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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
Autosomal dominant PKD (ADPKD)
AD Adult PKD, bilateral enlargement of kidneys with cysts - 85% mutated PKD1 (chrom 16) - 15% mutated PKD2 (chrom 4)
25
Familial adenomatous polyposis
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
Familial hypercholesterolemia
AD High LDL from defective/absent LDL-R - Severe atherosclerotic disease early in life + tendon xanthomas (Achilles)
27
Hereditary hemorrhagic telangiectasia
AD, Osler-Weber-Rendu syndrome D/o of blood vessels - Sx: telangiectasias, epistaxis, skin discoloration, AVMs, GI bleeds, hematuria
28
Marfan syndrome
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
Huntington disease
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
Multiple endocrine neoplasias
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
Neurofibromatosis (NF) type 1
AD, 100% penetrance, variable expression - Neurocutaneous d/o with cafe-au-lait spots + cutaneous neurofibromas - NF1 gene, Chrom 17
32
Neurofibromatosis type 2
AD - Bilateral acoustic schwannomas, juvenile cataracts, meningiomas, emendymomas - NF2 gene, chrom 22 (type 2=22)
33
Tuberous sclerosis
AD, incomplete penetrance, variable expression - Neurocutaneous disease affecting many organs - Benign hamartomas
34
von Hippel-Lindau disease
AD - Dx tumors (benign + malig), - Deletion of VHL gene (tumor suppressor) on chrom 3 [VHL = 3 works for chrom 3]
35
Autosomal recessive diseases
``` Albinism ARPKD (infantile PKD), CF, glycogen storage disease, hemochromatosis, Kartagener syndrome, mucopolysaccharidosis, PKU, sickle cell, thalassemias, Wilson disease ```
36
CF presentation
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
Cystic fibrosis genetics
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
X-linked recessive disorders
"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
Muscular dystrophies
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
Dystrophin
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
Duchenne muscular dystrophy
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
Becker muscular dystrophy
X-linked point mutation in dystrophin gene (not framshift) | - Less severe, onset adolescence/early childhood
43
Myotonic type 1
CTG trinucleotide repeat expansion of DMPK gene - Abnormal myotonin protein kinase expressed --> myotonia, muscle wasting, frontal balding, cataracts, testicular atrophy, arrhythmia
44
Fragile X syndrome
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
Trinucleotide repeat expansion diseases
"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
Autosomal trisomies
- 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
Down syndrome | 1:700
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
Edwards syndrome | 1:8,000
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
Patau syndrome | 1:15,000
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
Robertsonian translocation
2 long arms fuse at centromere, and 2 short arms lost - Balanced = no problems - Unbalanced = miscarriage, stillbirth, chrom imbalance (Down's, Patau's)
51
Meiotic nondisjunction
Chromosomes don't separate either in meiosis 1 or meiosis 2
52
Cri-du-chat syndrome
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
Williams syndrome
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
22q11 deletion
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
DiGeorge syndrome
Variant of 22q11 deletion - Thymic, parathyroid, cardiac defects - Aberrant dxment of 3rd/4th branchial pouches
56
Velocardiofacial syndrome
Variant of 22q11 deletion - Palate, facial, cardiac defects - Aberrant dxment of 3rd/4th branchial pouches

Biochemistry (6 decks)

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