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Chapter 13. Disorders of Organelles

Which of the following is a characteristic of mitochondrial inheritance?

A. Male-to-male transmission.

B. Replicative segregation.

C. Expression in homozygotes.

D. A spontaneous mutation rate lower than that of nuclear genes.

E. Bottlenose phenomenon.

B is the correct answer.

  • A. Mitochondrial inheritance shows maternal transmission.

  • C. Homozygous and heterozygous are terms applied to nuclear genes. Mitochondrial DNA patterns are described as showing homoplasmy or heteroplasmy.

  • D. Mitochondrial genes have a higher mutation rate than the nuclear genes.

  • E. The correct term is 'bottleneck' phenomenon.

A patient (20-year-old woman) presents to your clinic wanting to be tested for a mitochondrial disorder. She tells you that her bother has been diagnosed with a mitochondrial disorder. You would tell her which of the following?

A. Because her brother is affected, and the condition is mitochondrial, she could not be affected.

B. Since she does not have any symptoms now as a young adult, she could not be affected.

C. If she has the same condition as her brother, she should be affected to the same degree as he is.

D. The most helpful information would be to know the particular mutation that is present in her brother.

E. She should not have any children and should have a sterilization procedure soon.

D is the correct answer.

  • A. Clearly she could be affected by any number of mechanisms–either nuclear gene (Mendelian) inheritance or a mtDNA mutation she inherits from her mother.

  • B. Mitochondrial disorders may have adult onset.

  • C. Mitochondrial disorders exhibit highly variable expression including intra-familial variation.

  • E. Of course patient centered counseling would never make such a recommendation.

You are evaluating a child with multisystem problems. As you ponder ordering some diagnostic tests, you could appropriately decide which of the following?

A. Because the child has chronic respiratory problems you should test for peroxisomal disorders.

B. Perform a renal biopsy.

C. Because the child is showing severe premature aging, you should do testing for genes coding for the nuclear membrane proteins.

D. You can safely assume the condition is autosomal dominant and counsel as such—avoiding doing any tests.

E. Because multiple organ systems are involved, testing won't ...

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