WBR270

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [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 3-year-old boy is brought to the physician’s office with a 3-day history of fever, cough, and runny nose. The mother states that the child is not growing like his siblings before him. Physical examination is remarkable for generalized hypotonia, restricted joint movements, and coarse facial features. Radiographic findings include bullet-shaped phalanges, wedging of the vertebrae, and widening and thickening of the ribs. Which of the following statements is true regarding the impaired cellular organelle involved in this patient's condition?]]
Answer A	AnswerA::It is involved in the addition of O-oligosaccharides to serine and threonine residues
Answer A Explanation	AnswerAExp::The cellular organelle involved in I-cell disease disease is the Golgi apparatus, which normally modifies N-oligosaccharides on asparagine and adds O-oligosaccharides to serine and threonine residues.
Answer B	AnswerB::Modification of N-oligosaccharides on glycine
Answer B Explanation	AnswerBExp::Modification of N-oligosaccharides is on asparagine.
Answer C	AnswerC::It is involved in the addition of glucose -6-phosphate to proteins
Answer C Explanation	AnswerCExp::The Golgi apparatus is involved in the addition of mannose-6-phosphate to specific lysosomal proteins.
Answer D	AnswerD::It is a distribution center of proteins and lipids from the endoplasmic reticulum to the mitochondria
Answer D Explanation	AnswerDExp::The Golgi apparatus is a distribution center of proteins and lipids from the endoplasmic reticulum to the plasma membrane, lysosomes, and secretory vesicles.
Answer E	AnswerE::It is involved in proteoglycan assembly from prelysosomes
Answer E Explanation	AnswerEExp::The Golgi apparatus is involved in proteoglycan assembly from core proteins.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Inclusion cell disease (I-cell disease) is an inherited lysosomal storage disorder characterized by failure of addition of mannose -6- phosphate to lysosome proteins. It usually manifests with coarse facial features, clouded corneas, restricted joint movement, and in the majority of cases, it is fatal in childhood. The disease is caused by defective phosphotransferase enzyme that is located on the Golgi apparatus (involved cellular organelle). The Golgi apparatus is a distribution center of proteins and lipids from the endoplasmic reticulum (ER) to the plasma membrane, lysosomes, and secretory vesicles. It modifies N-oligosaccharides on asparagine and adds O-oligosaccharides to serine and threonine residues. Educational Objective: The cellular organelle involved in I-cell disease disease is the Golgi apparatus. It is a distribution center of proteins and lipids from the endoplasmic reticulum (ER) to the plasma membrane, lysosomes, and secretory vesicles. It modifies N-oligosaccharides on asparagine and adds O-oligosaccharides to serine and threonine residues. References: Leroy JG, DeMars RI, Opitz JM. I-cell disease; Birth Defects Orig Art Ser. 1969;4:174-85. First Aid 2015 page 73.]]
Approved	Approved::Yes
Keyword	WBRKeyword::I-cell disease, WBRKeyword::Golgi apparatus, WBRKeyword::Organelle, WBRKeyword::O-oligosaccharides, WBRKeyword::Serine, WBRKeyword::Threonine
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