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USMLE > Biochemistry - Genetics > Flashcards

Biochemistry - Genetics Flashcards

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USMLE® Step 1 flashcards
1
Q

Which traits are codominantly expressed ?

A

ABO blood type, alpha-1-antitrypsin deficiency

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2
Q

What is incomplete penetrance?

A

Possessing a mutant genotype doesn’t guarantee a mutant phenotype

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3
Q

What is pleiotropy?

A

1 gene mutation can have multiple phenotypic effects

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4
Q

What is genetic anticipation?

A

Increasing severity or earlier onset of disease in successive generations (TNR diseases)

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5
Q

Give an example of loss of heterozygosity

A

Somatic retinoblastoma, Lynch syndrome, Li-Fraumeni (inherit one bad, one good copy, one good copy must be lost for bad to show)

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6
Q

Linkage disequilibrium

A

Tendency of two genes close on a loci to occur together more or less often than by chance. Measured in population s

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7
Q

What is somatic mosaicism

A

Genetically distinct cell line in individual that arises from mitotic errors after fertilization and propagates through multiple tissues or organs

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8
Q

Gonadal mosaicism

A

Mutation only in egg or sperm cells (mutation may show in offspring but not parent)

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9
Q

What is McCune Albright syndrome?

A

Mutation of G-protein signaling pathway. Presents as unilateral cafe-au-lait spots, polyostic fibrous dysplasia, precocious puberty, multiple endocrine endocrine abnormalities

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10
Q

When is McCune Albright syndrome lethal?

A

When mutation occurs before fertilization

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11
Q

Which part of collagen synthesis is Vitamin C necessary?

A

Hydroxylation of specific proline and lysine residues

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12
Q

Which diseases occur from defects in cross-linking collagen?

A

Ehler-Danlos, Menkes

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13
Q

What is heterodisomy?

A

When a child inherits both sets of chromosomes from a single parent (both of their homologous chromosomes). Error in Meiosis I.

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14
Q

What is Isodosomy?

A

When a child inherits two identical copies of a single chromosome that duplicated itself from one parent. Error in meiosis II or postzygotic chromosomal duplication

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15
Q

What are the four assumptions for Hardy-Weinberg equilibrium?

A

No mutations
No natural selection
No net migration
Random mating

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16
Q

What is the formula for Hardy-Weinberg?

A

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

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17
Q

Describe the etiology of Prader-Willi syndrome

A

Maternal gene is imprinted (silenced). Paternal gene is deleted/mutated.

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18
Q

Clinical presentation of Prader-Willi Syndrome

A

Hyperphagia, obesity, retardation, hypogonadism, hypotonia

19
Q

Etiology of Angelman syndrome

A

Paternal gene imprinted (silenced). Deletion/mutation of maternal gene

20
Q

Clinical presentation

A

Inappropriate laughter, seizures, ataxia, severe intellectual disability

21
Q

Which chromosome is affected in Angelman and Prader-Willi syndrome?

A

Chromosome 15

22
Q

What is the cause of Prader-Willi syndrome in 25% of cases?

A

Maternal uniparental disomy (child inherits both silenced maternal genes)

23
Q

What is the defect in most autosomal dominant diseases?

A

Defective structural gene

24
Q

What is critical for diagnosing autosomal dominant disorder?

A

Family history

25
Q

How do mitochondrial myopathies present?

A

MELAS: mitochondrial encephalopathy, lactic acidosis, stroke-like episodes. Secondary to ox-phos failure.

26
Q

What biopsy result is key to diagnosing a mitochondrial disorder?

A

ragged red fibers

27
Q

What is the common cause of death in Duchenne Muscular Dystrophy?

A

Dilated Cardiomyopathy

28
Q

Which test s diagnostic for CF?

A

increased Cl- concentration (>60) in sweat

29
Q

What is the function of Dystrophin?

A

Anchors muscle fibers by connecting intracellular cytoskeleton (Actin) to transmembrane proteins (ECM)

30
Q

How are Duchenne Muscular Dystrophy and Becker Muscular Dystrophy inherited?

A

XLR

31
Q

How is Myotonic Type 1 dystropy inherited?

A

Autosomal dominant

32
Q

Etiology and presentation of Myotonic Type 1

A

CTG expansion of dystrophin. Myotonia, muscle wasting, cataracts, testicular atrophy, frontal balding, arrhythmia

33
Q

How is Fragile-X syndrome inherited?

A

XLD

34
Q

What is the mutation in Fragile X syndrome?

A

FMR1 gene mutation (decreased expression) due to CGG repeats.

35
Q

Clinical manifestation of Fragile X

A

2nd MCC of genetic intellectual disability. Large jaw, large everted ears, autism, mitral valve prolapse

36
Q

Which hematologic complications are Down Syndrome patients at risk for?

A

ALL and AML

37
Q

First-trimester ultrasound can detect Down syndrome via

A

increased nuchal translucency and hypoplastic nasal bone; decreased serum PAPP-A and increased free beta-hCG

38
Q

Second trimester quad screen for Down syndrome shows

A

decreased alpha-fetoprotein, increased beta-hCG, decreased estriol, increased inhibin A

39
Q

What is the rare chromosomal anomaly that causes Down syndrome in 4% of patients?

A

Robertsonian translocation between 14 and 21

40
Q

Which trisomy is Edwards syndrome

A

Trisomy 18

41
Q

What are the clinical features of Edwards syndrome?

A

Severe intellectual disability, rocker-bottom feet, small jaw, low-set ears, clenched hands with overlapping fingers, prominent occiput, congenital hear disease. Death within 1 year of birth

42
Q

What does a second-trimester quad screen for Edwards syndrome show?

A

decreased AFP, decreased beta-hCG, decreased estriol, decreased or normal inhibin A

43
Q

Which chromosomal abnormality is Patau syndrome?

A

Trisomy 13

44
Q

Clinical manifestation of Patau?

A

Severe intellecual disability, rockerbottom feet, small eyes, small head, cleft lip/palate, holoprosencephaly, polydactyly, congenital heart disease, cutis aplasia. Death within first year

USMLE (36 decks)

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