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USMLE Step 1 Systems > Genetics > Flashcards

Genetics Flashcards

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USMLE® Step 1 flashcards
1
Q

Sx of Fragile X. What gene mutated and how does it cause disease?

A
  1. MR
  2. Macroorchidism*
  3. Facial: long face, big jaw, big ears, cleft palate
  4. Joint: laxity, short height, pes cavus, etc
  5. MVP

FMR1 (fragile x mental retardation gene 1) - CGG repeats. Leads to gene hypermethylation and gene inactivation. Gene is impt for normal neural development.

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2
Q

Trisomy 21 increases risk of what malignancies?

A

Acute lymphoblastic leukemia
Acute myelogenous leukemia

Look for auer rods in myelogenous.

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3
Q

Cystic Fibrosis - what is lost in sweat?

A

Sodium and Chloride.

Free water is NOT lost with sweating bc its not hypotonic like normal. When first made, eccrine sweat is isotonic and as it travel thru duct, chloride is resorbed thru CFTR and sodium follows resulting in hypotonic sweat.

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4
Q

Wiskott Aldrich Manifestations

A
  1. eczema
  2. recurrent infection
  3. thrombocytopenia

Combined B and T lymphocyte disorder due to mutation on X chromosome.

Tx: Bone Marrow Transplant

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5
Q

3 Causes of Down’s Syndrome

A
  1. Trisomy 21 - nondisjunction
  2. Unbalanced Robersonian translocation - extra arm of 21 attached to another chr
  3. mosaicism - one cell line with nl genotype; another with trisomy 21
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6
Q

Pleiotropy

A

Multiple phenotypic manifestations resulting from a single gene mutation.

Most syndromic disorders are pleiotropic.

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7
Q

Digeorge is caused by maldevelopment of what?

A

3rd and 4th pharyngeal pouches.

deletion of chr 22 - T cell immunodeficiency

  • absence of thymic shadow
  • hypoCa tetany (no parathyroid)
  • cleft palate
  • mandibular deformity
  • low set ears
  • aortic arch abnormalities
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8
Q

Male Pattern Baldness (Androgenic Alopecia) - inherited how?

A

Polygenic inheritance with variable penetrance.

Depends on circulating androgen levels and degree of genetic predisposition.

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9
Q

What is mitochondrial inheritance?

A

Exclusively-maternal inheritance: affects both male and female offspring with equal frequency (100%), but variable severity due to heteroplasmy (random distribution of nl and abnl mitochondria during mitosis).

Ex:

  • Leber hereditary optic neuropathy: bilateral vision loss
  • Myoclonic epilepsy with ragged red fibers
  • MELAS: mito encephalopathy with lactic acidosis and stroke like episodes.
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10
Q

How does Turner’s result in 45XO?

A

Mitotic error during early development.

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11
Q

Li Fraumeni - inheritance and manifestations?

A

AD - mutation in p53

Early-onset cancers: breast cancer, bone and soft tissue sarcomas, adrenocortical carcinoma, brain tumors.

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12
Q

HNPCC - Adenomatous Polyposis

A

AD - MSH2 or ML (tumor suppressor)

Colorectal or Endometrial Cancer

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13
Q

Familial Adenomatous Polyposis

A

AD - APC (tumor suppressor)

Colon
Osteoma
Brain Tumors

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14
Q

Von Hippel Lindau

A

AD - VHL (tumor suppressor)

Hemangioblastoma
Clear cell renal carcinoma
Pheochromocytoma

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15
Q

MEN I vs. MEN II Inheritance

A

MEN I: MEN I gene - AD - tumor suppressor gene

MEN II: RET- AD - proto-oncogene

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16
Q

Inheritance of Duchenne and Becker Muscular Dystrophy

A

Duchenne: X-linked frameshift -> deleted dystrophin
Muscular: X-linked point mutation

17
Q

Genetic Heterogeneity

A

Mutations of different genes cause similar phenotypes

18
Q

Allelic Heterogeneity

A

Different mutations in the same gene locus cause similar phenotypes

19
Q

Phenotypic Heterogeneity

A

Mutations of the same gene cause different phenotypes

20
Q

Polyploidy

A

More than two sets of homologous chromosomes.

Like 3n

21
Q

Pleiotrophy

A

Single genetic defect -> Multiple simultaneous phenotypic effects

22
Q

Expressivity

A

Variation in phenotypic severity among individuals with the same genetic mutation.

23
Q

Cause of Prader Willi vs. AngelMan’s

A

Prader Willi:

  • Paternal gene deleted; Maternal inactivated
  • Both 15s inherited from mom

AngelMan

  • Maternal gene deleted; Paternal inactivated
  • Both 15s from paternall.
24
Q

Hox Genes

A

Guide morphogenesis, esp segmental organization.
Mutation causes structural defects

Ex: HoxA13 - hand, foot, genital syndrome

25
Q

What genetic disease associated with cystic hygromas?

A

Turner’s

26
Q

BRAF mutation V600E

A

Melanoma

27
Q

Peutz-Jegher’s

A

Autosomal Dominant
- mutation in serine/threonine kinase (chr 19)

  1. Pigmented Mucocutaneous Macules - lips, buccal mucosa*, hands, feet
  2. Multiple Hamartomatous polyps - usually benign, excessive growth can cause sx.

Increased risk of CRC and other visceral malignancies.

USMLE Step 1 Systems (11 decks)

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