, penetrance of 15%
arthritis, significant hepatomegaly, diabetes, and “bronze” skin, cirrhosis
mutation C282y
incomplete penetrance and also an example of variable expression

27
Q

What is Incomplete penetrance

A

no presentation or phenotype vs decreased symptoms in variable expression

28
Q

What are some examples of Incomplete penetrance

A

Retinoblastoma
Inherited Breast Cancer
hemochromatosis

29
Q

Explain pattern of Inheritance, penetrance and mechanism of gene expression in Rb

A

Autosomal dominant loss-of-function mutation
Both Rb gene must be mutated: “loss of heterozygosity” will make the disease appear: Two hit theory
Penetrance of 90%

30
Q

Explain pattern of Inheritance, penetrance in Inherited Breast Cancer

A

BRCA I & BRCA II
AD follow two hit theory
70% penetrance

31
Q

What is Pleiotropy

A

single disease-causing mutation affects multiple organ systems

32
Q

What are some examples of Pleiotropy

A

Marfan syndrome

Cystic fibrosis

33
Q

What is etiology and symptoms of Marfan

A 
A mutation in the gene that encodes fibrillin
skeletal abnormalities (thin, elongated limbs, pectus excavatum, pectus carinatum), hypermobile joints
ocular abnormalities (frequent myopia and detached lens)
cardiovascular disease (mitral valve prolapse and aortic aneurysm)
34
Q

What is Locus Heterogeneity

A

same disease phenotype can be caused by mutations in different loci

35
Q

What are some examples of Locus Heterogeneity

A

Osteogenesis Imperfecta Type 2

36
Q

What is Etiology, chromosome defect and pattern of inheritance in Osteogenesis Imperfecta Type 2

A

AD, Defect in type 1 collagen
100% of individuals are the result of a new mutation in the family
Two memberson chromosome 17, third is on chromosome 7

37
Q

What are some examples of Delayed Age of onset

A

Acute intermittent porphyria (peri- or postpubertal), Huntington disease
Hemochromatosis
Familial breast cancer

38
Q

What is pattern of inheritance, symptoms, chromosome defect, kind of gene(also in normal people) involvement in Huntington

A

Autosomal dominant
progressive dementia, loss of motor control, and affective disorder, Death 10-15 years after onset
Gain-of-function mutation on chromosome 4
Normal huntingin genes have fewer than 27 CAG repeats in the 5’ coding region
premutations of 27-35 repeats are seen: can be inherited by generally by males
more than 39 repeats develop symptoms

39
Q

What is Anticipation

A

recent generation of a pedigree develop a disease at an earlier age or with greater severity

40
Q

What is the etiology of Anticipation

A

gradual expansion of trinucleotide repeat polymorphisms within or near a coding gen

41
Q

What are some examples of Anticipation

A

Huntington disease
Fragile X syndrome
Myotonic dystrophy
Friedreich ataxia

42
Q

What is pattern of inheritance, symptoms, kind of gene involvement in Fragile X syndrome

A

X dominant
Mental retardation, Large ears and jaw
Post-pubertal macro-orchidism (males)
Attention deficit disorder (in females)

CGG 5’UTR

43
Q

What is pattern of inheritance, symptoms, kind of gene involvement in Myotonic dystrophy

A

Autosomal dominant
Muscle loss, Cardiac arrhythmia, Testicular atrophy
Frontal baldness, Cataracts

CTG 3’UTR

44
Q

What is pattern of inheritance, symptoms, name and kind of gene involvement in Friedreich ataxia

A

Autosomal recessive
Early onset progressive gait and limb ataxia, Areflexia in all 4 limbs, Hypertrophic cardiomyopathy
Axonal sensory neuropathy, Kyphoscoliosis

GAA Intron 1 in frataxin gene
Life expectancy about 40

45
Q

What is Imprinting

A

small number of genes are transcriptionally active only when transmitted by one of the two sexes
Occurs during gametogenesis
During gametogenesis in the offspring, is erased and re-established according to the sex of the individual
Involves methylation and other mechanisms

46
Q

What are some examples of Imprinting

A

Prader-Willi Syndrome

Angelman Syndrome

47
Q

What are Symptoms, chromosome and gene involved in Prader-Willi Syndrome

A

Neonatal hypotonia, Poor feeding in neonatal period, Behavior problems (temper tantrums), Moderate mental and developmental retardation, Hypogonadism, underdeveloped genitalia
Hyperphagia (overeating) and obesity by ages 2-4 years, Small hands and feet

Deletion from paternal 15q11-13 that include SNRPN , Very low recurrence risk

48
Q

What are Symptoms, chromosome and gene involved in Angelman Syndrome

A

Severe mental retardation, Seizures, Ataxia, Puppet-like posture of limbs, Happy disposition: Happy Puppet syndrome

Deletion from maternal 15q11-13 include a ubiquitin pathway known as UBE3A, Very low recurrence risk

03 Biochemistry (5 decks)

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