WBR0126

Author	PageAuthor::Mahmoud Sakr M.D.
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category
Prompt	[[Prompt::A 3-year-old male child is brought by his mother for medical evaluation. His mother states that her child has suffered growth retardation, multiple blood clots in his legs and bone fractures in his right arm and left femur in the past. An ophthalmology exam reveals sublaxated lens of the right eye. The patient's last performed blood test is remarkable for a macrocyctic anemia. The mother is very frustrated and wants to know what’s wrong with her child. What is the most likely diagnosis?]]
Answer A	AnswerA::Marfan syndrome
Answer A Explanation	[[AnswerAExp::Homocystinuria and Marfan's syndrome are clinically similar but florid arachnodactyly and scoliosis are commoner in Marfan's syndrome, whereas widening of epiphyses and metaphyses of long bones is a distinctive feature of homocystinuria. Mental retardation are uncommon in Marfan's syndrome. Patients with Marfan's syndrome do not have osteoporosis and may have excessively tall vertebrae.]]
Answer B	AnswerB::Cystathionine beta-synthase deficiency
Answer B Explanation	AnswerBExp::Homocystinuria is an inherited metabolic disorder in methionine metabolism. Homocystinuria is caused by cystathionine beta synthase deficiency.
Answer C	AnswerC::Vitamin B12 deficiency
Answer C Explanation	AnswerCExp::B12 deficiency does not cause the symptoms and signs in the patient in the vignette.
Answer D	AnswerD::Folic acid deficiency
Answer D Explanation	AnswerDExp::B12 deficiency does not cause the symptoms and signs in the patient in the vignette.
Answer E	AnswerE::Riboflavin deficicency
Answer E Explanation	AnswerEExp::B12 deficiency does not cause the symptoms and signs in the patient in the vignette.
Right Answer	RightAnswer::B
Explanation	[[Explanation::Homocystinuria is an inherited metabolic disorder in the methionine metabolism. There are multiple forms of homocystinuria which are distinguished by their signs and symptoms as well as their genetic cause. The most common form of homocystinuria is characterized by nearsightedness (myopia), dislocation of the lens at the front of the eye, an increased risk of abnormal blood clotting, and brittle bones that are prone to fracture (osteoporosis) or other skeletal abnormalities. Some affected individuals also have developmental delay and learning problems. Mutations in the CBS, MTHFR, MTR, MTRR, and MMADHC genes cause homocystinuria. Homocystinuria is caused by cystathionine beta synthase deficiency, which is also the etiology for the disease. Homocystinuria and Marfan's syndrome are clinically similar but florid arachnodactyly and scoliosis are commoner in Marfan's syndrome, whereas widening of epiphyses and metaphyses of long bones is a distinctive feature of homocystinuria. Mental retardation and thrombosis are common in homocystinuria and uncommon in Marfan's syndrome. Patients with homocystinuria frequently have osteoporosis at a young age with a high incidence of vertebral involvement including biconcavity and flattening. Patients with Marfan's syndrome do not have osteoporosis and may have excessively tall vertebrae. Educational Objective: Homocystinuria is caused by cystathionine beta synthase deficiency. References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Homocystinuria, WBRKeyword::marfan syndrome, WBRKeyword::cystathionine beta synthase deficiency
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::