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Biochemistry- First Aid > Biochemistry First Aid- Genetics (pg 84-91) > Flashcards

Biochemistry First Aid- Genetics (pg 84-91) Flashcards

pgs 84-91 in First Aid 2014

1
Q

define codominance

A

when both alleles contribute to the phenotype

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2
Q

list some common examples of codominance

A

AB blood groups, alpha1-antitrypsin deficiency

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3
Q

define variable expressivity

A

phenotype varies among individuals with the same genotype

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4
Q

name a good neuro example of variable expressivity

A

NF1 (two patients with neurofibromatosis 1 will have varying disease severity)

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5
Q

define incomplete penetrance

A

not all individuals with the mutant genotype show the mutant phenotype

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6
Q

what is a commonly known cancer gene that exhibits incomplete penetrance

A

BRCA1 gene mutations do not always result in breast or ovarian cancer

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7
Q

what is pleiotropy

A

one gene results in multiple phenotypic effects

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8
Q

name a common condition that exhibits pleiotropy

A

PKU (phenylketonuria) manifests with light skin, intellectual disability, and musty body odor

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9
Q

what is anticipation

A

increased severity or earlier onset of disease in succeeding generations

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10
Q

what kind of genetic conditions show anticipation

A

trinucleotide repeat diseases (i.e. Huntington’s, several spinocerebellar ataxias, Fragile X syndrome, Freidrich’s ataxia, juvenile myoclonic epilepsy, myotonic dystrophy)

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11
Q

explain the concept of loss of heterozygosity

A

if a patient develops a mutation in a tumor suppressor gene the other allele must be either mutated or deleted before cancer can develop (not true of oncogenes)

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12
Q

what is a dominant negative mutation

A

a heterozygote produces a nonfunctional altered protein that impairs function of the normal gene product

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13
Q

describe a key example of dominant negative mutation

A

mutation of a transcription factor in its allosteric site. The non-functioning protein can still bind DNA, preventing wild-type transcription factor from binding

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14
Q

what is linkage disequilibrium and what kind of sample is used to measure it

A

it is the tendency for certain alleles at 2 linked loci to occur together more often than expected by chance. It is measured in a population, not in a family, and it often varies in different populations.

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15
Q

what is mosaicism and how does it come about

A

the presence of genetically distinct cell lines in the same individual. It arises from mitotic errors after fertilization.

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16
Q

name and explain the two types of mosaicism

A

somatic (mutation propagates in different organs)

gonadal (mutation propagates through egg or sperm cells)

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17
Q

name a commonly-known mosaic condition

A

McCune-Albright syndrome (lethal is somatic, but survivable if mosaic)

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18
Q

what is locus heterogeneity

A

mutations at different loci can produce a similar phenotype

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19
Q

what kind of genetic heterogeneity does beta-thalassemia exhibit

A

allelic heterogeneity

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20
Q

what kind of genetic heterogeneity does albinism exhibit

A

locus heterogeneity

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21
Q

define allelic heterogeneity

A

different mutations at the same locus produce the same phenotype

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22
Q

what is heteroplasmy

A

presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrial inherited disease

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23
Q

what is uniparental disomy

A

the offspring receives two copies of a chromosome from one parent and none from the other

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24
Q

what are the two ways uniparental disomy can occur

A

heterodisomy: (heterozygous) indicates a meiosis I error
isodisomy: (homozygous) indicates a meiosis II error or postzygomatic duplication of one of the chromosomes with loss of the other

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25
Q

in what kind of pedigree can you be fairly certain that a child has been affected by uniparental disomy

A

a child affected by a recessive disorder for which only one parent is a carrier (and the other is unaffected)

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26
Q

name four assumptions required for Hardy-Weinberg population genetics

A 
no mutation at the locus of interest
no net migration
random mating (no sexual selection)
no natural selection
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27
Q

what are the two Hardy-Weinberg equations

A

p^2 + 2pq + q^2= 1

p + q = 1

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28
Q

what is imprinting

A

at some loci only one allele is active while the other is inactivated via methylation (imprinted). With one allele inactivated, deletion/ mutation of the other allele leads to disease.

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29
Q

name two conditions that are commonly known to result from imprinting

A

Prader-Willi syndrome and Angelman syndrome

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30
Q

what is the clinical manifestation of Prader-Willi syndrome

A

hyperphagia, obesity, intellectual disability, hypogonadism, hypotonia

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31
Q

what kind of imprinting does Prader-Willi result from

A

materal imprinting (maternal gene is normally silent/imprinted and paternal gene gets mutated/deleted)

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32
Q

25% of Prader-Willi cases are due to this genetic phenomenon rather than imprinting

A

maternal uniparental disomy

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33
Q

what is the clinical manifestation of Angelman syndrome

A

inappropriate laughter, seizures, ataxia, severe intellectual disability

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34
Q

what kind of imprinting does Angelman syndrome result from

A

paternal imprinting (paternal gene is normally silent/imprinted and maternal gene is mutated/ deleted)

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35
Q

5% of cases of Angelman syndrome result from this genetic phenomenon rather than from imprinting

A

paternal uniparental disomy

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36
Q

name 5 modes of inheritance

A

autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, mitochondrial

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37
Q

what is the mode of inheritance of hypophosphatemic rickets

A

X-linked dominant

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38
Q

what is the inheritance pattern of mitochondrial myopathies and how do they present

A

mitochondrial inheritance;
present with myopathy, lactic acidosis, CNS disease, all as a result of failure in oxidative phosphorylation
(on biopsy: ragged red fibers)

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39
Q

name as many autosomal dominant diseases as you can

A

ADPKD, familial hypercholesterolemia, familial adenomatous polyposis, hereditary hemorrhagic telangiectasia, hereditary spherocytosis, Huntington’s, Marfan’s, MEN, NF1, NF2, tuberous sclerosis, VHL

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40
Q

85% of cases of ADPKD are due to what mutation and on what chromosome
15% of cases of ADPKD are due to what mutation and on what chromosome

A

85% of cases from gene PKD1 on chromosome 16

15% of cases from gene PKD2 on chromosome 4

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41
Q

what is the clinical manifestation of familial adenomatous polyposis

A

adenomatous polyps in the colon that develop post-puberty and can progress to colon cancer if not resected

42
Q

what gene and on what chromosome is the mutation for familial adenomatous polyposis

A

APC “adenomatous polyposis of colon”

on chromosome 5

43
Q

what is the defect in familial hypercholesterolemia

A

defective or absent LDL receptor leading to elevated LDL and eventual severe atherosclerotic disease early in life (xanthomas such as Achilles tendon xanthoma)

44
Q

what is the clinical manifestation of hereditary hemorrhagic telangiectasia (aka Osler-Weber-Rendu syndrome)

A

telengiectasias, recurrent epistaxis, skin discolorations, AVMs, GI bleeding, hematuria

45
Q

what is the defect in hereditary spherocytosis

A

defective ankyrin or spectrin –>spheroid erythrocytes and hemolytic anemia

46
Q

what is the mutation in Huntington’s disease and on what chromosome

A

CAG trinucleotide repeats in the huntingtin gene on chromosome 4

47
Q

what is the defective gene product in Marfan syndrome and what organs are affected as a result

A

fibrillin-1 gene –> defective connective tissue –> defects in skeleton (long extremities, pectus excavatum, hypermobile joints, arachnodactyly), heart/vessels (medial calcific necrosis of aorta, floppy mitral valve) and eyes (subluxation of lens)

48
Q

what gene are MEN2A and MEN2B associated with

A

ret

49
Q

on what chromosome is the NF1 gene

A

chromosome 17

50
Q

what are the most common findings for neurofibromatosis type 1 on physical exam

A

cafe au-lait spots, neurofibromas, Lisch nodules

51
Q

how much penetrance does neurofibromatosis type 1 show

A

100% penetrance

52
Q

what gene and chromosome is mutated in neurofibromatosis type 2

A

NF2 gene on chromosome 22

53
Q

what are the characteristic findings of neurofibromatosis type 2

A

bilateral acoustic neuromas, meningiomas, ependymomas, juvenile cataracts

54
Q

what kind of tissue pathology characterizes tuberous sclerosis

A

hammartomas

55
Q

how much penetrance does tuberous sclerosis show

A

incomplete penetrance

56
Q

what gene and what chromosome is mutate in von Hippel Lindau

A

VHL gene on chromosome 3

57
Q

name as many autosomal recessive disorders as you can

A

albinism, ARPKD, cystic fibrosis, glycogen storage diseases, hemochromatosis, Kartagener’s syndrome, mucopolysaccharidoses (except Hunter syndrome), phenylketonuria, sickle cell anemia, sphingolipidoses (except Fabry disease), thalassemias, Wilson disease

58
Q

in what gene and on what chromosme is the mutation that causes cystic fibrosis

A

CFTR gene on chromosome 7

59
Q

what is the gene product that is defective in cystic fibrosis

A

ATP-gates Cl- channel that secretes Cl into lungs and GI tract and reabsorbs Cl in sweat glands
–> Cl retained in cells –> Na and H2O retained in cells –> thick secretions

60
Q

how is cystic fibrosis diagnosed

A

> 60mEq/L of Na in sweat

61
Q

what are common complications of cystic fibrosis

A

Pseudomonas infection, chronic bronchitis and bronchiectasis, pancreatic insufficiency, malabsorption, steatorrhea, nasal polyps, infertility in males, fat soluble vitamin deficiencies

62
Q

name to pharmacologic treatments for cystic fibrosis

A 
N-acetylcysteine (breaks disulfide bonds in mucus glycoproteins)
dornase alpha (clears leukocytic debris)
63
Q

name as many X-linked recessive disorders as possible

A

Bruton agammaglobulinemia, Wiskott-Aldrich syndrome, Fabry disease, G6PD deficiency, ocular albinism, Lesch-Nyhan syndrome, Duchenne and Becker muscular dystrophy, Hunter syndrome, Hemophilia A and B, Ornithine transcarbamoylase deficiency

64
Q

Duchenne muscular dystrophy is caused by what kind of mutation and to what protein? what inheritance?

A

frameshift mutation to dystrophin protein (anchors muscle fibers by connecting actin to transmembrane proteins called alpha and beta dystroglycan)
X-linked recessive

65
Q

what are some clinical signs and symptoms you would see in a Duchenne Muscular Dystrophy patient

A

pseudohypertrophy of calf muscles (fibrous fatty replacement of muscle), Gower maneuver (using UE to help stand up), muscle weakness that begins in the pelvic girdle and ascends

66
Q

when is the typical onset of Duchenne Muscular Dystrophy

A

before 5 years old

67
Q

what is the most common cause of death in Duchenne Muscular Dystrophy

A

dilated cardiomyopathy

68
Q

what enzyme levels would be increased in Duchenne Muscular Dystrophy

A

creatinine phosphokinase (CPK) and aldolase

69
Q

how is diagnosis of Duchenne Muscular Dystrophy confirmed

A

Western blot and muscle biopsy

70
Q

what is unique about the dystrophin gene (DMD)

A

has the longest coding region of any human gene

71
Q

what’s the difference between the mutation in Duchenne vs. Becker Muscular Dystrophy

A 
Duchenne= X-linked recessive frameshift
Becker= X-linked recessive in frame deletion
72
Q

what’s the difference between Duchenne vs. Becker Muscular Dystrophy in terms of onset and severity

A

Duchenne’s has earlier onset (s is less severe and onset occurs in adolescence or early adulthood

73
Q

what causes Myotonic type I Muscular Dystrophy

A

CTG trinucleotide repeat expansion in DMPK gene

74
Q

what protein is affected in Myotonic type I Muscular Dystrophy

A

abnormal expression of myotonin protein kinase

75
Q

what are the clinical manifestations of Myotonic type I Muscular Dystrophy

A

myotonia, muscle wasting, frontal balding, cataracts, testicular atrophy, arrhythmia

76
Q

what gene is affected in Fragile X syndrome

A

FMR1 (fragile X mental retardation) gene, which is responsible for normal neural development

77
Q

what is the heredity of Fragile X syndrome

A

X-linked (due to X inactivation in females no distinction is made between dominant vs. recessive)

78
Q

what are the clinical manifestations of Fragile X syndrome

A

intellectual disability (2nd most common genetic cause after Down’s), macroochidism (opposite of Myotonic type 1 MD), long face with large jaw and forehead, large everted ears, autism, mitral valve prolapse, arched palate

79
Q

what is the trinucleotide repeat in Fragile X syndrome

A

CGG

80
Q

name 4 major trinucleotide repeat expansion diseases and what the associated codons are

A

Huntington’s (CAG), Friedrich’s ataxia (GAA), Fragile X syndrome (CGG), Myotonic type 1 MD (CTG)

81
Q

what are the clinical manifestations of Down’s syndrome (include disease risks associated with Down’s)

A

intellectual disability, flat facies, prominent epicanthal folds, single palmar crease, space between toe 1 and 2, duodenal atresia, Hirschsprung’s, ASD, Brushfield spots (light spots around periphery of iris);
increased risk of ALL, AML, Alzheimer’s

82
Q

95% of Down syndrome cases are due to what meiotic abnormality

A

meiotic nondisjunction of homologous chromosomes

83
Q

4% of Down syndrome cases are due to what meiotic abnormality

A

Robertsonian translocation

84
Q

1% of Down syndrome cases are due to what defect/ abnormal process

A

mosaicism (no maternal association); post-fertilization mitotic error

85
Q

what would be seen in first trimester and in second trimester that would suggest Down syndrome

A

1st trimester: increased nuchal translucency, hypoplastic nasal bone, low serum PAPP-A, high free beta-hCG
2nd trimester: low alpha-fetoprotein, high beta-hCG, low estriol, high inhibin A

86
Q

what genetic defect causes Edward syndrome

A

trisomy 18

87
Q

what are the clinical manifestations of Edward syndrome

A

rocker bottom feet, severe intellectual disability, micrognathia (small jaw), low-set ears, clenched hands, prominent occiput (occipital bone), congenital heart disease, death within 1st year of life

88
Q

what prenatal labs values are suggestive of Edward syndrome

A

decreased beta-hCG and PAPP-A (pregnancy associated plasma protein A) in 1st trimester
quad screen shows: decreased alpha-fetoprotein, beta-hCG, estriol, and low or normal inhibin A

89
Q

what does a quad screen test for and when is it done

A

quad screen is a blood screen that tests for alpha-fetoprotein, beta-hCG, estriol and inhibin A
done at 16-18 weeks (2nd trimester)

90
Q

what genetic abnormality causes Patau syndrome

A

trisomy 13

91
Q

what are the clinical manifestations of Patau syndrome

A

severe intellectual disability, rocker bottom feet, microphthalmia, microcephaly, cleft lip/palate, holoprosencephaly, polydactyly, congenital heart disease, death within 1 year of birth

92
Q

what abnormalities would be seen on first trimester screen

A

decreased free beta-hCG, decreased PAPP-A, increased nuchal translucency

93
Q

define Robertsonian translocation

A

a common type of translocation that occurs when the long arms of two acrocentric chromosomes fuse at their centromeres, losing the 2 short arms

94
Q

what chromosomes typically experience Robertsonian translocation

A

13, 14, 15, 21, 22

95
Q

which diseases can be caused by unbalanced Robertsonian translocation

A

Down syndrome, Patau syndrome

96
Q

what causes cri-du-chat syndrome

A

microdeletion of short (p) arm of chromosome 5

97
Q

what are the clinical manifestations of cri-du-chat

A

microcephaly, moderate to severe intellectual disability, high-pitched crying, epicanthal folds, cardiac abnormalities (VSD)

98
Q

what causes Williams syndrome and what specific important gene is deleted

A

congenital microdeletion of long (q) arm of chromosome 7;

elastin gene is deleted

99
Q

what are the clinical manifestations of Williams syndrome

A

elfin facies, intellectual disability, hypercalcemia (decreased sensitivity to vit D), well-developed verbal skills, extreme friendliness with strangers, cardiovascular problems

100
Q

what two syndromes are caused by deletion of 22q11 and what are their symptoms

A

Di George (thymic aplasia=> T cell def., hypocalcemia, cardiac defects) and Velocardiofacial (cleft palate, abnormal facies, cardiac defects) syndromes

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