WBR0975

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::A 6-months-old boy is brought by his mother to the emergency department (ED) for convulsions and vomiting. The mother states that her son has been healthy and has had an uneventual neonatal course. She also says he has been exclusively breastfed since birth. One day earlier, the pediatrician advised her to introduce soft foods in his diet, and the baby was fed small amounts of mashed bananas, apple juice, and carrot juice earlier today for the first time. The physician in the ED suspects this patient has an inborn error of metabolism caused by an enzyme deficiency. Which of the following compounds should be avoided in this patient's diet?]]
Answer A	AnswerA::Sucrose
Answer A Explanation	[[AnswerAExp::Sucrose is a disaccharide composed of glucose and fructose. Fructose and complex compounds that include fructose should be avoided among patients with fructose intolerance.]]
Answer B	AnswerB::Amylose
Answer B Explanation	[[AnswerBExp::Amylose is a polymer composed of D-glucose units. Amylose can be included in the diet of patients with fructose intolerance.]]
Answer C	AnswerC::Cellulose
Answer C Explanation	[[AnswerCExp::Cellulose is a polysaccharide that consists of a linear chain of linked D-glucose units. Humans cannot fully digest cellulose, and it is main bulking agent of human feces. Cellulose can be included in the diet of patients with fructose intolerance.]]
Answer D	AnswerD::Lactose
Answer D Explanation	[[AnswerDExp::Lactose is a disaccharide composed of glucose and galactose. Lactose can be included in the diet of patients with fructose intolerance.]]
Answer E	AnswerE::Maltose
Answer E Explanation	AnswerEExp::Maltose is a disaccharide composed of two molecules of glucose. Maltose can be included in the diet of patients with fructose intolerance.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Fructose intolerance is an autosomal recessive genetic disease of fructose metabolism. It is caused by a deficiency in the enzyme aldolase B that results in the accumulation of fructose 1-phosphate. The accumulation of fructose 1-phosphate inhibits glycogenolysis and gluconeogenesis due to the depletion of phosphate. The signs and symptoms of fructose intolerance include seizures, irritability, vomiting, jaundice, hypoglycemia (especially following fructose or sucrose intake), hyperuricemia, hepatosplenomegaly, and early gout, and cirrhosis if fructose is not eliminated from the diet. The treatment of this condition is the exclusion of fructose, sucrose (a disaccharide composed of glucose and fructose), and sorbitol from the diet. Shown below is a illustration of the reactions involved in fructose metabolism. Educational Objective: Fructose intolerance is an autosomal recessive disease caused by the deficiency in the enzyme aldolase B. Patients with fructose intolerance should exclude fructose, sucrose and sorbitol from their diet. References: Steinmann B, Santer R. Disorders of Fructose Metabolism. In: Saudubray JM, van den Berghe G, Walter JH, eds. Inborn Metabolic Diseases: Diagnosis and Treatment. 5th ed. New York, NY: Springer; 2012. First Aid 2014 page 106]]
Approved	Approved::Yes
Keyword	WBRKeyword::Fructose metabolism, WBRKeyword::Fructose intolerance, WBRKeyword::Glycogenolysis, WBRKeyword::Gluconeogenesis, WBRKeyword::Vomiting, WBRKeyword::Seizures, WBRKeyword::Hypoglycemia, WBRKeyword::Phosphate
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