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Week 1 - Medical Genetics > Atypical Mandelian Inheritance > Flashcards

Atypical Mandelian Inheritance Flashcards

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1
Q

What are the atypical mandelian inheritance?

A
  1. Genetic anticipation
  2. Pseudoautosomal inheritance
  3. Pseudodominant inheritance
  4. Mitochondrial inheritance
  5. Mosaicism
  6. Imprinting disorders
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2
Q

Define Genetic Anticipation

A

Tendency in certain genetic disorders for individuals in successive generations to present at an earlier age and / or with more severe manifestations

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3
Q

What is the common mechanism of Genetic Anticipation?

A

Expression of a trinucleotide repeat mutation.

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4
Q

Examples of disorder with Genetic Anticipation.

A
  1. Huntington’s disease
  2. Mytonic dystrophy
  3. Fragile X syndrome
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5
Q

Pathogenesis of Huntington’s disease?

A

Upstream (towards 5’ end of DNA) CAG repeats in Huntingtin Protein Gene in Chromosome 4 – CAG triplets increase – formation of polyGLUTAMINE chain – aggregation of polyglutamine chains – cell death in caudate and putamen

AUTOSOMAL DOMINANT INHERITANCE

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6
Q

Pathogenesis of Myotonic dystrophy

A

Downstream (Towards 3’ end of DNA) repeats of CTG – affect splicing of RNA

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7
Q

What is Pseudoautosomal Inheritance?

A

Close homology between X & Y chromosomes in the pseudoautosomal region (PAR) at the short arm tip of X Chromosome

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8
Q

Features of Pseudoautosomal Inheritance?

A
  1. Pseudoautosomal regions are not affected by X-inactivation
  2. Xpar and Ypar have genetic recombination
  3. There is Male to Male transmission
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9
Q

Example of Pseudoautosomal Inheritance?

A

Madelung’s deformity

  • defective SHOX gene : Short stature HOmeoboX gene

growth disturbance in epiphyseal growth plate of distal radius – radius grows but curves towards palm – Ulna is pushed medially – prominent distal ulna

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10
Q

What is pseudodominant inheritance?

A

Autosomal recessive genes that behave like Autosomal Dominance due to increased carrier frequency.

  • too many carriers
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11
Q

Example of Pseudodominant inheritance?

A

Gilbert syndrome

- intermittent unconjugated hyperbilirubinaemia

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12
Q

What is mitochondrial inheritance?

A

Inheritance of genetic material in the mitochondria of maternal origin

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13
Q

Distribution of mitochondria in gametes?

A

Female : in the secondary oocyte

Male : in the tail of the spearmatozoa – lost after penetration

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14
Q

Features of Mitochondrial DNA

A
  1. Small genome : 16.6kBases
  2. Double stranded circular DNA
  3. 37 genes
  4. No introns
  5. Heteroplasmy : heterogeneity in DNA composition because one mitochondrion has many copies of DNA
  6. No repair mechanism so high mutation rate
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15
Q

What are the common sites of manifestation of abnormal mitochondrial inheritance?

A

Organs with high energy demand: muscle, brain, eyes

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16
Q

How many base pairs does a human genome have?

A

3000 million base pairs

  • 1.5% code for proteins
  • remaining : Junk DNA – control promoters, enchancer sequence
17
Q

Example of mitochondrial inheritance?

A

Leigh’s Disease

Mutation of mDNA MT-ATP 6 gene – defective ATP synthase – poor energy production in the motor area of the brain – progressive muscle weakness, respiratory & renal impairment, lactic acidosis, seizures, loss of motor skills

18
Q

Compare and contrast mDNA and nuclear DNA.

A
  1. Location : mDNA - in mitochondrion; nDNA - in nucleus
  2. Source of DNA : mDNA - mother ; nDNA - both parents
  3. Number of bases : mDNA - 16.6kB ; nDNA - 300 million base pairs
  4. Introns : mDNA - no ; nDNA - yes
  5. Functions of DNA : mDNA - for mitochondrial enzymes mainly ; nDNA - for all proteins in the body
19
Q

What is mosaicism?

A

New mutation acquired after fertilization.

20
Q

Types of mosaicism

A

Somatic and Gonadal

Somatic - affects somatic and germ cells eg: McCune Albright Syndrome

Gonadal - affects germ cells - somatic cells are normal

21
Q

What are imprinting disorders?

A

Expression of genes from just one allele because of modification to the DNA (epigenetics).

22
Q

Modification of histones and the effects.

A

+ Acetyl - activation
+ Methylation - deactivation
+ Phosphate - apoptosis

23
Q

Examples of imprinting disorders?

A
  1. Angelman syndrome
    - NORMAL : activation of maternal copy of the gene
    - ABNORMAL : deletion of maternal copy
    ~ learning difficulties
  2. Prader Willi Syndrome
    - NORMAL : paternal copy of the gene is active
    - ABNORMAL : deletion of paternal copy
    ~ hypotonia, overeating, learning difficulties, hypogonadism

Week 1 - Medical Genetics (5 decks)

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