Genetics Case Problems

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Genetics Case Problems

• SF 36
• R. Daniel Gietz Ph.D

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Learning Objectives.

• Using the following case scenario the students
  will
• 1. Appreciate the clinical variability in genetic
  disorders.
• 2. Understand the importance of a family history
  in genetic disorders.
• 3. Learn about the application of DNA diagnostic
  tests, their advantages, limitations and the
  ethical issues.

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Diagnosis

• A clinical diagnosis of OTC (Ornithine
  Transcarbamylase deficiency) deficiency in Laura
  was made by the metabolic specialist based on
  above investigations.

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Questions

• Question 1. Which metabolic pathway is involved
  in this disorder?
• a) Krebs cycle
• b) Urea cycle

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Questions

• Question 2. What is the inheritance of this
  disorder?
• A) Autosomal dominant
• b) X-linked
• c) Autosomal recessive

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X linked inheritance
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Questions

• Question 3. Is the mother (Helen) also
  affected?
• a)Yes
• b)No

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Questions

• Question 4. Which organ is primarily involved in
  this metabolic disorder?
• a) Brain
• b) Liver
• c) Kidney

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Questions

• Question 5. Can you explain the reason why the
  mother and daughter have different symptoms?

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X inactivation

• Females have 2 X chromosomes. Most genes on one
  of them are inactive. This is called X
  inactivation or lyonization. Either the maternal
  or paternal X could be inactive. Occurs in
  embryogenesis and is random. Females are mosaics
  there some cells have one X some the other active.

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Questions

• Question 6. If the mother is also affected what
  is her risk of having an affected boy?

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Questions

• Question 7. Why are boys with this disorder
  severely affected?

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Questions

• Question 8. With the recent gain in knowledge
  the physicians have obtained the DNA from Laura
  instead of an invasive biopsy procedure. Please
  see a copy of the attached DNA report from Laura.
  

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Questions

• a) What is the difference between disease causing
  mutation and polymorphism?
• b) How do the Molecular geneticists confirm if it
  is a disease causing mutation?
• c) If this is indeed a disease causing mutation,
  which class of mutation will this be?
• a) Large deletion
• b) Nonsense mutation
• c)Missense mutation

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Questions

• d) As seen in the DNA report the testing was done
  using direct detection by PCR amplification of
  the ten exons of OTC gene. However linkage
  analysis can also be performed. What are some of
  the advantages and disadvantages of each method?

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Questions

• Question 9. The mother wants no DNA testing, as
  she is afraid this might affect her insurability.
  How will you address this problem?

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Questions

• Question 10. Based on the DNA results, you want
  to test Lauras sister as well. The DNA test is
  very expensive and has to be sent to a laboratory
  in the United States. What will your arguments
  be to convince your laboratory director to pursue
  with this testing?

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