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Biochemestry > Genetics > Flashcards

Genetics Flashcards

1
Q

Most common cause of inherited intelectual disability and autism

A

Fragile X syndrome

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2
Q

Clinical findings in FXS

A
  1. Post-pubertal
  2. Macroorchidism
  3. Long face with large jaws
  4. Large everted ears
  5. Autism
  6. MVP
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3
Q

Gene affected in FXS and where is it

A

FMR1 in the long arm of the X chromosome

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4
Q

Trinucleotide repeat in FXS

A

CGG (“Chin giant gonads”)

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5
Q

When in cell division can trinucleotide repeats expand in FXS

A

Oocyte meiosis

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6
Q

How many repeats are needed for a full mutation in FXS

A

More tan 200

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7
Q

Genetic consequence of CGG trinucleotide repeat in FXS

A

Hypermethylation

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8
Q

Missing gene in Turner syndrome resulting in short stature

A

SHOX gene

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9
Q

Classic presentation in neurofibromatosis type 1

A
  1. Café-au-lait spots
  2. Lisch nodules (iris hamartomas)
  3. Cutaneous neurofibromas
  4. Pheochromocytomas
  5. Optic gliomas

*Can also present with bony abnormalitis such as congenital pseudoarthrosis

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10
Q

Inheritance pattern of neurofribromatosis type 1

A

Autosomal dominant

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11
Q

Affected gene on neurofibromatosis type 1

A

NF1 gene on chromosome 17

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12
Q

Define codominance

A

Both alleles contribute to the phenotype of the heterozygote

*eg, blood groups

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13
Q

Define variable expressivity

A

Patients with the same genotype have varying phenotypes

*eg, 2 pts with NF1 may have varying disease severity

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14
Q

Define incomplete penetrance

A

Not all individuals with a mutant genotype show the mutant phenotype

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

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15
Q

Define pleiotropy

A

When one gene contributes to multiple phenotypic effects

*eg, untreated PKU manifests with light skin, intellectual disability, and musty body odor

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16
Q

Define anticipation

A

Increased severity or earlier onset of disease in succeeding generations

*eg, trinucleotide repeat diseases

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17
Q

Define loss of heterozygosity

A

If a patient inherits or develops a mutation in a tumor supressor gene, the complementary allele must be deleted/mutated before cancer develops

*eg, retinoblastoma and the “2-hit hypothesis”, Lynch syndrome (HNPCC), Li-Fraumeni syndrome

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18
Q

Define a dominant negative mutation

A

When a heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning

*eg, mutation of a transcription factor in its allosteric site (nonfunctional mutant can still bind DNA, preventing wild-type transcription factor from binding)

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19
Q

Define linkage disequilibrium

A

Tendency for certain alleles at 2 linked loci to occur together more or less often than expected by chance

*Measured in a population

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20
Q

Define mosaicism

A

Presence of genetically distinct cell lines in the same individual

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21
Q

Define somatic mosaicism

A

When the mutation arises from mitotic errors after fertilization and propagates through multiple tissues or organs

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22
Q

Define gonadsl mosaicism

A

When the mutation appears only in egg or sperm cells

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23
Q

Pathogenesis of McCune-Albright syndrome

A

Mutation affecting G-protein signaling

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24
Q

Signs and symptoms of McCune-Albright syndrome

A

Triad:

  1. Café-au-lait spots with ragged edges (follow lines of Blashko)
  2. Polyostotic fibrous dysplasia
  3. At least 1 endocrinopathy (eg, precocious puberty)

*Survivable in patients with mosaicism

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25
Q

Define locus heterogeneity

A

Mutations in different loci can produce a similar phenotype (eg, albinism)

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26
Q

Allelix heterogeneity

A

Different mutations in the same locus produce the same phenotype (eg, beta thalassemia)

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27
Q

Define heteroplasmy

A

Presence of both normal and mutated mtDNA, resulting in variable expression of a mitochondrial disease

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28
Q

Define uniparental disomy

A

Offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent

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29
Q

Type of uniparental disomy that reflects an error in meiosis 1

A

Heterodisomy

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30
Q

Type of uniparental disomy that reflects an error in meiosis 2

A

Isodisomy

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31
Q

What is the Hardy-Weinberg equilibrium formula

A

p2 + 2pq + q2 and p

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32
Q

What is the Hardy-Weinberg equilibrium formula

A

p2 + 2pq + q2 and p + q = 1

  • P2 is the frequency of homozygosity for allele A
  • Q2 is the frequency if homozygosity for allele a
  • 2PQ is the frequency of heterozygosity
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33
Q

Affected chromosome in Prader-Willi and Angelman syndromes

A

Chromosome 15

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34
Q

Pathogenesis of Prader-Willi syndrome

A

Gene from mother is imprinted while the paternal gene is deleted/mutated

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35
Q

Signs and symptoms of Prader-Willi syndrome

A
  • Hyperphagia
  • Obesity
  • Intellectual disability
  • Hypogonadism
  • Hypotonia
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36
Q

Percentage of cases of Prader-Willi syndrome due to maternal uniparental disomy

A

25%

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37
Q

Pathogenesis of Angelman syndrome

A

Paternal gene is normally imprinted, and maternal gene is deleted/mutated

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38
Q

Signs and symptoms of Angelman syndrome

A
  • Inappropite laughter
  • Seizures
  • Ataxia
  • Severe intellectual disability
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39
Q

Percentage of cases of Angelman syndrome that are due to paternal uniparental disomy

A

5%

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40
Q

Mode of inheritance of hypophosphatemic rickets

A

X-linked dominant

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41
Q

Pathogenesis of hypophosphatemic rickets

A

Increased phosphate wasting at proximal tubule

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42
Q

Characteristic histopathologic finding seen in mitochondrial myopathies

A

Ragged red fibers

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43
Q

Signs and symptoms common to mitochondrial myopathies

A
  • Myopathy
  • Lactic acidosis
  • CNS disease
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44
Q

Mode of inheritance of cystic fibrosis

A

Autosomal recessive

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45
Q

Defective gene in cystic fibrosis

A

CFTR on chromosome 7

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46
Q

Most common mutation in cystic fibrosis

A

Deletion of Phe508 leads to misfolding of the protein and its retention in the RER

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47
Q

Normal function of the CFTR (abnormal protein in cystic fibrosis)

A

It is an ATP-gated Cl- channel that secretes Cl- in lungs and GI tract and reabsorbs Cl- in sweat glands

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48
Q

Pathogenesis of cystic fibrosis

A

Retained CFTR causes decreased Cl- and water secretion, leading to increased intracelular Cl- and compensatory increased Na reabsorption - This causes increased water reabsorption and abnormally thick mucus

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49
Q

Laboratory diagnosis of cystic fibrosis

A

Increased Cl- concentration (more tan 60 mEq/l) in sweat

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50
Q

Cystic fibrosis increases susceptibility to which bacterial infection

A

Pseudomonas aeruginosa

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51
Q

Cystic fibrosis increases resistance to which bacterial infection

A

Salmonella typhi

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52
Q

Complications that are usually seen in cystic fibrosis

A
  • Recurrent pulmonary infections, chronic sinusitis, and bronchiectasis
  • Pancreatic insufficiency
  • Infertility in men (abscence of vas deferens) and subfertility in women (thick cervical mucus)
  • Nasal polyps
  • Clubbing of the nails
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53
Q

Type of mutation commonly seen in Duchenne muscular dystrophy

A

Frameshift mutation (and nonsense)

*This leads to a truncated or absent dystrophin protein

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54
Q

Mutated protein in Duchenne muscular dystrophy

A

Dystrophin

*Largest protein-coding human gene, increases chance of spontaneous mutations

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55
Q

Mode of inheritance of Duchenne muscular dystrophy

A

X-linked

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56
Q

Signs and symptoms of Duchenne muscular dystrophy

A
  • Weakness of pelvic girdle muscles (progresses superiorly)
  • Onset before 5 years of age
  • Pseudohypertrophy of calf muscles (fibrofatty replacement)
  • Waddling gait (duck-like walk, trunk sways side to side with wide base of support)
  • Dilated cardiomyopathy (common cause of death)
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57
Q

Normal function of dystrophin

A

Anchors the actin cytoskeleton of muscle fibers to the transmembrane proteins alpha and beta dystroglycan, which are connected to the extracelular matrix

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58
Q

Laboratory findings seen in Duchenne muscular dystrophy

A

Increased CK and aldolase

*Loss of dystrophin results in myonecrosis

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59
Q

Type of mutation commonly seen in Becker muscular dystrophy

A

Non-frameshift deletions

60
Q

Mutated protein in Becker muscular dystrophy

A

Dystrophin

61
Q

Age of onset of Becker muscular dystrophy

A

Adolescence or early adulthood

62
Q

Muscular dystrophy caused by a CTG trinucleotide repeat

A

Myotonic type 1 muscular dystrophy

63
Q

Affected gene in myotonic type 1 muscular dystrophy

A

DMPK gene

*Abnormal expression of myotonin protein kinase

64
Q

Signs and symptoms of myotonic type 1 muscular tystrophy

A
  • Myotonia
  • Muscle wasting
  • Cataracts
  • Testicular atrophy
  • Frontal balding
  • Arrhythmia

– CTG: Cataracts, Toupee, Gonadalar atrophy

65
Q

Define the Gower sign

A

Patient uses upper extremities to help stand up

*Classically seen in Duchenne muscular dystrophy

66
Q

Trinucleotide repeat expansion disease in which there is increased number of repeats in an exon, coding for glutamine

A

Huntington disease

67
Q

Most important gastrointestinal associations in Down syndrome

A

Duodenal atresia and Hirschprung disease

68
Q

Most important cardiovascular association in Down syndrome

A

Endocardial cushion defects (atrioventricular septal defect)

69
Q

Ophthalmologic sign associated with Down syndrome

A

Brushfeld spots (White/gray discolorations in the periphery of the iris)

70
Q

Neurologic disease associated with Down syndrome

A

Early onset Alzheimer disease

*Chromosome 21 codes for amyloid precursor protein

71
Q

Common hematologic malignancies associated with Down syndrome

A

ALL and AML (M7)

72
Q

Most common etiology of Down syndrome

A

Meiotic nondisjunction in meiosis 1 (95% of cases)

73
Q

Percentage of cases of Down syndrome that are the result of an unbalanced Robertsonian translocation

74
Q

Most common chromosomes involved in a Robertsonian translocation leading to Down syndrome

75
Q

Diagnostic second trimester quad screen for Down syndrome

A
  • Low alpha fetoprotein
  • Low estriol
  • High beta hCG
  • High inhibin A
76
Q

Classical ultrasound characteristic seen in Down syndrome

A

High nucal translucency and hypoplastic nasal bone

77
Q

Signs and symptomes of Edwards syndrome

A

“PRINCE Edward”

  • Prominent occiput
  • Rocker-bottom feet
  • Intellectual disability
  • Nondisjunction
  • Clenched fists (with overlapping fingers)
  • low-set Ears
78
Q

Gastrointestinal abnormalities associated with Edwards syndrome

A
  • Meckel’s diverticulum

* Malrotation

79
Q

Renal abnormalities associated with Edwards syndrome

A

Horseshoe kidney

80
Q

Diagnostic quad screen for Edwards syndrome

A

Prince Edward is DOWN

  • Low alpha fetoprotein
  • Low beta hCG
  • Low estriol
  • Low (or normal) inhibin A
81
Q

Trisomy of which chromosome is seen in Edwards syndrome

82
Q

Trisomy of which chromosome is seen in Patau syndrome

83
Q

Signs and symptoms of Patau syndrome

A
  • Severe intelectual disability
  • Rocker-bottom feet
  • Microphthalmia
  • Microcephaly
  • Cleft lip/palate
  • HOLOPROSENCEPHALY
  • Polydactyly
  • Cutis aplasia
84
Q

Type of chromosome involved in Robertsonian translocations

A

Acrocentric chromosome (chromosomes with centromeres near their ends)

85
Q

Chromosomal abnormality seen in Williams syndrome

A

Microdeletion of the long arm of chromosome 7 (elastin gene)

86
Q

Signs and symptoms of Williams syndrome

A
  • Elfin facies
  • Intellectual disability
  • Hypercalcemia (increased sensitivity to vitamin D)
  • Well-developed verbal skills
  • Extreme friendliness with strangers
  • Cardiovascular problems
87
Q

Signs and symptoms of 22q11 deletion

A

“CATCH-22”

  • Cleft palate
  • Abnormal facies
  • Thymic aplasia leading to T cell deficiency
  • Cardiac defects (most important is tetrallogy of Fallot)
  • Hypocalcemia
88
Q

Syndromes associated to 22q11 deletion

A
  1. DiGeorge syndrome: thymic, parathyroid, and cardiac defects
  2. Velocardiofacial syndrome: palate, facial, and cardiac defects
89
Q

Aberrant development of which branchial pouches is associated with 22q11 deletion syndromes

A

3rd and 4th

90
Q

Characteristics of autosomal dominant inheritance

A
  • Disease observed in every generation
  • Males and females affected equally
  • Affected genes often structural genes
  • Often pleiotropic and variably expressive
91
Q

Characteristics of autosomal recessive inheritance

A
  • Disease skips generations
  • Males and females affected equally
  • Often due to enzyme deficiencies
  • Increased risk in consanguíneos families
92
Q

Characteristics of X-linked recessive inheritance

A
  • Males more than females
  • Skipped generations are commonly seen
  • Male-to-male transmission never seen
93
Q

Characteristics of X-linked dominant inheritance

A
  • Male-to-male transmission never seen
  • Heterozygous females are affected
  • Does not skip generations
94
Q

Characteristics of mitocondrial inheritance

A
  • Disease transmitted only from affected females
  • Both males and females affected
  • No offspring of the affected male affected
95
Q

Leading known cause of intelectual disability and pregnancy loss

A

Chromosome abnormalities

96
Q

Definition of karyotype

A

Display of 23 pairs of human chromosomes in typical somatic cells

97
Q

Chromosomal abnormality that results from fertilization of an ovum by 2 sperm cells

98
Q

Definition of a reciprocal translocation

A

Genetic material exchanged between non-homologous chromosomes

99
Q

Consequences of reciprocal translocation during gametogenesis

A
  • No clinical consequences for carrier

* Reproduction by carrier may cause partial trisomies or monosomies

100
Q

Consequences of reciprocal translocation in somatic cells

A

May lead to cancer if there is alteration of oncogenes or tumor supressor genes

101
Q

Name the types of chromosomal inversions

A
  • Paracentric (include the centromere)

* Pericentric (doesn’t include the centromere)

102
Q

Consequences of chromosomal inversions

A

Carriers usually unaffected but offspring may have small partial trisomy

103
Q

Chromosome structural abnormalities that result in Turner syndrome

A
  • Loss of ring X chromosome

* Isochromosome of long arm of X chromosome

104
Q

What is an isochromosome

A

When a chromosome has 2 copies of one arm but no copy of the other

105
Q

Mode of inheritance of achondroplasia

A

Autosomal dominant

106
Q

Affected gene in familial adenomatous polyposis

A

APC gene on chromosome 5q21

107
Q

Apart from adenocarcinoma of the colon, a mutation in the APC gene increases the risk for developing what other type of cancer

A

Adenocarcinoma of the duodenum and ampulla of Vater

108
Q

Mode of inheritance of hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome)

A

Autosomal dominant disorder

109
Q

Signs and symptoms of hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome)

A
  • Blanching skin lesions (telangiectasias of skin and mucosas)
  • Recurrent epistaxis
  • Skin discolorations
  • AVM
  • GI bleeding
  • Hematuria
  • Possible iron deficiency anemia
110
Q

Mode of inheritance of hereditary spherocytosis

A

Autosomal dominant

111
Q

Pathogenesis of hereditary spherocytosis

A

Defect in proteins ankyrin, spectrin, band 3, and protein 4.2 (all part of the cell membrane), leading to a spherical shape of the erythrocytes, which are removed from the bloodstream by splenic macrophages

112
Q

Signs and symptoms of hereditary spherocytosis

A
  • Splenomegaly
  • Hemolytic anemia
  • Jaundice
  • Pigmented gallstones
  • Increased MCHC
113
Q

Hereditary spherocytosis treatment

A

Splenectomy

114
Q

Mode of inheritance of Huntington’s disease

A

Autosomal dominant

115
Q

Affected gene in Huntington’s disease

A

HD gene in chromosome 4

116
Q

Affected protein in Huntington’s disease

A

Huntingtin

117
Q

Trinucleotide repeat expansion seen in Huntington’s disease

118
Q

Pathogenesis of Huntington’s disease

A

Degeneration of GABAergic neurons in the caudate nucleus leads to removal of inhibitory input in extrapiramidal circuit, resulting in chorea

119
Q

Signs and symptoms of Huntington’s disease

A
  • Chorea
  • Onset between ages 20 and 40
  • Personality changes
  • Dementia
120
Q

Mode of inheritance of multiple endocrine neoplasia (MEN) syndromes

A

Autosomal dominant

121
Q

Affected gene in multiple endocrine neoplasia (MEN) 1

A

MEN1 in chromosome 11, it is a tumor supresor gene

122
Q

Affected protein in multiple endocrine neoplasia (MEN) 1

123
Q

Multiple endocrine neoplasia (MEN) 1 associated tumors

A
  • Pituitary (prolactinomas or GH)
  • Pancreatic endocrine tumors (gastrinomas are the most common)
  • Parathyroid adenomas (most common presentation)
124
Q

Affected gene in multiple endocrine neoplasia (MEN) 2A and 2B

A

RET gene, which codes for a receptor tyrosine kinase in cells of neural crest origin (proto-oncogene)

125
Q

Multiple endocrine neoplasia (MEN) 2A associated tumors

A
  • Parathyroid hiperplasia or adenoma
  • Pheochromocytoma
  • Medullary thyroid carcinoma
126
Q

Multiple endocrine neoplasia (MEN) 2B associated tumors

A
  • Phecochromocytoma
  • Medullary carcinoma of the thyroid
  • Mucocutaneous neuromas
  • Patients have a marfanoid habitus
127
Q

Mode of inheritance of neurofibromatosis type 2

A

Autosomal dominant

128
Q

Affected gene in neurofibromatosis type 2

A

NF2 in chromosome 22 (tumor suppressor gene)

129
Q

Signs and symptoms of neurofibromatosis type 2

A
  • Bilateral acoustic neuromas
  • Neurofibromas
  • Café-au-lait spots
  • Increased risk for meningiomas and ependymomas
130
Q

Mode of inheritance of tuberous sclerosis

A

Autosomal dominant

131
Q

Affected gene in tuberous sclerosis

A

TSC1/TSC2 mutation on chromosome 16

132
Q

Signs and symptoms of tuberous sclerosis

A

“HAMARTOMAS”

  • Hamartomas in CNS, skin, and lungs
  • Angiofibromas (butterfly pattern in face)
  • Mitral regurgitation
  • Ash-leaf spots
  • Rhabdomyomas (cardiac)
  • (Tuberous sclerosis)
  • dÓminant
  • Mental retardation
  • Angiomyolipomas (renal)
  • Seizures
  • Shagreen patches
133
Q

Apart from hamartomas, tuberous sclerosis predisposes the patient to what other type of CNS and ungueal tumor

A

Subependymal giant cell astrocytoma and ungual fibroma

134
Q

Mode of inheritance of von Hippel Lindau syndrome

A

Autosomal dominant

135
Q

Affected gene in von Hippel Lindau syndrome

A

VHL gene on chromosome 3p

*Tumor suppressor gene whose main action is to tag proteins with ubiquitin for degradation (eg, hipoxia-inducible factor)

136
Q

Signs and symptoms of von Hippel Lindau syndrome

A

“HARP”

  • Hemangioblastomas in retina, brain stem, cerebellum, spine
  • Angiomatosis (cavernous hemangiomas) in skin, mucosa, and organs
  • Renal cell carcinomas (bilateral)
  • Pheochromocytomas
137
Q

Mode of inheritance of Friedrich ataxia

A

Autosomal recessive

138
Q

Affected gene in Friedrich ataxia

A

Frataxin gene, develops a GAA trinucleotide repeat on chromosome 9

139
Q

Signs and symptoms of Friedrich ataxia

A
  • Gait ataxia (pes cavus, hammer toes)
  • Dysarthria
  • Hand clumsiness
  • Loss of sense of position
  • Impaired vibratory sensation
  • Arreflexia in all 4 limbs
  • Diabetes mellitus
  • Hypertrophic cardiomyopathy
140
Q

Pathogenesis of Friedrich ataxia

A

Frataxin is essential for mitochondrial iron regulation, in its absence, mitochondrial iron builds up, leading to free radical damage and mitochondrial dysfunction

141
Q

Only trinucleotide repeat expansion disease that appears in exons and actually codes for an aminoacid

A

Huntington’s disease, CAG codes for glutamine

142
Q

Sequence of events in disjunction during meiosis 1

A
  1. Homologue chromosomes pair with each other at metaphase plate
  2. During anaphase 1, homologues disjoin
  3. At the end of meiosis 1, each daughter cell has 1 homolog
143
Q

Sequence of events in disjunction during meiosis 2

A
  1. During metaphase 2, each chromosome aligns individually at the metaphase plate
  2. In anaphase 2, sister chromatids migrate to opposite poles
  3. At the end of meiosis 2, each daughter cell has 1 chromatid
144
Q

Normal function of the NF1 gene product

A

Inhibit p21/RAS oncoprotein

145
Q

Most common trisomy among miscarriages

A

Trisomy 16

Biochemestry (7 decks)

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