WBR0144
| Author | [[PageAuthor::Rim Halaby, M.D. [1] (Edited by Will Gibson) (Reviewed by Alison Leibowitz)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Genetics |
| Sub Category | SubCategory::Musculoskeletal/Rheumatology |
| Prompt | [[Prompt::A 37-year-old male presents to the emergency department for severe sudden "tearing" chest pain that radiates to his back. The patient is tall, has abnormal joints laxity, and long extremities. A medical student suggests that this patient has Marfan syndrome, whereas the resident in the ER contends that long extremities and joint laxity are features of other inherited conditions. Which of the following can explain the resident’s argument?]] |
| Answer A | AnswerA::Mosaicism |
| Answer A Explanation | [[AnswerAExp::Mosaicism denotes the presence of two or more populations of cells with different genotypes in one individual who has developed from a single fertilized egg.
Different types of mosaicism exist, such as gonadal mosaicism (restricted to the gametes) and tissue or somatic mosaicism.]] |
| Answer B | AnswerB::Heteroplasmy |
| Answer B Explanation | [[AnswerBExp::Heteroplasmy is the presence of more than one type of an organellar genome (mitochondrial DNA or plastid DNA), within a cell or individual. Heteroplasmy is a factor for the severity of mitochondrial diseases.]] |
| Answer C | AnswerC::Pleiotropy |
| Answer C Explanation | [[AnswerCExp::Pleiotropy occurs when one gene influences multiple phenotypic traits. Consequently, a mutation in a pleiotropic gene may have an effect on some or all traits simultaneously. While the Fibrillin mutations of Marfan syndrome are illustrations of pleiotropy, pleiotropy is not the most accurate descriptor of the resident's argument.]] |
| Answer D | AnswerD::Locus heterogeneity |
| Answer D Explanation | [[AnswerDExp::Locus heterogeneity is a single disorder, trait, or pattern of traits caused by mutations in genes at different chromosomal loci. This patient’s marfanoid habitus can be result from Marfan syndrome, homocysteinuria, or MEN 2 B syndrome.]] |
| Answer E | AnswerE::Variable expression |
| Answer E Explanation | AnswerEExp::Variable expression occurs when a phenotype is expressed to a different degree among individuals with the same genotype. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::The patient in this vignette has most likely suffered aortic dissection due to Marfan syndrome. Patients with marfanoid habitus are usually tall, have abnormal joints laxity and long extremities and limbs. Marfanoid habitus can be caused by Marfan syndrome, homocysteinuria or MEN 2 B syndrome. This is an example of locus heterogeneity. Educational Objective: Locus heterogeneity is a single disorder, trait, or pattern of traits caused by mutations in genes at different chromosomal loci. Marfanoid habitus is an example of locus heterogeneity. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Marfan, WBRKeyword::Marfan syndrome, WBRKeyword::Marfan's syndrome, WBRKeyword::Pleiotropy |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |