WBR0122

Author	[[PageAuthor::William J Gibson (reviewed by Rim Halaby, M.D. [1])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Genetics
Sub Category	SubCategory::Endocrine, SubCategory::General Principles
Prompt	[[Prompt::A 14 year old boy is brought to the clinic for evaluation by a genetics counselor. As a child, the boy slept more than usual, suffered strabismus, and most notably exhibited marked hyperphagia. Now, the boy suffers difficulties in school and has an IQ of 70. In addition to his intellectual deficits, he displays compulsive behaviors. He reports being constantly hungry and is morbidly obese due to hyperphagia throughout life. The most likely genetic syndrome which would explain the child’s symptoms is caused by which of the following?]]
Answer A	AnswerA::Deletion of maternal allele; methylation of paternal allele on chromosome 14
Answer A Explanation	[[AnswerAExp::Prader-Willi syndrome is caused by deletion of the paternal allele and imprinting of the maternal allele on chromosome 15.]]
Answer B	AnswerB::Deletion of paternal allele; methylation of maternal allele on chromosome 14
Answer B Explanation	[[AnswerBExp::Prader-Willi syndrome is caused by deletion of the paternal allele and imprinting of the maternal allele on chromosome 15.]]
Answer C	AnswerC::Deletion of maternal allele; methylation of paternal allele on chromosome 15
Answer C Explanation	[[AnswerCExp::Prader-Willi syndrome is caused by deletion of the paternal allele and imprinting of the maternal allele on chromosome 15.]]
Answer D	AnswerD::Deletion of paternal allele; methylation of maternal allele on chromosome 15
Answer D Explanation	[[AnswerDExp::Prader-Willi syndrome is caused by deletion of the normally imprinted paternal allele on chromosome 15.]]
Answer E	AnswerE::Methylation of two paternal alleles on chromosome 15
Answer E Explanation	[[AnswerEExp::Prader-Willi syndrome is caused by deletion of the paternal allele and imprinting of the maternal allele on chromosome 15.]]
Right Answer	RightAnswer::D
Explanation	[[Explanation::Prader-Willi syndrome is s a rare, genetic disorder in which seven genes (or some subset thereof) on chromosome 15 (q 11–13) are deleted or unexpressed (chromosome 15q partial deletion) on the paternal chromosome. This is an example of imprinting. Patients often exhibit poor muscle tone, short stature, incomplete sexual development, and obesity due to over-eating (hyperphagia). Wiki-Mnemonic: Prader-Willi syndrome is due to deletion of the Paternal allele. AngelMan syndrome is due to deletion of the Maternal allele. Educational Objective: Prader-Willi syndrome is caused by deletion of the normally imprinted paternal allele on chromosome 15. References: First Aid 2012 page 88.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Prader Willi, WBRKeyword::genetics
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::