WBR0098

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Genetics
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 36 year old woman presents to her physician for the gradual onset of uncontrolled spastic movements. She reports having begun experiencing mood disturbances and difficulty performing her job at work 3 months prior to the onset of her movement disorder began. Further questioning reveals that her father died of a neurodegenerative condition at the age of 50. The patient has researched her likely condition on the internet and is most concerned about having passed the trait onto her kids. She inquires about genetic testing. Which of the following would one expect to find in this patient?]]
Answer A	AnswerA::Loss of function mutation
Answer A Explanation	AnswerAExp::Incorrect - Huntington’s disease is caused by a trinucleotide expansion
Answer B	AnswerB::Expansion of CAA repeats
Answer B Explanation	AnswerBExp::ncorrect - This repeat is expanded in Friedreich’s ataxia
Answer C	AnswerC::Expansion of CAG repeats
Answer C Explanation	AnswerCExp::Correct - See Explanation.
Answer D	AnswerD::Expansion of CGG repeats
Answer D Explanation	AnswerDExp::Incorrect - This repeat is expanded in Fragile X Syndrome
Answer E	AnswerE::Expansion of CTG repeats
Answer E Explanation	AnswerEExp::Incorrect - This repeat is expanded in Myotonic dystrophy
Right Answer	RightAnswer::C
Explanation	[[Explanation::Huntington's disease (HD) is a neurodegenerative genetic disorderthat affects muscle coordination and leads to cognitive decline andpsychiatric problems. It typically becomes noticeable in mid-adult life. HD is the most common genetic cause of abnormal involuntary writhing movements called chorea, which is why the disease used to be called Huntington's chorea. The Huntingtin gene provides the genetic information for a protein that is also called "huntingtin". Expansion of a CAG triplet repeat stretch within the Huntingtin gene results in a different (mutant) form of the protein, which gradually damages cells in the brain, through mechanisms that are not fully understood. The disease is inherited in an autosomal dominant manner and displays genetic anticipation: earlier onset of disease in successive generations. This anticipation is caused by expansion of the repeat segment, which increases disease severity. Huntington’s disease is uniformly fatal. References: First Aid page 90,92,439 Educational Objective: References: ]]
Approved	Approved::Yes
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