WBR0123

Author	[[PageAuthor::William J Gibson (reviewed by Yazan Daaboul, M.D.)]]
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 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 past medical history is also significant for tonic seizures. Today, her gait is wide-based and she has notable ataxia. She is severely mentally retarded, with a vocabulary of approximately 20 words. Despite these symptoms she has a pleasant demeanor and laughs often without humorous stimulus. Which of the following genetic disorders is most likely responsible for the patient's condition?]]
Answer A	AnswerA::Deletion of a maternal-derived allele; methylation of a paternal-derived allele on chromosome 14
Answer A Explanation	[[AnswerAExp::Angelman syndrome is caused by deletion of the maternal-derived allele and silencing of the paternal-derived allele on chromosome 15.]]
Answer B	AnswerB::Deletion of paternal-derived allele; methylation of maternal-derived allele on chromosome 14
Answer B Explanation	[[AnswerBExp::Angelman syndrome is caused by deletion of the maternal-derived allele and silencing of the paternal-derived allele on chromosome 15.]]
Answer C	AnswerC::Deletion of maternal-derived allele; methylation of paternal-derived allele on chromosome 15
Answer C Explanation	[[AnswerCExp::Angelman syndrome is caused by deletion of the maternal-derived allele and silencing of the paternal-derived allele on chromosome 15.]]
Answer D	AnswerD::Deletion of paternal-derived allele; methylation of maternal-derived allele on chromosome 15
Answer D Explanation	[[AnswerDExp::Angelman syndrome is caused by deletion of the maternal-derived allele and silencing of the paternal-derived allele on chromosome 15.]]
Answer E	AnswerE::Methylation of two maternal-derived alleles on chromosome 15
Answer E Explanation	[[AnswerEExp::Angelman syndrome is caused by deletion of the maternal-derived allele and silencing of the paternal-derived allele on chromosome 15.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::Angelman syndrome (AS), also known as the "happy puppet" syndrome, is a neurodevelopmental disorder characterized by severe intellectual and developmental disability, sleep disturbance, seizures, jerky movements (especially hand-flapping), frequent laughter or smiling, love of water, and usually a happy demeanor. Prominent facial features also include protruding jaw and tongue, deep set eyes, wide mouth, and flat occiput with microcephaly. Angelman syndrome is most commonly caused by a deletions of in genes of maternal-derived alleles of chromosome 15. Other causes of AS include uniparental disomy for chromsome 15, imprinting (methylation) defect, and mutations within the gene that encode ubiquitin protein ligase (UBE3A). Educational Objective: Angelman syndrome is caused by deletion of the normally imprinted maternal-derived allele on chromosome 15. References: Clayton-Smith J, Laan L. Angelman syndrome: a review of the clinical and genetic aspects. J Med Genet. 2003;40:87-95. First Aid 2104 page 85]]
Approved	Approved::Yes
Keyword	WBRKeyword::Angelman syndrome, WBRKeyword::Genetics, WBRKeyword::Imprinting, WBRKeyword::Epigenetics, WBRKeyword::Chromosome 15
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