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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor={{Rim}} (Reviewed by {{YD}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Biochemistry
|MainCategory=Biochemistry
Line 8: Line 8:
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
Line 20: Line 21:
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|Prompt=A previously healthy 6 months old boy was brought by his mother to the emergency department for vomiting and pallor. The mother reports that her son was normal at birth and his growth in height and weight meet the normal rate of growth of babies of his age. The baby was breastfed since his birth until a few days ago when the pediatrician advised her to start introducing some soft food in his diet.  The mother reports feeding the baby with a small amount of mashed fruits such as bananas or some apple or carrot juice. Which of the following should be avoided in the diet in order to prevent the occurrence of the symptoms in this boy?
|Prompt=A 6-months-old boy is brought by his mother to the emergency department for vomiting and pallor. 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. Which of the following compounds should be avoided in this patient's diet?
|Explanation=The baby presents with nausea, vomiting and pallor following ingestion of fruits for the first time in his life.  This is a typical presentation of [[fructose intolerance]], an autosomal recessive genetic disease of [[fructose metabolism]]. Fructose intolerance is caused by a deficiency in the enzyme aldolase B, leading to the accumulation of fructose 1-phosphate. The accumulation of fructose 1-phosphate inhibits [[glycogenolysis]] and [[gluconeogenesis]] due to the depletion of [[phosphate]]. The symptoms of fructose intolerance include [[hypoglycemia]], vomiting, [[jaundice]] and [[cirrhosis]] if fructose is not eliminated from the diet. The treatment of this condition is the exclusion of fructose, sucrose (a disaccharide formed by glucose and fructose) and [[sorbitol]] from the diet. Shown below is a diagram depicting fructose metabolism.
|Explanation=[[Fructose intolerance]] is an autosomal recessive genetic disease of [[fructose metabolism]]. It is mainly caused by a deficiency in the enzyme aldolase B and results in the accumulation of fructose 1-phosphate. The accumulation of fructose 1-phosphate inhibits [[glycogenolysis]] and [[gluconeogenesis]] due to the depletion of [[phosphate]] due to the accumulation of fructose-1-phosphate. The signs and symptoms of fructose intolerance include seizures, irritability, vomiting, [[jaundice]], hypoglycemia (especially following fructose or sucrose intake), hyperuricemia, hepatosplenomegaly, and early [[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.<br>
 
[[File:Fructose Metabolism.png|600px]]
[[File:Fructose Metabolism.png]]
 
'''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.


'''Reference:'''
First aid for USMLE step 1, 2013. Page 104.
|AnswerA=Sucrose
|AnswerA=Sucrose
|AnswerAExp=[[Sucrose]] is a disaccharide formed of [[glucose]] and [[fructose]]. Fructose should be avoided in the diet of patients with [[fructose intolerance]]; therefore, this patient should avoid sucrose in his diet.
|AnswerAExp=[[Sucrose]] is a disaccharide composed of [[glucose]] and [[fructose]]. Fructose, including complex compounds that include fructose, should be avoided among patients with [[fructose intolerance]].
|AnswerB=Amylose
|AnswerB=Amylose
|AnswerBExp=[[Amylose]] is a spiral polymer made up of D-glucose units. This polysaccharide is one of the two components of [[starch]]. Amylose can be included in the diet of patients with fructose intolerance.
|AnswerBExp=[[Amylose]] is a polymer composed of D-glucose units. Amylose can be included in the diet of patients with fructose intolerance.
|AnswerC=Cellulose
|AnswerC=Cellulose
|AnswerCExp=[[Cellulose]] is a polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall of green plants.  Humans can digest cellulose to some extent; however, it mainly acts as a hydrophilic bulking agent for feces and is often referred to as "dietary fiber". Cellulose can be included in the diet of patients with fructose intolerance.
|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.
|AnswerD=Lactose
|AnswerD=Lactose
|AnswerDExp=[[Lactose]] is a disaccharide formed of [[glucose]] and [[galactose]]. Lactose can be included in the diet of patients with [[fructose intolerance]].
|AnswerDExp=[[Lactose]] is a disaccharide composed of [[glucose]] and [[galactose]]. Lactose can be included in the diet of patients with [[fructose intolerance]].
|AnswerE=Maltose
|AnswerE=Maltose
|AnswerEExp=Maltose is a disaccharide formed of two molecules of glucose. Maltose can be included in the diet of patients with fructose intolerance.
|AnswerEExp=Maltose is a disaccharide composed of two molecules of glucose. Maltose can be included in the diet of patients with fructose intolerance.
|EducationalObjectives=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.<br>
First Aid 2014 page 106
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=Fructose metabolism, fructose intolerance
|WBRKeyword=Fructose metabolism, Fructose intolerance, Glycogenolysis, Gluconeogenesis, Vomiting, Seizures, Hypoglycemia, Phosphate
|Approved=No
|Approved=Yes
}}
}}

Revision as of 19:06, 10 March 2015
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 for vomiting and pallor. 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. 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, including 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 mainly caused by a deficiency in the enzyme aldolase B and results in the accumulation of fructose 1-phosphate. The accumulation of fructose 1-phosphate inhibits glycogenolysis and gluconeogenesis due to the depletion of phosphate due to the accumulation of fructose-1-phosphate. The signs and symptoms of fructose intolerance include seizures, irritability, vomiting, jaundice, hypoglycemia (especially following fructose or sucrose intake), hyperuricemia, hepatosplenomegaly, and early 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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