[Seetal]

A 2-year-old boy is brought into the clinic by his parents, who are concerned about his development. They state that his motor development (especially the range of motion of his joints) is delayed when compared to his older siblings, and that he is much smaller than other children his age. His face appears to have coarse features, and enlargement of the liver and spleen is noted. What function, which contributes to the pathophysiology of this disease, is compromised?

A. Assembly of ribosomes
B. Degradation of proteins
C. Glycosylation of newly synthesized proteins
D. Transcription of RNA
E. Translation of peptide chains

 

[drmodi44]

I cell Disease....
defect in co translation modification....phosphorylation...
E. Translation of peptide chains ....

 

[Seetal]

u got the disease right but unfortunately the answer wrong. i faced this many times when answering questions on various qbanks. i get so frustrated though. think again kushboo, ull get the answer. ill post it soon with the explanation.

 

[drmodi44]

C. Glycosylation of newly synthesized proteins

 

[step1an]

C. Glycosylation of newly synthesized proteins

 

[Seetal]

yes! and this is why..

Option C (Glycosylation of newly synthesized proteins) is correct.

The patient has I cell disease (mucolipidosis type II), which results from a deficient process in the Golgi complex. The exact deficiency is with the N-acetylglucosamine 1-phosphotransferase enzyme, which starts the process of adding a mannose-6-phosphate residue to enzymes that are destined for the lysosome. Without mannose-6-phosphate, the enzymes are sent outside the cell. This pathophysiology is seen in I cell disease, and the lack of digestive enzymes in the lysosome results in accumulation of undigested products in intracellular inclusion bodies (hence the term "I" for inclusion).

 

[drmodi44]

Is not it phosphorylation that is defective?
I thought glycolysation must be diiferent thing

 

[Seetal]

Is not it phosphorylation that is defective?
I thought glycolysation must be diiferent thing

yeah.. i always related glycolysation with Hb in DM due to increased glucose, where the excess glucose is now bound to the erythrocytes forming Hb1AC.

 

[drmodi44]

its mannose 6 phosphate that is not being incorporated....
mannose = glucose = Glycosylation
6-phosphate = phosphorylation....
now won't confuse it...:redcheeks;

 

[step1an]

Is not it phosphorylation that is defective?
I thought glycolysation must be diiferent thing

All the newly synthesized proteins by a cell which need to be excreted, transported to the cell membrane or transported to lysosomes undergo glycosylation.

Now among these glycosylated proteins, the proteins which have to reach lysosome undergo phosphorylation of their mannose residues.

So the specific defect in I-cell disease is defective phosphorylation but as this is not given in the option. The next closest option is defective glycosylation.