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Pathology Exam 1 > Genetics > Flashcards

Genetics Flashcards

1
Q

What % of spontaneous abortions during early gestation (1st trimester) have a chromosomal abnormality?

A

50%

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2
Q

What is a mutation?

A

Permanent change in DNA

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3
Q

What are genome mutations?

A

Loss or gain of whole chromosomes

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4
Q

What are gene mutations?

A

Gives rise to visible structural changes in the chromosomes

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5
Q

What are the diff kinds of point mutations within a coding sequence?

A
  • Missense (alter meaning of code)
  • Nonsense (stop codon)
  • Frameshift (3 codons -> catastrophic results)
  • Silent
  • Nonsense + frameshift are the most destructive
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6
Q

What are tri-nucleotide (3 codons) repeat mutations?

A
  • When you have too many copies of a certain nucleotide triplet (caused by an increased # of CAG repeats)
  • Fragile X: involved gene is FMR-1
    • 2nd most common cause of genetic mental retardation (Down Syndrome = 1st)
    • Marco-orchidism (large testes), large everted ears, autism, MVP = symptoms
  • Huntington’s disease
  • Myotonic dystrophy
  • Friedreich’s ataxia
  • Usually cause neurological disorders
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7
Q

What is imprinting?

A

At a single locus (area) only 1 allele is active, the other is inactive (imprinted/inactivated by methylation)

  • Only one working copy is inherited w/ imprinting
  • Deletion of the active allele -> disease
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8
Q

What are 2 disease from imprinting?

A
  1. Prader-Willi syndrome
    • Deletion of normally active paternal allele
    • Mental retardation, hyperphagia, obesity, hypo-gonadim, hypotonia
  2. Angelman’s syndrome
    • Deletion of normally active maternal allele
    • Mental retardation, seizures, ataxia, inappropriate laugher (“happy puppet”)
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9
Q

Explain the percentages in a punnet square

A

AA = dominant gene = 25%

Aa = carriers (heterozygous) = 50%

aa = homozygous carriers (recessive) = 25%

  • percentages stay the same for every child
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10
Q

What is variable penetrance?

A

Even heterozygous can show some disease

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11
Q

What are the 5 modes of inheritance?

A
  1. Autosomal dominant
  2. Autosomal recessive
  3. X-linked recessive
  4. X-linked dominant
  5. Mitochondrial inheritance
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12
Q

How can you tell from a family pedigree that a disease is autosomal dominant? Autosomal recessive?

A
  • Dominant = see the disease in every generation
  • Recessive = skips generations
  • Every line in the tree represents a generation
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13
Q

What are characteristics of autosomal (non-sex) dominant disorders?

A

Changes to non-enzymatic proteins involved in regulation of complex metabolic pathways that are subject to feedback inhibition

  • Seen in every generation
  • Females + Males affected
  • Only need 1 copy of gene to have disorder/trait
  • Often pleotropic (1 gene has more than 1 effect on individual’s phenotype)
  • Presents clinically after puberty
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14
Q

A parent with an autosomal dominant disorder has what % chance of giving it to their offspring (for each pregnancy)?

A

50%

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15
Q

What is the mnemonic for Autosomal Dominant disorders?

A

Very Powerful DOMINANT Humans

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16
Q

What are characteristics of autosomal (non-sex) recessive disorders?

A

Change in enzymatic proteins (often loss of fx)

  • Can skip generations, due to carrier state
  • Parents often present in childhood
  • You need 2 copies of gene to have trait or disease
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17
Q

What are some autosomal recessive disorders?

A
  • Tay-Sachs
  • Albinism
  • ARPKD
  • Cystic fibrosis
  • Sickle cell anemia
  • Glycogen storage diseases
  • Hemochromatosis
  • Mucopolysaccharidoses (except Hunter’s)
  • Phenylketonuria (PKU)
  • Sphingolipidoses (except Fabry’s)
  • Thalessemias
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18
Q

What is Cystic Fibrosis?

A

Defect in CFTR gene -> affects cAMP pathway -> Cl- channel disorder -> affects mostly lungs, also pancrease, liver, kidneys, intestine

  • More viscous mucous -> difficulty breathing/frequent lung infx
  • 1/3200 live births
  • Most common lethal genetic disease in caucasians (N. Euros)
  • No known cure
  • Autosomal recessive
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19
Q

What is the 1st sign of cystic fibrosis?

A

Bowel obstruction due to meconium ileus (while baby eats in belly, meconium is the 1st poop of baby’s bowel - it can get thick and cause obstruction)

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20
Q

What does cystic fibrosis lead to?

A
  • Mucous plugging/infx (pseudomonas)
  • Pancreatic insufficiency
  • Increased sodium chloride in sweat (Cl sweat test)
  • Can develop infertility
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21
Q

What is sickle-cell anemia?

A

Hereditary, multi-sx disorder who cardinal features are hemolytic anemia + recurrent pain

  • Chronic hemolytic disease
  • Primarily in african-amer pop
  • Mis-shaped, sickled RBCs become trapped in small capillaries/block circulation -> vaso-occlusive crises -> extreme pain in chest/bones/abdomen
  • Autosomal recessive
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22
Q

What is sickle cell disease vs sickle cell trait?

A
  • Disease = homozygous (both copies of mutated beta gene)
  • Trait = heterozygous (1 copy of mutated gene)
    • 10% african-amer have sickle cell trait
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23
Q

What is phenylketonuria (PKU)?

A

Inborn error of metabolism (enzymatic mutation)

  • No phenylalanine hydroxylase -> can’t convert to tyrosine
  • Must avoid phenylalanine in diet (which is in all foods containing protein)
  • 1/12,000 caucasians
  • Autosomal recessive
  • Affects brain development (increase chance of seizures, mental retardation, autism)
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24
Q

What are clinical features of PKU?

A
  • Initially healthy newborns
  • Few weeks develop brain impairement
  • 6 mos severe mental retardation
  • Seizures, decreased pigmentation of hair/skin
  • “Mousy” or musty odor in breath, skin, or urine
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25
Q

What is galactosemia?

A

Inborn error of galactose metabolism (enzymatic mutation)

  • Lacking galactose-1-phosphate uridyltransferase
  • 1/60,000
  • Autosomal recessive
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26
Q

What are clinical features of galactosemia?

A
  • Born normal then fail to thrive
  • Liver - jaundice, liver damage
  • Ocular - cataracts
  • GI - vomiting, diarrhea
  • E. coli sepsis
  • Neurologic impairement
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27
Q

What do lysosomes contain?

A

Hydrolytic enzymes necessary for intracellular digestion

28
Q

What are sphingolipidosis?

A

Storage diseases characterized by abnormal storage of sphingolipids

29
Q

What are lysosomal storage diseases?

A
  • 40 lysosomal storage disorders
  • Autosomal recessive
  • Infants and young children
  • Cellular dysfunction
    • Hepatosplenomegaly
    • CNS involved
30
Q

What is Tay Sachs?

A
  • Lysosomal storage disease (type of gangliosidoses)
    • Gm2 gangliosides
  • Lack of lysosomal hexosaminidase A
  • CNS
  • Autosomal recessive
    • Chromosome 15
  • Common is Ashkenazi Jews (Carriers 1/30)
31
Q

What are clinical features of Tay Sachs?

A
  • Neurodegenerative
  • Motor weakness by 3-6 months of age
  • Severe mental retardation
  • Blindness
  • Cherry red spot in eyes
  • Death usually by 4-5 yrs
32
Q

What is Niemann-Pick Disease?

A

Inability to metabolize sphingomyelin (lacking sphingmyelinase)

  • Accumulation of lipid in phagocytic cells/neurons
  • Autosomal recessive
  • Lysosomal storage disease
33
Q

What are clinical features of Niemann-Pick disease?

A
  • Spleno + hepatomegaly
  • Affects lungs, bone marrow and lymph nodes
  • Neuronal damage -> severe neurologic deterioration
34
Q

What are the 4 different types of Niemann-Pick disease?

A
  • Type A = infants, death within 3 years of life (worst)
  • Type B = pre-teen yrs, no neuro involvement (able to live w/)
  • Type C + D = mix of both, difficulty in walking/swallowing, progressive loss of vision/hearing
35
Q

What is Gaucher disease?

A
  • Most common lysosomal storage disease
  • Inability to metabolize glucosylceramide (no glucocerebrosidase)
  • Autosomal recessive
  • Ashkenazi Jews (carrier 1/12)
  • Affects phagocytes + accumulates in liver, spleen, bone marrow + less commonly brain
36
Q

What are the clinical features of Gaucher disease?

A
  • Pancytopenia, splenomegaly, osteopenia, bone lesions, bone pain
    • Anemia, low platelets, bruise easily
  • Tx: enzyme replacement therapy and bone marrow transplantation
37
Q

What are the different types of Gaucher disease?

A
  • Type 1: No brain involvement, splenohepatomegaly, skeletal disorders
  • Type 2: 3 mos old - brain damage, death by 2 yrs
  • Type 3: Infantile type, splenohepatomegaly variable, brain involvement (seizures)
38
Q

What are x-linked recessive disorders?

A
  • Males are hemizygous (1 copy present)
  • Females have 2 X’s, males have 1 X (very rarely affects woman)
  • All daughters are carriers
  • Heterozygous females express disorder partially (variable penetrance b/c of 1 X)
  • NO male-to-male transmission
39
Q

What are exs of X-linked recessive disorders?

A
  • Brutons’ agammaglobulinemia
  • Wiskott-Aldrich syndrome
  • Fabyr’s disease
  • G6PD deficiency
  • Ocular albinism
  • Lesch-Nyhan syndrome
  • Duchene and Becker’s muscular dystrophy
  • Hunter’s syndrome
  • Hemophilia A and B
40
Q

What is G6PD deficiency?

A
  • X-linked recessive
  • Most individuals asymptomatic
  • Symptomatic pts usually male
  • ~400 known mutations in the gene coding for G6PD
  • Prolonged neonatal jaundice seen in a newborn
  • Hemolytic crisis in response to:
    • Ilness
    • Certain drugs, food (fava beans), chemicals
  • Diabetic ketoacidosis
41
Q

What are X-linked Dominant disorders?

A
  • Only given through X gene and not Y
  • Usually affects males worse b/c only have 1 X gene
  • Rare!!
  • Transmitted through both parents
  • ex: Vitamin D-resistant rickets
42
Q

What are mitochondrial diseases?

A

A group of genetic disorders that are caused by dysfunctional mitochondria (maternal inheritance)

  • Unique characteristics b/c mito = critical to cell fx
  • Mitochondrial myopathy = subclass that has neuromuscular disease sx
  • Sx are worse when diseased mito present in muscles, cerebrum or nerves
  • Sx: poor growth, loss of muscle coordination, muscle weakness, visual problems, hearing problems, learning disabilites, heart disease, liver disease, kidney disease, GI disorders, respiratory disorders, neurological problems, autonomic dysfunction, dementia
43
Q

What are Autosomal Trisomies?

A
  • Down Syndrome: Trisomy 21
  • Edwards’ Syndrome: Trisomy 18
  • Patau’s Syndrome: Trisomy 13
44
Q

What is Trisomy 21?

A

Down Syndrome (chromosomal/cytogenic disease)

  • Most common
  • 47 chromosomes
    • Aneuploidy: meiotic non-disjunction (when chromosomes do not separate -> have 3 of those chromosomes - 2 from 1 parent + 1 from other)
  • Other type: mosaicism, unbalanced translocation (uncommon)
45
Q

What is associated w/ higher risk of down syndrome?

A

Maternal age

  • 1/1550 live births -> under 20 yrs
  • 1/25 -> older than 45 yrs
46
Q

What are clinical features of Down syndrome?

A
  • Epicanthic fold (above the lip)
  • Flat facial profile
  • Simian crease
  • Tongue protrusion
  • A degree of mental retardation (varies)
  • Congenital malformations: cardiovascular + GI/GU
47
Q

What is mosaicism?

A

Accounts for about 1% of down syndrome cases

  • Nondisjunction of chromosome 21 takes place in 1 (but not all) of initial cell divisions after fertilization -> mixture of 2 types of cells (some containing usual 46 chromosomes, and others 47)
  • Cells w/ 47 chromsomes contain an extra chromosome 21
48
Q

What is translocation?

A

4% of all cases of Down’s

  • Part of chrom 21 breaks off during cell divison + attaches to other chromosome (typically chrom 14)
  • Total # of chrom remain 46, presence of an extra part of chrom 21 causes characteristics of Down’s
49
Q

What is Trisomy 18?

A

Edward’s syndrome

  • Types: mosaiciam + translocations
  • 1/3,000 live births, w/ a maternal age effect
  • Most fetuses are miscarried before term OR baby is stillborn
  • Diseases affecting the larger chromosomes have potential to be more catastrophic
    • 80% female
    • 30% die within a month of birth
    • 10% beyond 1 year, w/ profound learning disabilities
50
Q

What are clinical features of Edward Syndrome?

A
  • Clenched hands w/ overlapping fingers
  • Crossed legs
  • Rocker-bottom feet
  • Low birth weight
  • Low-set ears
  • 10-20% risk of acute leukemia
  • Mental deficiency
  • Microcephaly
  • Micrognathia (small tongue)
  • Congenital abnormalities of heart/kidneys
51
Q

What is Trisomy 13?

A

Patau syndrome

  • Chromosome 13 presents 3 times instead of 2
  • 4% w/ unknown outcomes are likely to result in a live birth
52
Q

What is Klinefelter Syndrome?

A

Affects male patients 47, XXY (they have more than one X)

  • XXXY, XXXXY
  • 1:1000
  • Most common cause of hypogonadism in males
  • Non-disjunction, mosaicism
  • The more X’s, the more severe
53
Q

What are clinical features of Klinefelter Syndrome?

A
  • Tallness w/ extra long arms and legs, short trunk
  • Gynecomastia (man boobs)
  • Lack of facial/body hair
  • Hypogonadism and small penis
  • Infertility
  • Social/learning disabilities
  • Normal -> borderline IQ
54
Q

What is Turners Syndrome?

A

45, X

  • Monosomy of the X chromosome
  • Affects only females (will only have one X chromosome instead of 2)
55
Q

What are clinical features of Turners?

A
  • Short stature
  • Web neck
  • Low hairline
  • Cubus Valgus
  • Shield chest
  • Primary amenorrhea…streak ovaries (ovaries aren’t working -> will not menstruate)
  • Coarctation of aorta (aorta dividing into 2)
56
Q

Marfan Disease, Ehlers-Danlos syndrome, and Osteogenesis Imperfecta are all defects in?

A

Structural proteins

57
Q

What is Marfan’s Syndrome?

A

Fibrillin gene mutation, affects skeleton/heart/eyes

  • Tall w/ long extremities, pectus carinatum, hyper-extensive joints, long fingers/toes (arachnodactyly), subluxation of lenses
  • Cystic medial necrosis of aorta -> incompetence + dissecting aortic aneurysm
58
Q

What is Ehlers-Danlos Syndrome?

A

Faulty collagen synthesis -> hyperextensive skin, tendency to bleed, hypermobile joints

  • Inheritance/severity varies
  • Can develop berry aneurysm or organ rupture
59
Q

What is Osteogenesis Imperfecta?

A

Genetic brittle bone disease

  • Most common form is autosomal dominant (AD) w/ abnormal Type 1 collagen
  • Multiple fxs w/ minimal trauma due to brittle bones
  • Blue sclerae due to translucency of CT over choroid
  • Hearing loss
  • Lack of dentin (dental imperfections)
60
Q

What is familial hypercholesterolemia?

A

Defect in receptor protein (mutation in gene encoding LCL receptor)

  • Loss of feedback control -> elevated cholesterol
  • Heterozygotes: 2-3x elevation in plasma cholesterol
    • Tendinous xanthomas + premature atherosclerosis
  • Homozygotes: 5-6x elevation in plasma cholesterol
    • SKin xanthomas, cerebral/peripheral atherosclerosis at early age
    • Can have MI before age of 20
  • Tx: statins (inhibit HMG CoA reductase -> greater synthesis of LDL receptors)
61
Q

What is a Robertsonian Translocation?

A

Non-reciprocal chromosomal translocation that commonly involves chromosome pairs 13, 14, 15, 21, and 22

  • Occurs when long arms of 2 acrocentric chromosomes (chromosomes w/ centromeres near their ends) fuse at the centromere and the 2 short arms are lost
  • Balanced translocations -> no abnormal phenotype (normally)
  • Unbalanced translocations -> miscarriage, stillbirth, chromosomal imbalance (Down’s, Patau’s, etc.)
62
Q

What are 3 syndromes caused by micro-deletions?

A
  1. Cri-du-chat syndrome
  2. Williams syndrome
  3. 22q11 deletion syndrome
63
Q

What is Cri-du-chat syndrome?

A

Deletion of short arm of chromosome 5

  • Findings: micro-cephaly, moderate -> severe mental retardation, high-pitched crying/mewing, epicanthal folds, cardiac abnormalities
64
Q

What is Williams Syndrome?

A

Deletion of long arm of chromosome 7

  • Findings: distinctive “elfin” facies, mental retardation, hypercalcemia, well-developed verbal skills, extreme friendliness w/ strangers, cardiovascular problems
65
Q

What are 22q11 deletion syndromes?

A
  • DiGeorge syndrome - thymic, parathroid and cardiac defects
  • Velocardiofacial syndrome - palate, facial/cardiac defects
66
Q

Are Y-linked dominant disorders as severe as X-linked dominant disorders?

A

Not as severe b/c Y chromosome only contains a few genes

  • ex: color blindness
67
Q

What is the diff between codominance and incomplete dominance?

A
  • Codominance = both alleles show their effect and DO NOT BLEND (both parents have dominant alleles)
  • Incomplete dominance = both alleles blend their effects

Pathology Exam 1 (5 decks)

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