WBR0166

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 2 CK
Main Category	MainCategory::Pediatrics
Sub Category	SubCategory::Genetics
Prompt	[[Prompt::A 7-year-old female is brought to her physician by her mother after the mother noticed her daughter began menstruating in the past month. The patient’s history is notable for several bone fractures throughout childhood and a “birthmark” that is pictured from a previous visit below. Bony abnormalities in this condition are caused by which of the following?]]
Answer A	AnswerA::Increased osteoclastic activity
Answer A Explanation	[[AnswerAExp::Incorrect: Osteoporosis involves an imbalance between bone resorption and bone formation, leading to poor mineralization and fragility of the bone. Increased osteoclastic activity causes osteoporosis.]]
Answer B	AnswerB::Decreased mineralization of osteoid
Answer B Explanation	[[AnswerBExp::Incorrect: Decreased mineralization of osteoid causes rickets which is a softening of the bones in children potentially leading to fractures and deformity. The predominant cause is a vitamin D deficiency, but lack of adequate calcium in the diet may also lead to rickets.]]
Answer C	AnswerC::Inappropriately increased PTH secretion
Answer C Explanation	[[AnswerCExp::Incorrect: Primary hyperparathryroidism can cause osteitis fibrosa cystica.]]
Answer D	AnswerD::Increased osteoblastic and osteoclastic activity
Answer D Explanation	[[AnswerDExp::Incorrect: Paget’s disease of bone is caused by increased bone turnover.]]
Answer E	AnswerE::Replacement of bone with fibrous tissue
Answer E Explanation	[[AnswerEExp::Correct: Polyostotic fibrous dysplasia is a feature of McCune Albright Syndrome.]]
Right Answer	RightAnswer::E
Explanation	[[Explanation::McCune-Albright syndrome (polyostotic fibrous dysplasia) is a genetic disorder of bones, skin pigmentation, and hormonal problems characterized by precocious puberty, unilateral cafe au lait spots and polyostotic fibrous dysplasia. The syndrome shows a broad spectrum of severity. The disease frequently involves the skull and facial bones, pelvis, spine, and shoulder girdle. The sites of involvement are the femur (91%), tibia (81%), pelvis (78%), ribs, skull and facial bones (50%), upper extremities, lumbar spine, clavicle, and cervical spine, in decreasing order of frequency. The craniofacial pattern of the disease occurs in 50% of patients with the polyostotic form of fibrous dysplasia. Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::McCune-Albright syndrome
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