A 26-Year-Old Woman Is Being Evaluated for a Possible Inherited

question 13

Multiple Choice

A 26-year-old woman is being evaluated for a possible inherited disorder.  She has a 6-year history of generalized tonic-clonic seizures, and a year ago, she had partial loss of vision due to an occipital infarction.  Her mother has chronic intermittent muscle weakness and lactic acidosis, and her maternal uncle has hemiplegia.  Skeletal muscle biopsy of the patient shows ragged-appearing muscle fibers.  After further evaluation, all the affected family members are found to suffer from the same inherited disease.  Pedigree analysis is shown in the image below. Which of the following is the most likely explanation for the variability of clinical manifestations in the affected family members?

• A)Anticipation
• B)Heteroplasmy
• C)Incomplete penetrance
• D)Mosaicism
• E)Uniparental disomy

---

Definitions:

Microorganism

A microscopic organism, such as a bacteria, virus, or fungus, that can be found in a wide range of environments.

DNA Segment

A specific sequence of DNA within a chromosome characterized by a particular function or genetic information.

Reverse Transcription

The process by which the information contained in RNA molecules is transcribed into DNA molecules.

DNA Ligase

An agent that supports the unification of DNA strands by enabling the production of a phosphodiester bond.