Biochemistry:

A term child is delivered by spontaneous vaginal delivery with no complications. On physical examination the child has restricted movement in shoulder and elbow joints, bilateral hip dislocations and coarse facial features. Laboratory studies show that the activities of β-hexosaminidase, iduronate sulfatase, and arylsulfatase A are 20 times normal in serum but are deficient in the cultured fibroblasts. This disease is associated with which of the following abnormal cellular components?

A- Apolipoprotein B-48
B- Collagen
C- Mannose-6-phosphate
D- Rough endoplasmic reticulum
E- Sphingomyelinase

 
[expand title=”CLICK HERE VIEW CORRECT ANSWER:”][sociallocker]The correct answer is C. I-cell disease is caused by a failure of addition of mannose-6-phosphate, an intracellular signal sequence, to lysosomal proteins, leading to an inappropriate release of those proteins into the extracellular space. Thus, lysosomal enzymes, including hexosaminidase, iduronate sulfatase, and arylsulfatase A, will be found in the extracellular space, but not intracellularly. I-cell disease is characterized by skeletal abnormalities, restricted joint movement, coarse facial features, and severe psychomotor impairment. Death usually occurs by the age of 8 years.[/sociallocker][/expand]