WBR0123

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Genetics
Sub Category	SubCategory::Neurology, SubCategory::General Principles
Prompt	[[Prompt::A 15 year old girl is brought into clinic for evaluation by a medical geneticist. As an infant she displayed significant development delays in both cognitive and motor functioning. She was only able to walk alone at the age of 32 months. Her gait now is wide-based and she has notable ataxia. She is severely mentally retarded, with a vocabulary of approximately 20 words. She has a history of tonic seizures, which are sometimes accompanied by fever. Despite these symptoms she has a pleasant demeanor and laughs often without humorous stimulus.]]
Answer A	AnswerA::Deletion of maternal allele; methylation of paternal allele on chromosome 14
Answer A Explanation	[[AnswerAExp::Angelman syndrome is caused by deletion of the maternal allele and silencing of the paternal allele on chromosome 15.]]
Answer B	AnswerB::Deletion of paternal allele; methylation of maternal allele on chromosome 14
Answer B Explanation	[[AnswerBExp::Angelman syndrome is caused by deletion of the maternal allele and silencing of the paternal allele on chromosome 15.]]
Answer C	AnswerC::Deletion of maternal allele; methylation of paternal allele on chromosome 15
Answer C Explanation	[[AnswerCExp::Angelman syndrome is caused by deletion of the maternal allele and silencing of the paternal allele on chromosome 15.]]
Answer D	AnswerD::Deletion of paternal allele; methylation of maternal allele on chromosome 15
Answer D Explanation	[[AnswerDExp::Angelman syndrome is caused by deletion of the maternal allele and silencing of the paternal allele on chromosome 15.]]
Answer E	AnswerE::Methylation of two maternal alleles on chromosome 15
Answer E Explanation	[[AnswerEExp::Angelman syndrome is caused by deletion of the maternal allele and silencing of the paternal allele on chromosome 15.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::The patient in this vignette has Angelman syndrome. Angelman syndrome is a neuro-genetic disorder characterized by severe intellectual and developmental disability, sleep disturbance, seizures, jerky movements (especially hand-flapping), frequent laughter or smiling, and usually a happy demeanor. Angelman syndrome is caused by the deletion of the normal allele-specific expression of the maternal copy of several genes on chromosome 15 (imprinting). 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: Angelman syndrome is caused by deletion of the normally imprinted maternal allele on chromosome 15. References: First Aid 2104 page 85; First Aid 2012 page 88.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Angelman syndrome, WBRKeyword::Genetics
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::