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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{Rim}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|Prompt=A 1-year-old boy is brought by his mother to the pediatrician for a scheduled vaccine appointment and general check up.  As the pediatrician is examining the baby, he holds a toy in his hand in order to get the baby’s attention.  The pediatrician notices that the baby is unable to follow the toy with his eyes.  Upon questioning the mother, she reports that her son is unable to follow with his eyes the baby hanging bell toys on top of his beds.  She also tells the pediatrician that her son does not interact with people around him as if he does not see them. Physical exam reveals no other abnormalities and the growth chart depicts a normal development of the baby.  The pediatrician suspects a metabolic disorder and requests a radiolabeled 14C galactose analysis.  Enzyme deficiency in which of the following steps of galactose metabolism is most likely?
|Prompt=A 1-year-old boy is brought to the pediatrician for a well-child visit.  During the physical examination, the pediatrician notices that the baby is unable to follow his gestures with his eyes.  Upon further questioning, the mother reports that her son is not very interactive with people and does not seem to be intrigued by what is going on around him. The child is otherwise healthy and growing adequately.  The pediatrician suspects a metabolic disorder and requests a radiolabeled <sup>14</sup>C galactose analysis.  Which of the following enzyme deficiencies is most likely present?
|Explanation=[[Galactokinase deficiency]] is a mild autosomal recessive galactose metabolism disorder.  It is characterized by the accumulation of galactose in the blood and urine and elevated levels of [[galacticol]]. The accumulation of galacticol is associated with the occurrence of cataracts resulting in decreased vision that can be suspected by the inability of the patients to track objects with their eyes and absence of social smiling.  Galactokinase deficiency is different from the more severe [[classic galactosemia]] and is not associated with mental retardation, failure to thrive and severe symptoms of jaundice and vomiting.


Educational objective:
[[File:WBR0910.png]]
Galactokinase deficiency is a mild galactose metabolism disorder leading to accumulation of galacticol and subsequent formation of cataract.  It is different from the more severe classic galactosemia that is associated with mental retardation, failure to thrive and severe symptoms of jaundice and vomiting.
|Explanation=[[Galactokinase deficiency]] is a mild autosomal recessive galactose metabolism disorder.  It is characterized by the accumulation of galactose in the blood and urine and elevated levels of galacticol. The accumulation of galacticol is associated with the occurrence of cataracts resulting in decreased vision that can be suspected by the inability of the patients to track objects with their eyes and absence of social smiling.  Galactokinase deficiency is different from the more severe classic galactosemia and is not associated with mental retardation, failure to thrive and severe symptoms of jaundice and vomiting.


Reference: V. Schwarz. Disorders of galactose metabolism. J Clin Pathol Suppl (Assoc Clin Pathol). 1969; 2: 72–75.  
[[File:Galactose_metabolism_disorders.png|700px]]
|AnswerA=A
|AnswerA=A
|AnswerAExp=Galactokinase deficiency is characterized by the accumulation of galactose in the blood and urine and elevated levels of galacticol. The accumulation of [[galacticol]] is associated with the occurrence of cataracts in the absence of mental retardation, failure to thrive and severe symptoms of jaundice and vomiting.
|AnswerAExp=Galactokinase deficiency is characterized by the inability to transform galactose into galactose-1-phosphate with subsequent accumulation of galacticol. It is a relatively benign disorder, with galacticol accumulation leading to early-onset cataracts if the proper diet adjustments are not made.
|AnswerB=B
|AnswerB=B
|AnswerBExp=[[Classic galactosemia]] is an autosomal recessive disease characterized by the absence of galactose 1 phosphate uridyltransferase (GALT) resulting in the accumulation of galactose 1 phosphate, galactose and galacticol.  The diagnosis of this patient is galactokinase deficiency and not classic galactosemia.  Galactokinase deficiency is different from the more severe classic galactosemia and is not associated with mental retardation, failure to thrive and severe symptoms of jaundice and vomiting.
|AnswerBExp=Classic galactosemia is an autosomal recessive disease characterized by the absence of galactose-1-phosphate uridyltransferase (GALT) resulting in the accumulation of galactose-1-phosphate, galactose and galacticol.  Although classic galactosemia is associated with cataracts, it is a more severe illness associated with mental retardation, failure to thrive and jaundice.
|AnswerC=C
|AnswerC=C
|AnswerCExp=UDP glactose 4 epimerase ([[GALE]]) catalyzes the conversion of UDP galactose to UDP [[glucose]]. Deficiency in GALE results in a spectrum of symptoms, the most severe of which are a constellation of symptoms similar to classic galactosemia. The presentation of this patient is mild and is only characterized by the presence of visual deficit.  the visual deficit is suggestive of the presence of [[cataract]] resulting from [[galacticol]] accumulation due to [[galactokinase deficiency]].
|AnswerCExp=UDP-galactose-4-epimerase (GALE), also known as UDP-glucose-4-epimerase, catalyzes the reversible conversion of UDP-galactose to UDP-glucose. The deficiency of this enzyme results in symptoms similar to those of classic galactosemia.
|AnswerD=D
|AnswerD=D
|AnswerDExp=Aldose reductase converts galactose to galacticol.  Its deficiency does not lead to cataracts. On the opposite, overproduction of galacticol lead to cataract.
|AnswerDExp=Aldose reductase converts galactose to galacticol.  Its deficiency does not lead to cataracts. Based on animal models, it is hypothesized that the lower the expression of aldose reductase the better the individual is protected from cataracts and atherosclerotic cardiovascular disease.
|AnswerE=E
|AnswerE=E
|AnswerEExp=UDP glucose pyrophosphate converts UDP glucose to glucose 1 phosphate. The patient's presentation is more suggestive of galactokinase deficiency.
|AnswerEExp=UDP-glucose-pyrophosphorylase converts UDP glucose to glucose-1-phosphate. This deficiency is yet to be reported among humans, or is likely benign and asymptomatic.
|EducationalObjectives=Galactokinase deficiency is characterized by the inability to transform galactose into galactose-1-phosphate with subsequent accumulation of galacticol. It is a relatively benign disorder, with galacticol accumulation leading to early-onset cataracts if the proper diet adjustments are not made.
|References=V. Schwarz. Disorders of galactose metabolism. J Clin Pathol Suppl (Assoc Clin Pathol). 1969; 2: 72–75.
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=Galactose, Galactosemia, galactokinase, galactokinase deficiency
|WBRKeyword=Galactose, Galactosemia, galactokinase, galactokinase deficiency
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 02:03, 28 October 2020
Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Serge Korjian)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Biochemistry
Sub Category SubCategory::General Principles
Prompt [[Prompt::A 1-year-old boy is brought to the pediatrician for a well-child visit. During the physical examination, the pediatrician notices that the baby is unable to follow his gestures with his eyes. Upon further questioning, the mother reports that her son is not very interactive with people and does not seem to be intrigued by what is going on around him. The child is otherwise healthy and growing adequately. The pediatrician suspects a metabolic disorder and requests a radiolabeled 14C galactose analysis. Which of the following enzyme deficiencies is most likely present?

]]

Answer A AnswerA::A
Answer A Explanation [[AnswerAExp::Galactokinase deficiency is characterized by the inability to transform galactose into galactose-1-phosphate with subsequent accumulation of galacticol. It is a relatively benign disorder, with galacticol accumulation leading to early-onset cataracts if the proper diet adjustments are not made.]]
Answer B AnswerB::B
Answer B Explanation [[AnswerBExp::Classic galactosemia is an autosomal recessive disease characterized by the absence of galactose-1-phosphate uridyltransferase (GALT) resulting in the accumulation of galactose-1-phosphate, galactose and galacticol. Although classic galactosemia is associated with cataracts, it is a more severe illness associated with mental retardation, failure to thrive and jaundice.]]
Answer C AnswerC::C
Answer C Explanation AnswerCExp::UDP-galactose-4-epimerase (GALE), also known as UDP-glucose-4-epimerase, catalyzes the reversible conversion of UDP-galactose to UDP-glucose. The deficiency of this enzyme results in symptoms similar to those of classic galactosemia.
Answer D AnswerD::D
Answer D Explanation [[AnswerDExp::Aldose reductase converts galactose to galacticol. Its deficiency does not lead to cataracts. Based on animal models, it is hypothesized that the lower the expression of aldose reductase the better the individual is protected from cataracts and atherosclerotic cardiovascular disease.]]
Answer E AnswerE::E
Answer E Explanation AnswerEExp::UDP-glucose-pyrophosphorylase converts UDP glucose to glucose-1-phosphate. This deficiency is yet to be reported among humans, or is likely benign and asymptomatic.
Right Answer RightAnswer::A
Explanation [[Explanation::Galactokinase deficiency is a mild autosomal recessive galactose metabolism disorder. It is characterized by the accumulation of galactose in the blood and urine and elevated levels of galacticol. The accumulation of galacticol is associated with the occurrence of cataracts resulting in decreased vision that can be suspected by the inability of the patients to track objects with their eyes and absence of social smiling. Galactokinase deficiency is different from the more severe classic galactosemia and is not associated with mental retardation, failure to thrive and severe symptoms of jaundice and vomiting.


Educational Objective: Galactokinase deficiency is characterized by the inability to transform galactose into galactose-1-phosphate with subsequent accumulation of galacticol. It is a relatively benign disorder, with galacticol accumulation leading to early-onset cataracts if the proper diet adjustments are not made.
References: V. Schwarz. Disorders of galactose metabolism. J Clin Pathol Suppl (Assoc Clin Pathol). 1969; 2: 72–75.]]

Approved Approved::Yes
Keyword WBRKeyword::Galactose, WBRKeyword::Galactosemia, WBRKeyword::galactokinase, WBRKeyword::galactokinase deficiency
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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