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Biochemistry > Genetics > Flashcards

Genetics Flashcards

0
Q

Variable expressivity

A

Phenotype varies among those with same genotype

- Neurofibromatosis T1 w/ varying severity

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1
Q

Codominance

A

Both alleles contribute to phenotype

- Blood groups A, B, AB (not O); a1-antitrypsin deficiency

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2
Q

Incomplete penetrance

A

Not all those with mutant genotype show mutant phenotype

- BRCA1 gene mutations - not always breast/ovarian ca

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3
Q

Pleiotropy

A

One gene contributes to multiple phenotypic effects

- Untreated PKU - light skin, intellect disability + musty BO

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4
Q

Anticipation

A

Increased severity/earlier onset in each generation

- Huntington’s disease (triNT repeats)

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5
Q

Loss of heterozygosity

A

If pt dx/inherits mutation in tumor suppressor gene, complementary allele must be deleted/mutated before get cancer

  • Not true in oncogenes!
  • Rb with 2-hit-hypothesis
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6
Q

Dominant negative mutation

A

Exerts dominant effect –> heterozygote has nonfxnal gene which prevents nl gene from fxning
- Mutate TF in allosteric site –> can still bind DNA, prevents wild-type TF from binding

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7
Q

Linkage disequilibrium

A

Certain alleles at 2 linked loci to occur more often together than by chance (in population)
- Can vary by population

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8
Q

Mosaicism

A

Genetically distinct line in same individual (mitotic errors after fertilization)

  • Somatic mosaicism = mutation propagates through tissues/organs
  • Gonadal mosaicism = mutation only in egg/sperm cells

McCune Albright synd - lethal if somatic, survivable if mosaic

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9
Q

Locus heterogeneity

A

Mutations at different loci can produce similar phenotype

- Albinism

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10
Q

Allelic heterogeneity

A

Different mutations at same loci produce same phenotype

- B-thalassemia

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11
Q

Heteroplasmy

A

Normal + mutated mtDNA –> variable expression in mitochondrial inherited disease

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12
Q

Uniparental disomy

A

Offspring gets 2 copies of chromosomes from 1 parent, none from other

  • Uniparental is eUploid (correct # chromosomes), not aneuploid
  • Mostly normal phenotype; suspect in someone w/ AR and only 1 parent = carrier
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13
Q

Types of uniparental

A
  • Heterodisomy = heterozygous, meiosis I error

- Isodisomy = homozygous, meiosis II error or postzygotic chrom duplication of 1 pain + loss of other

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14
Q

Hardy-Weinberg

A

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

  • p2 = homo p
  • q2 = homo q
  • 2pq = heterozygosity (carrier in AR)
  • Freq X-linked: males = q; females = q2
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15
Q

Imprinting

A

At some loci, only 1 allele active (other inactive via methylation)

  • If normal allele mutated/deleted = disease
  • i.e. Prader-Willi and Angelman syndrome (chrom 15 genes)
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16
Q

Prader-Willi Syndrome

A

Maternal imprinting - gene from mom is silent, Paternal gene deleted/mutated.

  • Sx - hyperphagia, obesity, intellectual disability, hypogonad, hypotonia
  • 25% maternal uniparental disomy (2 imprinted mom genes; no paternal gene)

“Prader Willi, Paternal gene deleted”

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17
Q

AngelMan syndrome

A

Paternal imprinting - gene from dad silent, Maternal gene deleted/mutated.

  • Sx = inappropriate laughter (happy puppet), sz, ataxia, severe intellectual disab
  • 5% maternal uniparental disomy (2 imprinted paternal genes, no maternal)

“AngelMan, Maternal gene deleted”

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18
Q

Modes of inheritance

A 
Autosomal dominant 
Autosomal recessive
X-linked recessive
X-linked dominant
Mitochondrial inheritance
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19
Q

Autosomal dominant

A

Defects in structural genes

  • Multiple generations, male and female affected (FHx!!)
  • Often pleiotropic
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20
Q

Autosomal recessive

A

Enzyme deficiencies

  • 25% of offspring from 2 carriers affected
  • Often in 1 generation
  • More severe than AD, present in childhood
  • Common in incest families
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21
Q

X-linked recessive

A

Sons of heterozygous mom (carrier) have 50% chance of being affected; more in males

  • No male-to-male (pass through X)
  • Females have to be homozyg to be affected
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22
Q

X-linked dominant

A

Transmitted by both parents

  • Mom - 50% to sons/daughters
  • Dads - 100% to daughters; no sons

i.e. hypophsphatemic rickets (VitD resistant rickets) - wasting of phosphate at proximal tubule –> looks like rickets

23
Q

Mitochondrial inheritance

A

Transmitted through mother only
- All offspring of affected females have disease

  • Mytochondrial myopathies - rare d/o, present with myopathy, lactic acidosis, CNS disease (failure of oxidative phosphorylation)
  • Muscle biopsy = ragged red fibers
24
Q

Autosomal dominant PKD (ADPKD)

A

AD
Adult PKD, bilateral enlargement of kidneys with cysts
- 85% mutated PKD1 (chrom 16)
- 15% mutated PKD2 (chrom 4)

25
Q

Familial adenomatous polyposis

A

AD
Colon covered with adenomatous polyps after puberty
- 100% colon cancer unless resect entire colon
- Mutation APC gene, chrom 5 (5 letters in polyp)

26
Q

Familial hypercholesterolemia

A

AD
High LDL from defective/absent LDL-R
- Severe atherosclerotic disease early in life + tendon xanthomas (Achilles)

27
Q

Hereditary hemorrhagic telangiectasia

A

AD, Osler-Weber-Rendu syndrome
D/o of blood vessels
- Sx: telangiectasias, epistaxis, skin discoloration, AVMs, GI bleeds, hematuria

28
Q

Marfan syndrome

A

AD, connective tissue d/o affecting skeleton, heart, eyes

  • Fibrillin-1 gene mutation
  • Tall, long extremities, pectus excavatum, hypermobile joints, long/tapering fingers/toes
  • Cystic medial necrosis of aorta = dissecting AA; floppy mitral valve
  • Lenses subluxed (up/temporally)
29
Q

Huntington disease

A

AD

  • Depression, progressive dementia, choreiform mvmnt, caudate atrophy, decr level GABA/ACh in brain
  • Gene on Chrom 4 –> trinucleotide repeats CAG (more repeats = younger onset)
  • “Hunting 4 food”
  • “CAG - caudate loss of ACh and GABA”
30
Q

Multiple endocrine neoplasias

A

AD, familial tumors of endocrine glands –> MEN 1, 2a, 2b

  • MEN 1 = 3Ps: parathyroid, pancreas, pituitary
  • MEN2a = medullary ca of thyroid, pheo, parathyroid hyperplasia
  • MEN2b = medullary ca of thyroid, pheo, mucosal neuromas
  • 2a/2b assoc w/ RET gene mut
31
Q

Neurofibromatosis (NF) type 1

A

AD, 100% penetrance, variable expression

  • Neurocutaneous d/o with cafe-au-lait spots + cutaneous neurofibromas
  • NF1 gene, Chrom 17
32
Q

Neurofibromatosis type 2

A

AD

  • Bilateral acoustic schwannomas, juvenile cataracts, meningiomas, emendymomas
  • NF2 gene, chrom 22 (type 2=22)
33
Q

Tuberous sclerosis

A

AD, incomplete penetrance, variable expression

  • Neurocutaneous disease affecting many organs
  • Benign hamartomas
34
Q

von Hippel-Lindau disease

A

AD
- Dx tumors (benign + malig),
- Deletion of VHL gene (tumor suppressor) on chrom 3
[VHL = 3 works for chrom 3]

35
Q

Autosomal recessive diseases

A 
Albinism
ARPKD (infantile PKD), CF, glycogen storage disease, hemochromatosis, Kartagener syndrome, mucopolysaccharidosis, PKU, sickle cell, thalassemias, Wilson disease
36
Q

CF presentation

A

Dx - incr Cl- sweat concentration OR more negative transepithelial potential difference

  • Get contraction alkalosis + hypokalemia (Na/H2O loss, kidney K+/H+ wasting)
  • Recurrent pulm infections (Pseudomonas), pancreatic insuffic/malabs/steatorrhea (fat-soluble vit defic), meconium ileus in newborn
  • Infertility in males, absent vas/sperm

Tx = N-acetylcysteine to loosen mucus, DNAase to clear debris

37
Q

Cystic fibrosis genetics

A

AR, defect in CFTR on chrom 7 (del Phe508)

  • CFTR - encodes **ATP-gated Cl- channel –> secretes Cl- into lungs and GI tract; absorbs Cl- in sweat glands
  • Cl- creates gradient, lets Na+/H2O follow*

Mutation: misfolded protein, stays in RER and not to cell membrane

  • Decr Cl- secretion (high intracellular Cl-); then Na+ and H20 are reabsorped to compensate = thick mucus in lungs/GI
  • Get
  • Get high Cl- sweat test bc CFTR gene allows reabs of Cl- in sweat glands
38
Q

X-linked recessive disorders

A

“Be Wise, Fool’s GOLD Heeds Silly HOpe”

  • Bruton agammaglobulinemia, Wiskott-Aldrich, Fabry disease, G6PD defic, Ocular albinism, Lesch-Nyhan, Duchenne (and Becker) muscular dystrophy, Hunter Syndrome, Hemophilia A/B, Ornithine transcarbamylase deficiency
39
Q

Muscular dystrophies

A

Duchenne - X-linked frameshift mutation in dystrophin
Becker - X-linked point mutation in dystrophin
Myotonic type 1 - CTG trinucl expansion (DMPK gene)

  • Western blot/muscle biopsy to confirm
40
Q

Dystrophin

A

Helps anchor muscle fibers (skeletal/cardiac)

  • DMD gene = longest coding region of any human gene, so higher chance of mutation
  • Connects actin extracellular matrix (ECM)
  • Higher CPK and aldolase (from muscle breakdown)
41
Q

Duchenne muscular dystrophy

A

X-linked framshift mutation in dystrophin –> get accel muscle breakdown; onset age 5
“Duchenne = deleted dystrophin”
- Weakness in pelvic girdle –> moves up
- Sx: Pseudohypertrophy of calf m (fibrofatty replacement of muscle)
- Gower manuever - pts use upper extremity to help stand
- Die from dilated cardiomyopathy

42
Q

Becker muscular dystrophy

A

X-linked point mutation in dystrophin gene (not framshift)

- Less severe, onset adolescence/early childhood

43
Q

Myotonic type 1

A

CTG trinucleotide repeat expansion of DMPK gene
- Abnormal myotonin protein kinase expressed –> myotonia, muscle wasting, frontal balding, cataracts, testicular atrophy, arrhythmia

44
Q

Fragile X syndrome

A

X-linked defect –> FMR1 gene methylated; CGG trinucleotide repeat d/o
- 2nd most common intellectual disability (after Down’s)
- Sx: macroorchidism (large balls), long face, large everted ears, autism, MVprolapse
“Fragile X has eXtra large testes”

45
Q

Trinucleotide repeat expansion diseases

A

“Try (trinucleotide) hunting for my fried eggs (X)”

Huntington disease, Friedreich ataxia, myotonic dystrophy, fragile X syndrome

X-Girlfriends First Aid Helped Ace My Test

  • Fragile X = CGG
  • Friedreich ataxia = GAA
  • Huntington disease = CAG
  • Myotonic disease = CTG
46
Q

Autosomal trisomies

A
  • Down syndrome (Trisomy 21); drink at age 21
  • Edwards syndrome (Trisomy 18); elections at age 18
  • Patau syndrome (Trisomy 13); puberty at age 13
47
Q

Down syndrome

1:700

A

Trisomy 21, most common chromosomal d/o, most common cause of intellectual disability

  • Intellectual disability, flat facies, epicanthal folds, gap btwn toes, duodenal atresia, Hirschsprung disease, congenital heart defects, Brushfield spots on iris
  • Assoc: AML/ALL, early alzheimer’s (>35yo)

95% nonhomologous meiotic nondisjxn of homologous chromosomes; 4% robertsonian translocation; 1% mosaicism (mitotic error post-fertiliz)

(PAPP-A down, nuchal/BhCG up; Quad: AFP down, others up)

48
Q

Edwards syndrome

1:8,000

A

Trisomy 18
- Severe intellect disability, rocker-bottom feet, micrognathia, low-set Ears, clenched hands, prominent occiput
- Death w/in 1 yr
(PAPPA-A/BhCG down; Quad screen: all 4 down)

49
Q

Patau syndrome

1:15,000

A

Trisomy 13
- Severe intellect disability, rocker-bottom feet, micropthalmia/microcephaly, cleft liP/Palate, holoProsencephaly, Polydactyly
- Death w/in 1 yr
(PAPP-A/BhCG down, nuchal up)

50
Q

Robertsonian translocation

A

2 long arms fuse at centromere, and 2 short arms lost

  • Balanced = no problems
  • Unbalanced = miscarriage, stillbirth, chrom imbalance (Down’s, Patau’s)
51
Q

Meiotic nondisjunction

A

Chromosomes don’t separate either in meiosis 1 or meiosis 2

52
Q

Cri-du-chat syndrome

A

Congenital microdeletion of short arm of Chrom 5 (46XX or XY, 5p-)
- Microcephaly, intellectual disability, high-pitched crying/mewing, epicanthal folds, cardiac abnormalities (VSD)

“Cri du chat = cry of the cat”

53
Q

Williams syndrome

A

Congenital deletion of long arm chrom 7 (w/ elastin gene)
- “Elfin” facies, intellectual disability, hypercalcemia (incr sensitivity to VitD), well-dx verbal skills, extreme friendliness w/ strangers, CV problems

54
Q

22q11 deletion

A

CATCH 22

  • Cleft palate, abnormal facies, thymic aplasia –> T-cell defic, cardiac defects, hypocalcemia 2/2 to PTH hypoplasia
  • Microdeletion in chrom 22q11
  • *Aberrant dx of branchial pouch 3 and 4
55
Q

DiGeorge syndrome

A

Variant of 22q11 deletion

  • Thymic, parathyroid, cardiac defects
  • Aberrant dxment of 3rd/4th branchial pouches
56
Q

Velocardiofacial syndrome

A

Variant of 22q11 deletion

  • Palate, facial, cardiac defects
  • Aberrant dxment of 3rd/4th branchial pouches

Biochemistry (6 decks)

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