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USMLE® Step 1 > USMLE (S1) Biochemistry > Biochem - Genetics (Part 1) > Flashcards

Biochem - Genetics (Part 1) Flashcards

1
Q

Approximately what percentage of individuals with von Hippel-Lindau disease will develop bilateral renal cell carcinomas?

A

50%

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2
Q

The vascular tumors of von Hippel-Lindau disease are commonly seen in which parts of the nervous system?

A

Retina, cerebellum, medulla

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3
Q

What is the pathophysiology of von Hippel-Lindau disease?

A

A tumor suppressor is deleted, leading to constitutive expression of hypoxia-inducible factors and an overabundance of vascular growth factors

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4
Q

The defect that leads to von Hippel-Lindau disease is found on chromosome _____.

A

3 (remember: Von Hippel-Lindau = 3 words for chromosome 3)

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5
Q

What is the mode of inheritance of albinism?

A

Autosomal recessive

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6
Q

What is the mode of inheritance of 1 antitrypsin deficiency?

A

Autosomal recessive

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7
Q

What is the mode of inheritance of phenylketonuria?

A

Autosomal recessive

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8
Q

What is the mode of inheritance of the thalassemias?

A

Autosomal recessive

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9
Q

What is the mode of inheritance of sickle cell disease?

A

Autosomal recessive

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10
Q

What is the mode of inheritance of the glycogen storage diseases?

A

Autosomal recessive

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11
Q

What is the mode of inheritance of most mucopolysaccharidoses?

A

Autosomal recessive

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12
Q

Most mucopolysaccharidoses are inherited in a(n) _____-_____ pattern, except for _____ _____.

A

Autosomal-recessive; Hunter’s disease

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13
Q

Most sphingolipidoses are inherited in a(n) _____-_____ pattern, except for _____ _____.

A

Autosomal-recessive, Fabry’s disease

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14
Q

What is the mode of inheritance of hemochromatosis?

A

Autosomal recessive

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15
Q

What is the pattern of inheritance of cystic fibrosis?

A

Autosomal recessive

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16
Q

Cystic fibrosis results from a defect in which gene? Which chromosome? Which ion channel?

A

CFTR; 7; chloride

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17
Q

Patients with cystic fibrosis characteristically have mucus plugs that disturb the function of which three organs?

A

The pancreas, the lungs, and the liver

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18
Q

Which two pathogens are the most likely to cause recurrent pulmonary infections in a patient with cystic fibrosis?

A

Pseudomonas species and Staphylococcus aureus

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19
Q

Recurrent pulmonary infections in patients with cystic fibrosis result in what pulmonary pathology?

A

Bronchiectasis

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20
Q

An infant with failure to thrive also had meconium ileus as a newborn. What is the most likely diagnosis?

A

Cystic fibrosis

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21
Q

How is cystic fibrosis diagnosed?

A

High concentrations of chloride ions in the sweat

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22
Q

A male patient with cystic fibrosis asks you whether he will be able to have children; what is your response?

A

Unfortunately, males with cystic fibrosis are infertile due to bilateral absence of the vas deferens

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23
Q

A patient with cystic fibrosis is at increased risk for the deficiency of what four vitamins?

A

Vitamins A, D, E, and K, all of which are fat soluble

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24
Q

What is the most common lethal genetic disease among Caucasians?

A

Cystic fibrosis

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25
Q

Treatment with what drug helps to loosen mucous plugs in patients with cystic fibrosis?

A

N-acetylcysteine

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26
Q

How does N-acetylcysteine free up mucous plugs?

A

It cleaves the disulfide bonds that connect mucous glycoproteins

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27
Q

What is the pattern of inheritance of fragile X syndrome?

A

X-linked dominant (remember: Be Wise, Fool’s GOLD Heeds False Hope; Fragile X)

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28
Q

What is the pattern of inheritance of Duchenne’s muscular dystrophy?

A

X-linked recessive (remember: Be Wise, Fool’s GOLD Heeds False Hope; Duchene)

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29
Q

What is the pattern of inheritance of hemophilia A and B?

A

X-linked recessive (remember: Be Wise, Fool’s GOLD Heeds False Hope; Hemophilia A)

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30
Q

What is the pattern of inheritance of Fabry’s disease?

A

X-linked recessive (remember: Be Wise, Fool’s GOLD Heeds False Hope; Fabry’s)

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31
Q

What is the pattern of inheritance of glucose-6-phosphate dehydrogenase deficiency?

A

X-linked recessive (remember: Be Wise, Fool’s GOLD Heeds False Hope; Glucose-6-phosphate dehydrogenase)

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32
Q

What is the pattern of inheritance of Hunter’s syndrome?

A

X-linked recessive (remember: Be Wise, Fool’s GOLD Heeds False Hope; Hunter’s)

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33
Q

What is the pattern of inheritance of ocular albinism?

A

X-linked recessive (remember: Be Wise, Fool’s GOLD Heeds False Hope; Ocular albinism)

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34
Q

What is the pattern of inheritance of Lesch-Nyhan syndrome?

A

X-linked recessive (remember: Be Wise, Fool’s GOLD Heeds False Hope; Lesch-Nyhan)

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35
Q

What is the pattern of inheritance of Bruton’s agammaglobulinemia?

A

X-linked recessive (remember: Be Wise, Fool’s GOLD Heeds False Hope; Bruton’s agammaglobulinemia)

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36
Q

What is the pattern of inheritance of Wiskott-Aldrich syndrome?

A

X-linked recessive (remember: Be Wise, Fool’s GOLD Heeds False Hope; Wiskott-Aldrich)

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37
Q

True or False? Hunter’s syndrome has the same pattern of inheritance as Hurler’s syndrome.

A

False; Hunter’s syndrome has X-linked recessive inheritance, whereas Hurler’s syndrome has autosomal-recessive inheritance

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38
Q

Why are female carriers of X-linked recessive disorders rarely affected?

A

There is random inactivation of X chromosomes in each cell, a process known as lyonization

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39
Q

Duchenne’s muscular dystrophy is caused by a deletion of what gene?

A

The dystrophin gene (remember: Duchenne’s = Deleted Dystrophin)

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40
Q

Is the loss of the dystrophin gene in Duchenne’s muscular dystrophy the result of frameshift, missense, nonsense, or silent mutations?

A

Frameshift mutation

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41
Q

What is the pathophysiology of Duchenne’s muscular dystrophy?

A

Dystrophin anchors muscle fibers in the membrane and lack of the protein leads to accelerated muscle breakdown

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42
Q

At what age do Becker’s and Duchenne’s muscular dystrophy present?

A

Before the age of 5 years

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43
Q

In what muscle group does weakness normally begin in patients with Duchenne’s muscular dystrophy?

A

The pelvic girdle muscles

44
Q

A 4-year-old boy needs to use his upper extremities to push against his legs in order to stand up. What is the name of this maneuver?

A

Gower’s maneuver; the action is necessary due to the weakness of the proximal muscles

45
Q

A 4-year-old boy with Duchenne’s muscular dystrophy has hypertrophied calf muscles; what is the expected strength in his legs?

A

This is actually pseudohypertrophy due to fibrofatty replacement of the muscle and you would expect muscle weakness

46
Q

What organ other than skeletal muscle is affected in Duchenne’s muscular dystrophy?

A

Heart

47
Q

What aspect of the dystrophin gene makes it particularly susceptible to mutation?

A

The dystrophin gene (DMD) is the largest known human gene, which allows a high rate of spontaneous mutations

48
Q

Is Becker’s muscular dystrophy more or less severe than Duchenne’s muscular dystrophy?

A

Becker’s muscular dystrophy is less severe and presents later in life

49
Q

How is muscular dystrophy diagnosed?

A

Biopsy of skeletal muscle and elevated creatine phosphokinase

50
Q

Fragile X syndrome is caused by a defect in which gene?

A

FMR1 ; the name of the gene stands for Familial Mental Retardation

51
Q

What are the two most common genetic causes of mental retardation?

A

Down syndrome and fragile X syndrome

52
Q

A male patient has a long face, a large jaw, large ears, autism, and macroorchidism. What is the most likely diagnosis?

A

Fragile X syndrome (remember: Fragile X = eXtra large testes, jaw, ears)

53
Q

What triplet is expanded in fragile X syndrome and what is the result of this repeat?

A

CGG; abnormal methylation of the FMR1 gene

54
Q

True or False? Fragile X syndrome is associated with chromosomal breakage.

A

TRUE

55
Q

Name four diseases that result from trinucleotide repeat expansion.

A

Huntington’s disease, myotonic dystrophy, Friedreich’s ataxia, Fragile X syndrome (remember: Try (trinucleotide) hunting for my fried eggs [X])

56
Q

What does anticipation refer to in genetic disease?

A

Anticipation involves an increase in disease severity and an earlier age of onset in successive generations

57
Q

Myotonic dystrophy is associated with a _____ (CTG/CGG) repeat, while fragile X syndrome has a _____ (CTG/CGG) repeat.

A

CTG; CGG (remember: myoTonic dystrophy = CTG, fraGile X = CGG)

58
Q

Huntington’s disease has a _____ repeat, while Friedreich’s ataxia is a repeat of _____ nucleotides.

A

CAG; GAA

59
Q

A patient has a flat facial profile, prominent epicanthal folds, and a simian crease. This patient also has mental retardation. What is the most likely diagnosis?

A

Down syndrome

60
Q

A newborn is diagnosed with Down syndrome. She is vomiting bilious material. What is the most likely cause?

A

Duodenal atresia

61
Q

A newborn is diagnosed with Down syndrome. He has a heart murmur on examination. What is the most likely cause?

A

Atrial septal defect

62
Q

What type of atrial septal defect is most common in patients with Down syndrome?

A

Septum-primum type

63
Q

What is the most common chromosomal disorder?

A

Down syndrome

64
Q

Patients with Down syndrome who are more than 35 years old have an increased risk of what neurodegenerative disease?

A

Alzheimer’s disease

65
Q

Patients with Down syndrome have an increased risk of what type of leukemia?

A

Acute lymphocytic leukemia

66
Q

Ninety-five percent of cases of Down syndrome are caused by the _____ of homologous chromosomes during the cell division process of _____.

A

Nondisjunction; meiosis

67
Q

What is the likelihood of a 20-year-old woman having a baby with Down syndrome? A 45-year-old woman?

A

1:1500; 1:25

68
Q

What is the most common genetic mechanism leading to Down syndrome?

A

Meiotic nondisjunction

69
Q

What results in the prenatal quad screen indicate possible Down syndrome?

A

-fetoprotein-human chorionic gonadotropin, estriol, and inhibin A

70
Q

Down syndrome is also known as trisomy _____.

A

21 (remember: Drinking age = 21)

71
Q

Which trisomy is the most common: 13, 18, or 21? What is the least common?

A

21 (1:700); 13 (1:15,000)

72
Q

What is the other name for trisomy 18?

A

Edwards; syndrome (remember: Election age = 18)

73
Q

What are the clinical features of trisomy 18?

A

Mental retardation, rocker-bottom feet, micrognathia, low-set ears, clenched hands, prominent occiput, congenital heart disease

74
Q

What is the prognosis for a patient with trisomy 18?

A

Death within the first year of life

75
Q

A baby has low-set ears, micrognathia, a prominent occiput, rocker bottom feet, and clenched hands. What is the most likely diagnosis?

A

Edwards’ syndrome (trisomy 18)

76
Q

A newborn has microphthalmia, microcephaly, cleft lip, cleft palate, and polydactyly. What is the most likely diagnosis?

A

Patau’s syndrome (trisomy 13)

77
Q

Patau’s syndrome is also known as trisomy _____.

A

13 (remember: Puberty = 13)

78
Q

What are the clinical manifestations of trisomy 13?

A

Severe mental retardation, rocker-bottom feet, microphthalmia, microcephaly, cleft lip/palate, holoprosencephaly, polydactyly, congenital heart disease

79
Q

True or False? Newborns with trisomy 13 and newborns with trisomy 18 have similar expected life spans.

A

True; infants with both of these conditions are expected to die before the age of 1 year

80
Q

The life expectancy for patients with trisomy 21 is _____ (1 year/20-40 years/45-50 years).

A

45-50 years

81
Q

What is a Robertsonian translocation?

A

It is a nonreciprocal translocation of chromosome pairs, such that chromosomes carry genetic information in an uneven manner

82
Q

What makes chromosomes 13, 14, 15, 21, and 22 candidates for Robertsonian translocations?

A

They are acrosomal chromosomes, which means that the centromere is located near one end rather than in the middle

83
Q

How do acrosomal chromosomes align to create a Robertsonian translocation?

A

The long arms match up and fuse at the centromere, losing the short arms of the chromosomes

84
Q

Does a Robertsonian translocation always result in a loss of genetic material?

A

A balanced translocation retains all genetic material and will not have any abnormal phenotype; if the translocation is unbalanced, genetic material is lost and abnormalities result

85
Q

True or False? An unbalanced Robertsonian translocation may cause a chromosomal imbalance, but rarely miscarriage or stillbirth.

A

False; unbalanced translocations may result in miscarriage, stillbirth, or chromosomal imbalance such as Down or Patau’s syndrome

86
Q

The two types of chromosomal inversions are called _______ and _____inversions.

A

Pericentric and paracentric

87
Q

In chromosomal inversions, _____ (pericentric/paracentric) inversion involves the centromere and proceeds through meiosis.

A

Pericentric

88
Q

In chromosomal inversions, _____ (pericentric/paracentric) inversion does not involve the centromere and does not proceed through meiosis.

A

Paracentric

89
Q

How does a chromosomal inversion modify the affected chromosome?

A

It reverses one segment of the chromosome end-to-end

90
Q

The deletion of the short arm of chromosome 5 leads to what disease?

A

Cri-du-chat syndrome

91
Q

A newborn has microcephaly and epicanthal folds and produces a high-pitched crying or mewing sound. What is the most likely diagnosis?

A

Cri-du-chat syndrome

92
Q

What are the clinical manifestations of cri-du-chat syndrome?

A

Microcephaly, moderate to severe mental retardation, high-pitched crying/mewing, epicanthal folds, cardiac abnormalities

93
Q

Cri-du-chat syndrome is caused by a deletion of the _____ arm of chromosome ____.

A

Short; 5

94
Q

What disease is caused by a microdeletion of the long arm of chromosome 7?

A

Williams syndrome

95
Q

Among others, what connective tissue gene is deleted in Williams syndrome?

A

The elastin gene

96
Q

Patients with Williams syndrome typically have _____ (coarse/masked/elfin) facies.

A

Elfin

97
Q

A patient has an extreme friendliness towards strangers and cheerful disposition, with noted mental retardation and cardiovascular disease; what is the diagnosis?

A

Williams syndrome

98
Q

In spite of their mental retardation, in which cognitive area are patients with Williams syndrome typically advanced?

A

Patients with Williams syndrome typically have well-developed verbal skills

99
Q

Microdeletions at chromosome 22q11 can present as a spectrum of diseases including which two recognized syndromes?

A

DiGeorge syndrome or velocardiofacial syndrome

100
Q

What disease is caused by microdeletions at 22q11 and involves defects of the thymus, the parathyroid, and the heart?

A

DiGeorge syndrome

101
Q

What disease is caused by microdeletions at 22q11 and involves defects of the palate, the face, and the heart?

A

Velocardiofacial syndrome

102
Q

True or False? 22q11 Syndromes are associated with B cell deficiency.

A

False; 22q11 syndromes are associated with T lymphocyte deficiency due to thymic aplasia

103
Q

True or False? 22q11 Syndromes are associated with hypercalcemia.

A

False; 22q11 syndromes are associated with hypocalcemia due to parathyroid aplasia

104
Q

Name 5 findings associated with 22q11 deletion syndromes.

A

Cleft palate, Abnormal facies, Thymic aplasia, Cardiac defects, Hypocalcemia (remember: CATCH-22)

105
Q

What embryonic structures are altered in 22q11 syndromes?

A

These syndromes are due to aberrant development of the third and fourth branchial pouches

106
Q

True or False? 22q11 Syndromes are X-linked recessive and show anticipation.

A

False; 22q11 syndromes are due to microdeletions on chromosome 22 and have variable presentations

USMLE (S1) Biochemistry (9 decks)

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