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 in by his mother for a medical evaluation. His mother states that her child has suffered growth retardation, multiple blood clots in his leg and 2 bone fractures in his right arm and left femur in the past. You perform an ophthalmology exam and find a sublaxated lens in the front of his right eye. She shows you his last blood test and they are remarkable for a macrocyctic anemia. His mother is very frustrated and wants to know what’s wrong with her child. What is the most likely diagnosis of this child:]]
Answer A	AnswerA::Marfan syndrome
Answer A Explanation	[[AnswerAExp::The two diseases 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.]]
Answer B	AnswerB::Cystathionine beta-synthase deficiency
Answer B Explanation	[[AnswerBExp::Homocystinuria is an inherited metabolic disorder in methionine metabolism There are multiple forms of homocystinuria, which are distinguished by their signs and symptoms and 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. Another acronym for Homocystinuria is cystathionine beta synthase deficiency, which is also the etiology for the disease.]]
Answer C	AnswerC::Vitamin B12 deficiency
Answer C Explanation	AnswerCExp::B12 deficiency does not present in this constellation of symptoms and thus it's merely a distractor.
Answer D	AnswerD::Folic acid deficiency
Answer D Explanation	AnswerDExp::Folic acid deficiency does not present in this constellation of symptoms and thus it's merely a distractor.
Answer E	AnswerE::Riboflavin deficicency
Answer E Explanation	AnswerEExp::Riboflavin deficicency does not present in this constellation of symptoms and thus it's merely a distractor.
Right Answer	RightAnswer::B
Explanation	[[Explanation::Homocystinuria is an inherited metabolic disorder in methionine metabolism There are multiple forms of homocystinuria, which are distinguished by their signs and symptoms and 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. Another acronym for Homocystinuria is cystathionine beta synthase deficiency, which is also the etiology for the disease. The two diseases 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: References: ]]
Approved	Approved::Yes
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