WBR0782

Author	[[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]]
Exam Type	USMLE Step 1
Main Category	Pathophysiology
Sub Category	Head and Neck, Oncology
Prompt	[[Prompt::A 1-week-old boy is brought to the pediatric clinic for a well-baby checkup. The mother reports that her child has been doing well since he has been home. He was born full-term via normal vaginal delivery without any perinatal complications. His first physical exam was unremarkable according to the hospital charts. He has been exclusively breast fed and tolerating several feeds a day. On physical exam, all seems within normal limits, but the pediatrician notices something unusual on eye exam (shown below). Which of the following mutations can explain the findings in this child? ]]
Answer A	Elastin gene mutation
Answer A Explanation	Elastin mutations are involved in the pathogenesis of Marfan's syndrome.
Answer B	Retinoblastoma gene mutation
Answer B Explanation	Retinoblastoma gene mutations are responsible for development of retinoblastoma which can cause leukocoria.
Answer C	FGFR3 gene mutation
Answer C Explanation	FGFR3 gene mutations are responsible for achodroplasia.
Answer D	Collagen gene mutation
Answer D Explanation	Collagen gene mutations are seen in patients with osteogenesis imperfecta.
Answer E	p53 gene mutation
Answer E Explanation	p53 gene mutations are responsible for the development of several cancers including osteosarcoma, breast and colon cancer.
Right Answer	B
Explanation	Leukocoria refers to an abnormal white reflection from the retina where a usual red reflex is expected. Leukocoria in infants raises concern for two important entities: congenital cataracts and retinoblastoma. Retinoblastoma is a rapidly progressing tumor that develops from cells of a retina. It can either be sporadic or inherited. In both cases, the tumor develops due to a mutation in the RB1 gene whose protein product, the retinoblastoma protein, is a tumor suppressor that inhibits G1-to-S transition and regulates the cell cycle. In its inherited form, the mutation of the RB1 gene predisposes to other malignancies later in life. Educational Objective: Leukocoria is an abnormal white reflex that can be seen in children with retinoblastoma. Retinoblastoma occurs due to a mutation in the RB1 gene. References: Abramson DH, Frank CM, Susman M, Whalen MP, Dunkel IJ, Boyd NW. Presenting signs of retinoblastoma. J Pediatr. 1998;132(3 Pt 1):505-8.
Approved	Yes
Keyword	Retinoblastoma, Leukocoria, White reflex, Rb
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