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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
MARFAN'S SYNDROME MODE of INHERITANCE DEFECT CLINICAL PRESENTATION
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
NEUROFIBROMATOSIS Type 1 (von Recklinghausen's disease) MODE of INHERITANCE DEFECT CLINICAL PRESENTATION
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
NEUROFIBROMATOSIS Type 2 MODE of INHERITANCE DEFECT CLINICAL PRESENTATION
AUTOSOMAL DOMINANT - NF2 gene on Chr 22. [Type 2 = 22] Clinical: - Bilateral ACOUSTIC SCHWANNOMAS - JUVENILE CATARACTS
28
TUBEROUS SCLEROSIS MODE of INHERITANCE CLINICAL PRESENTATION
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
von HIPPEL-LINDAU DISEASE MODE of INHERITANCE DEFECT CLINICAL PRESENTATION
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
CYSTIC FIBROSIS MODE of INHERITANCE DEFECT
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
CYSTIC FIBROSIS DIAGNOSIS & TREATMENT
Diagnosis = PCR of the Chr 7 mutation &/OR ↑↑[Cl⁻] ions in SWEAT TEST Treatment = N-ACETYL-CYSTEINE (cleaves DISULFIDE bond in mucous GLYCOPROTEINS)
32
CYSTIC FIBROSIS CLINICAL PRESENTATION
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
DUCHENNE'S MUSCULAR DYSTROPHY DEFECT Mode of INHERITANCE
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
DUCHENNE'S MUSCULAR DYSTROPHY CLINICAL PRESENTATION & DIAGNOSIS
- PELVIC GIRDLE wkness (progresses SUPERIORLY) - CALF PSEUDO-HYPERTROPHY - CARDIAC myopathy - GOWER'S maneuver use characteristic - ONSET before 5 yo Diagnosis = ⇈CPK & MUSCLE BIOPSY
35
BECKER'S MUSCULAR DYSTROPHY DEFECT Mode of INHERITANCE
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
FRAGILE X SYNDROME Mode of INHERITANCE DEFECT CLINICAL PRESENTATION
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
What are the | ★ TRINUCLEOTIDE EXPANSION DISEASES ★
[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
Which condition has (CAG)x repeats?
(CAG)x repeats = HUNTINGTON'S DZ
39
Which condition has (CTG)x repeats?
(CTG)x repeats = MYO[T]ONIC DYSTROPHY
40
Which condition has (CGG)x repeats?
(CGG)x repeats = FRA[G]ILE X Syndome
41
Which condition has (GAA)x repeats?
(GAA)x repeats = FRIEDRICH'S ATAXIA
42
What is the INCIDENCE of trisomy 21?
Trisomy 21 = DOWN Syndrome 1 : 700
43
What is the INCIDENCE of trisomy 18?
Trisomy 18 = EDWARDS' Syndrome 1 : 8,000
44
What is the INCIDENCE of trisomy 13?
Trisomy 13 = PATAU'S Syndrome 1 : 15,000
45
TRISOMY 21 CLINICAL PRESENTATION
[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
TRISOMY 21 CAUSES
95% = NON-DISJUNCTION of homologous chr (trisomy 21) -- a/w ↑MATERNAL AGE 4% = ROBERTSONIAN TRANSLOCATION 1% = DOWN MOSAICISM -- NO maternal assoc
47
How is Trisomy 21 reflected in the quad screen?
↓ AFP ↓ ESTRIOL ↑ β-hCG ↑ INHIBIN A
48
What is the clinical presentation of trisomy 18?
[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
What is the clinical presentation of trisomy 13?
``` ★ CLEFT LIP / PALATE ★ HOLO-PROSENCEPHALY ★ POLYDACTYLY Micropthalmia Microcephaly ``` Mental retardation - severe Rocker-bottom feet Congenital heart disease DEATH by 1 yo
50
If NONDISJUNCTION of Chr 21 occurs at ANAPHASE I, | what are the chances of OFFSPRING being affected?
100 % ``` 50% = n+1 50% = n-1 ```
51
If NONDISJUNCTION of Chr 21 occurs at ANAPHASE II, | what are the chances of OFFSPRING being affected?
50% ``` 25% = n-1 25% = n+1 ```
52
What is a ROBERTSONIAN TRANSLOCATION?
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
Which Chr are MOST OFTEN involved in ROBERTSONIAN TRANSLOCATIONS?
13, 14, 15 | 21, 22
54
What is a possible result in chromosomal inversions?
↓FERTILITY
55
CRI-DU-CHAT Syndrome DEFECT CLINICAL PRESENTATION
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
WILLIAMS Syndrome DEFECT CLINICAL PRESENTATION
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
22q11 DELETION Syndromes DEFECT CLINICAL PRESENTATION
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
DiGEORGE Syndrome DEFECT CLINICAL PRESENTATION
22q11 deletion. [CATCH-22] THYMIC APLASIA → T-cell deficiency HypO-CALCEMIA 2° to PARATHYROID APLASIA CARDIAC defects
59
VELOCARDIOFACIAL Syndrome DEFECT CLINICAL PRESENTATION
22q11 deletion. CLEFT PALATE ABN FACIES CARDIAC defects

John Step 1 (7 decks)

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