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John Step 1 > Genetics > Flashcards

Genetics Flashcards

1
Q

HARDY-WEINBERG EQUILIBRIUM

ASSUMES?

A

① No MUTATION at locus
② No SELECTION for mutant locus
③ No MIGRATION
④ RANDOM mating (completely)

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2
Q

If in HARDY-WEINBERG EQUILIBRIUM

DISEASE PREVALENCE

A

p² + 2pq + q² = 1

p & q are separate alleles

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3
Q

If in HARDY-WEINBERG EQUILIBRIUM

ALLELE PREVALENCE

A

p + q = 1

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4
Q

If in HARDY-WEINBERG EQUILIBRIUM

HETEROZYGOTE PREVALENCE

A

2pq

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5
Q

If in HARDY-WEINBERG EQUILIBRIUM

PREVALENCE of X-LINKED RECESSIVE DISEASE

A

q in ♂

q² in ♀

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6
Q

IMPRINTING

DEFECT
SYNDROMES

A

At a single locus, only 1 allele is ACTIVE

  • the other is INACTIVE = IMPRINTED / INACTIVATED by methylation.
  • DELETION of ACTIVE ALLELE → DISEASE

IMPRINTING Syndromes - d/t inactivation / deletion of genes on chr 15
or UNIPARENTAL DISOMY:

(1. ) PRADER-WILLI
(2. ) ANGELMAN’S

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7
Q

PRADER-WILLI Syndrome

DEFECT
CLINICAL PRESENTATION

A

DELETION of normally active PATERNAL allele on Chr 15 (or uniparental disomy)
& Imprinted maternal genes

Clinical:

  • Mental retardation
  • AGGRESSIVE behaviour
  • HypO-TONIA
  • HypO-GONADISM
  • HypER-PHAGIA + OBESITY
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8
Q

ANGELMAN’S Syndrome

DEFECT
CLINICAL PRESENTATION

A

DELETION of normally active MATERNAL allele on Chr 15 (or uniparental disomy)
& Imprinted paternal genes

Clinical: “HAPPY PUPPET”

  • Mental retardation
  • SEIZURES
  • ATAXIA
  • INAPPROPRIATE LAUGHTER
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9
Q

MODES of INHERITANCE

AUTOSOMAL DOMINANT

A
  • Many generations, both sexes, affected
  • FHx crucial to Dx

Often

  • PLEIOTROPIC
  • d/t defects in STRUCTURAL GENES
  • Present AFTER PUBERTY
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10
Q

MODES of INHERITANCE

AUTOSOMAL RECESSIVE

A
  • 25% of offspring from 2 CARRIER parents affected
  • seen in only 1 generation

Often

  • d/t ENZYME DEFICIENCIES
  • more SEVERE vs dominant disorders
  • Present in CHILDHOOD
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11
Q

★ AUTOSOMAL RECESSIVE DISEASES ★

A

[MATCH the GAPSS]

MUCOPOLYSACCHARIDOSES (except Hunter's)
ARPKD
THALASSEMIAS
CYSTIC FIBROSIS
HEMOCHROMATOSIS
GLYCOGEN STORAGE Dzs
ALBINISM
PHENYLKETONURIA
SICKLE CELL ANAEMIAS
SPHINGOLIPIDOSES (except Fabry's)
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12
Q

MODES of INHERITANCE

X-LINKED RECESSIVE

A
  • 50% of SONS from HETEROz MOTHERS
  • NO ♂-to-♂ transmission
  • Often more SEVERE in ♂
  • HETEROz ♀ rarely affected d/t RANDOM INACTIVATION of an X Chr in each cell
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13
Q

★ X-LINKED RECESSIVE DISORDERS ★

A

[Be Wise, Fools GOLD Heeds silly Hope]

BRUTONS AGAMMAGLOBULINEMIA
WISKOTT-ALDRICH Syndrome
FABRY'S Dz
G6PD Deficiency
OCULAR ALBINISM
LESCH-NYHAN Syndrome
DUCHENNE'S / BECKER'S
HUNTER'S Syndrome
HAEMOPHILIA A/B
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14
Q

MODES of INHERITANCE

X-LINKED DOMINANT

A
  • Transmitted thru BOTH PARENTS
  • ♂/♀ offspring from affected MOTHER may be affected
  • ALL ♀ offspring of affected FATHER are diseased

Eg. HYPO-PHOSPHATEMIC RICKETS = Inherited d/o
→ ↑ PO₄ WASTING at PROXIMAL TUBULE
→ RICKETS-like presentation

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15
Q

MODES of INHERITANCE

MITOCHONDRIAL INHERITANCE

A
  • Transmitted ONLY thru MOTHER
  • ALL offspring of affected mother may show signs of dz
  • Variable expression in population d/t HETEROPLASMY

Eg. Mitochondrial Inheritance Diseases:
① Mitochondrial myopathies
② Leber’s Hereditary Optic Neuropathy

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16
Q

LEBER’S HEREDITARY OPTIC NEUROPATHY

MODE of INHERITANCE
PATHOGENESIS

A

MITOCHONDRIAL INHERITANCE

  • Degeneration of RETINAL GANGLION cells + AXONS
    → ACUTE CENTRAL VISION LOSS
    & WPW Syndrome
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17
Q

ACHONDROPLASIA

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT

CELL-SIGNALLING defect of FGFr3
(fibroblast growth factor receptor 3).

Clinical:

  • DWARFISM (short limbs)
  • normal head & trunk size
  • a/w PATERNAL AGE
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18
Q

ADPKD

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DZ

  • 90% d/t defective APKD1 Chr 16
    [16 letters in “polycystic kidney”]

Clinical:

  • BILATERAL kidney enlargement d/t multiple large cysts
  • FLANK PAIN
  • HTN
  • HEMATURIA
  • RENAL FAILURE
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19
Q

ADPKD

ASSOCIATED CONDITIONS

A

AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DZ

Associated w/:

  • BERRY ANEURYSMS
  • MITRAL VALVE PROLAPSE
  • POLYCYSTIC LIVER DZ
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20
Q

FAMILIAL ADENOMATOUS POLYPOSIS
(FAP)

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT

Chr 5 deletion of APC gene → → Error in DNA repair.
[5 letters in “polyp”]

Clinical:
- Adenomatous polyps cover colon after puberty
→ COLON Ca unless resected.

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21
Q

FAMILIAL HYPERCHOLESTEROLEMIA

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

Absent / ⇊ LDL RECEPTORS (AD)
→ → ⇈LDL

Clinical:
“Hypercholesterolemia” - elevated bld cholesterol
⁂ Heteroz: chol ~300 mg/dL
⁂ HOMOz: chol ~700.
– ACRUC - corneal
– Achilles / eyelid XANTHOMAS
– Accelerated ATHEROSCLEROSIS, AMI early

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22
Q

HEREDITARY HEMORRHAGIC TELANGECTASIA
(OSLER-WEBER-RENDU Syndrome)

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT

  • Disorder of BLOOD VESSELS.

Clinical: [STAR]

  • Skin discolouration
  • TELANGIECTASIA
  • AVMs
  • Recurrent EPISTAXIS
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23
Q

HEREDITARY SPHEROCYTOSIS

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT

  • SPECTRIN / ANKRIN defect → → SPHEROID RBCs

Clinical:

  • HAEMOLYTIC ANAEMIA
  • ↑MCHC
  • SPLENECTOMY = curative
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24
Q

HUNTINGTON’S DISEASE

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT

  • Chr 4 (CAG)x trinucleotide repeat disorder
    → ↓GABA & ↓ACh in brain
    → CAUDATE ATROPHY

Clinical:

  • Onset 20 - 50 yo
  • CHORIEFORM movement
  • DEPRESSION
  • Progressive DEMENTIA
25
Q

MARFAN’S SYNDROME

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT
- FIBRILLIN gene mutation.

Clinical: (+ pectus EXCAVATUM)
[MARFAN’S]
– MITRAL VALVE Prolapse
– Ao Incompetence + ANEURYSMS d/t cystic medial Ao necrosis
– Retinal detachment
– FIBRILLIN gene mutation
– ARACHNODACTYLY (= tapering fingers + toes)
– Neg Nitroprusside test (vs homocystinuria)
– SUBLUX LENS

26
Q

NEUROFIBROMATOSIS Type 1
(von Recklinghausen’s disease)

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT

  • LONG ARM of Chr 17

Clinical:

  • CAFE-AU-LAIT spots
  • LISCH nodules (pigmented iris hamartomas)
  • OPTIC pathway GLIOMAS
  • NEURAL TUMOURS
  • SCOLIOSIS (skeletal d/o)
27
Q

NEUROFIBROMATOSIS Type 2

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT

  • NF2 gene on Chr 22.
    [Type 2 = 22]

Clinical:

  • Bilateral ACOUSTIC SCHWANNOMAS
  • JUVENILE CATARACTS
28
Q

TUBEROUS SCLEROSIS

MODE of INHERITANCE
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT

  • INCOMPLETE penetrance
  • VARIABLE presentation

Clinical:

  • ADENOMA SEBACEUM (facial lesions)
  • ‘ASH LEAF SPOTS’ (hypopigmented skin)
  • Renal ANGIOMYOLIPOMAS + CYSTS
  • ↑ASTROCYTOMAS incidence
  • CORTICAL + RETINAL HAMARTOMAS
  • Cardiac RHABDOMYOMAS (= hamartoma)
  • SEIZURES
29
Q

von HIPPEL-LINDAU DISEASE

MODE of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

AUTOSOMAL DOMINANT

  • Deletion of VHL gene on Chr 3 (= tumour suppressor)
    → constitutive expression of HIF (= TF) &
    → ANGIOGENIC GF activation.

Clinical:

  • HEMANGIOBLASTOMA of RETINA / CEREBELLUM / MEDULLA
  • BILATERAL RCC (50%)
30
Q

CYSTIC FIBROSIS

MODE of INHERITANCE
DEFECT

A

AUTOSOMAL RECESSIVE
⁂ Most common lethal genetic dz in Caucasians

CFTR channel actively

  • SECRETES Cl⁻ in LUNGS + GIT
  • REABSORBS Cl⁻ from SWEAT

DEFECT:
- Deletion of Phe at position 508 in CFTR gene on Chr 7.
→ Abn PROTEIN FOLDING
→ CFTR Cl⁻ channel DEGRADED ā reaching plasma membrane
→ Defective Cl⁻ channel → secrete abnormally THICK MUCUS

31
Q

CYSTIC FIBROSIS

DIAGNOSIS
&
TREATMENT

A

Diagnosis =
PCR of the Chr 7 mutation
&/OR
↑↑[Cl⁻] ions in SWEAT TEST

Treatment = N-ACETYL-CYSTEINE
(cleaves DISULFIDE bond in mucous GLYCOPROTEINS)

32
Q

CYSTIC FIBROSIS

CLINICAL PRESENTATION

A

① Recurrent PULMONARY infx (S. aureus, Pseudomonas)
→ Chronic BRONCHITIS & BRONCHIECTASIS

② PANCREATIC INSUFFICIENCY
→ (MALABSORPTION + STEATORRHEA)
→ Fat soluble VIT (A,D,E,K) deficiency

③ ♂ INFERTILITY
– d/t BILATERAL absence of VAS DEFERENS

④ MECONIUM ILEUS (newborns)

33
Q

DUCHENNE’S MUSCULAR DYSTROPHY

DEFECT
Mode of INHERITANCE

A

DYSTROPHIN helps ANCHOR SKELETAL + CARDIAC mm fibers

DEFECT: (X-linked RECESSIVE)
X-linked FRAME SHIFT mutation
→ DYSTROPHIN (DMD) gene DELETION
→ ACCELERATED MM BREAKDOWN

DYSTROPHIN gene = LONGEST known human gene
→ ⇈susceptible to mutation

34
Q

DUCHENNE’S MUSCULAR DYSTROPHY

CLINICAL PRESENTATION
&
DIAGNOSIS

A
  • PELVIC GIRDLE wkness (progresses SUPERIORLY)
  • CALF PSEUDO-HYPERTROPHY
  • CARDIAC myopathy
  • GOWER’S maneuver use characteristic
  • ONSET before 5 yo

Diagnosis = ⇈CPK & MUSCLE BIOPSY

35
Q

BECKER’S MUSCULAR DYSTROPHY

DEFECT
Mode of INHERITANCE

A

DEFECT: (X-linked RECESSIVE)
X-linked DYSTROPHIN (DMD) gene MUTATION
- less severe than not having gene at all (= Duchenne’s)

  • ONSET = ADOLESCENCE / EARLY ADULT
36
Q

FRAGILE X SYNDROME

Mode of INHERITANCE
DEFECT
CLINICAL PRESENTATION

A

X-linked RECESSIVE defect affecting
FMR1 gene METHYLATION
- a/w Chr breakage
- (CGG)x repeats

Clinical: [MALE]

  • MACRO-ORCHIDISM
  • MITRAL PROLAPSE
  • AUTISM
  • LONG FACE, LARGE JAW
  • EVERTED EARS
37
Q

What are the

★ TRINUCLEOTIDE EXPANSION DISEASES ★

A

[Hunting for My Fried X]

HUNTINGton’s dz = (CAG)x

MYo[t]onic dystrophy = (CTG)x

FRIEDrich’s [a]taxi[a] = (GAA)x

fra[g]ile X syndrome = (CGG)x

38
Q

Which condition has (CAG)x repeats?

A

(CAG)x repeats = HUNTINGTON’S DZ

39
Q

Which condition has (CTG)x repeats?

A

(CTG)x repeats = MYO[T]ONIC DYSTROPHY

40
Q

Which condition has (CGG)x repeats?

A

(CGG)x repeats = FRA[G]ILE X Syndome

41
Q

Which condition has (GAA)x repeats?

A

(GAA)x repeats = FRIEDRICH’S ATAXIA

42
Q

What is the INCIDENCE of trisomy 21?

A

Trisomy 21 = DOWN Syndrome

1 : 700

43
Q

What is the INCIDENCE of trisomy 18?

A

Trisomy 18 = EDWARDS’ Syndrome

1 : 8,000

44
Q

What is the INCIDENCE of trisomy 13?

A

Trisomy 13 = PATAU’S Syndrome

1 : 15,000

45
Q

TRISOMY 21

CLINICAL PRESENTATION

A

[DEAD FACTS]

Dumb - Mental retardation
EPICANTHAL FOLDS
ALZHEIMER’S Dz - early
DUODENAL ATRESIA

FLAT facies
ALL - ↑ risk (acute lymphoblastic leukemia)
Congenital heart dz (usu SEPTUM PRIMUM-type ASD)
TOE GAP 1st-2nd
SIMIAN CREASE

46
Q

TRISOMY 21

CAUSES

A

95% = NON-DISJUNCTION of homologous chr (trisomy 21)
– a/w ↑MATERNAL AGE

4% = ROBERTSONIAN TRANSLOCATION

1% = DOWN MOSAICISM
– NO maternal assoc

47
Q

How is Trisomy 21 reflected in the quad screen?

A

↓ AFP
↓ ESTRIOL

↑ β-hCG
↑ INHIBIN A

48
Q

What is the clinical presentation of trisomy 18?

A

[EDWARDS’]

Eighteen = trisomy 18
Digit overlapping flexion = ★ CLENCHED HANDS
Wide head = prominent occiput
Absent intellect - severe MR
Rocker-bottom feet
Diseased heart = Congenital heart dz
Small jaw = ★ MICROGNATHIA

DEATH by 1 yo

49
Q

What is the clinical presentation of trisomy 13?

A 
★ CLEFT LIP / PALATE
★ HOLO-PROSENCEPHALY
★ POLYDACTYLY
Micropthalmia
Microcephaly

Mental retardation - severe
Rocker-bottom feet
Congenital heart disease

DEATH by 1 yo

50
Q

If NONDISJUNCTION of Chr 21 occurs at ANAPHASE I,

what are the chances of OFFSPRING being affected?

A

100 %

50% = n+1
50% = n-1
51
Q

If NONDISJUNCTION of Chr 21 occurs at ANAPHASE II,

what are the chances of OFFSPRING being affected?

A

50%

25% = n-1
25% = n+1
52
Q

What is a ROBERTSONIAN TRANSLOCATION?

A

LONG ARMS of 2 ACROCENTRIC Chr FUSE at the CENTROMERE
→ SHORT ARMS are lost
(= NON-RECIPROCAL Chr translocation)

ACROCENTRIC Chr = Chr w/ centromeres near their ends

  • BALANCED translocations → normal phenotype
  • UNBALANCED translocations → miscarriage, stillbirth, Trisomy syndromes
53
Q

Which Chr are MOST OFTEN involved in ROBERTSONIAN TRANSLOCATIONS?

A

13, 14, 15

21, 22

54
Q

What is a possible result in chromosomal inversions?

A

↓FERTILITY

55
Q

CRI-DU-CHAT Syndrome

DEFECT
CLINICAL PRESENTATION

A

Congenital microdeletion of SHORT ARM of chr 5
(46,XX or XY,5p–)

CLINICAL:
HIGH PITCHED CRYING / mewing (“cry of the cat”)
EPICANTHAL folds
MICROCEPHALY

Mental retard-mod-severe
Cardiac abnormalities

56
Q

WILLIAMS Syndrome

DEFECT
CLINICAL PRESENTATION

A

Microdeletion of LONG ARM of chr 7
(includes ELASTIN gene)

CLINICAL: [CDEFGH]
Cardiac abnormalities
Dumb - mental retardation
"ELFIN" facies
FRIENDLY - extremely
GLIB - well developed VERBAL SKILLS
HYPERCALCEMIA d/t ↑ Vit D sensitivity
57
Q

22q11 DELETION Syndromes

DEFECT
CLINICAL PRESENTATION

A

Microdeletion at Chr 22q11 →
ABN development of 3rd + 4th BRACHIAL POUCHES

CLINICAL: [CATCH-22]
CLEFT PALATE
ABN FACIES
THYMIC APLASIA → T-cell deficiency
CARDIAC defects
HypO-CALCEMIA 2° to PARATHYROID APLASIA
58
Q

DiGEORGE Syndrome

DEFECT
CLINICAL PRESENTATION

A

22q11 deletion.
[CATCH-22]

THYMIC APLASIA → T-cell deficiency
HypO-CALCEMIA 2° to PARATHYROID APLASIA
CARDIAC defects

59
Q

VELOCARDIOFACIAL Syndrome

DEFECT
CLINICAL PRESENTATION

A

22q11 deletion.

CLEFT PALATE
ABN FACIES
CARDIAC defects

John Step 1 (7 decks)

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