WBR0277
| Author | [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Genetics, MainCategory::Pathology |
| Sub Category | SubCategory::Oncology |
| Prompt | [[Prompt::An 18- year old complains of bone pains and swelling over the right leg just above the knee. He has been losing weight progressively over the past 2 months. Past medical history is significant of having been treated for a cancer of the eye at the age of 3 years. Which of these genes is most likely responsible for these conditions in this patient?]] |
| Answer A | AnswerA::TP53 gene |
| Answer A Explanation | AnswerAExp::Incorrect. The TP53 suppressor gene is associated with DNA repair in the G1 to S phase of the cell cycle and associated with Li – Fraumeni syndrome |
| Answer B | AnswerB::RB gene |
| Answer B Explanation | AnswerBExp::Correct. See explanation |
| Answer C | AnswerC::Myc gene |
| Answer C Explanation | AnswerCExp::Incorrect. The Myc gene is a proto-oncogene that is of 2 types, L Myc associated with lung cancer and N Myc associated with neuroblastoma. These are involved with nuclear transcription |
| Answer D | AnswerD::Abl gene |
| Answer D Explanation | AnswerDExp::Incorrect. The Abl gene is associated with chronic myeloid leukemia (CML) |
| Answer E | AnswerE::Ret gene |
| Answer E Explanation | AnswerEExp::Incorrect. The Ret gene is associated with multiple endocrine neoplasia (MEN) types II and III |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::This is a case of Osteosarcoma with a past history of Retinoblastoma associated with the RB suppressor gene on chromosome 13. Osteosarcoma commonly affects men 10-20 years of age, found in the metaphysis of long bones often around the distal femur, proximal tibial region (knee). It is a connective tissue tumor arising from osteocytes.
Inactivation of the RB suppressor gene may be inherited as an autosomal dominant trait or it may be sporadic. In the inherited type, one of the alleles on chromosome 13 is inactivated in utero. After birth, only one additional mutation can occur on the remaining allele to cause cancer (called the one-hit theory) and then a patient is at risk of developing a Retinoblastoma, the most common malignancy of the eye in children. There is an additional increased risk for developing osteosarcoma between the age group of 10-25 years. Educational Objective The RB suppressor gene on chromosome 13 is associated with the bone and eye conditions Osteosarcoma and Retinoblastoma. Reference: First Aid for the USMLE step 1 2011 edition Pgs 227-8 |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |