Answer and Discussion of Quiz Set: N-009

3.    Electron microscopy will not be helpful in identifying abnormal metabolites in which of the following diseases?

A.  Krabbe's disease

B.  Tay Sachs Disease

C.  X-linked adrenocortical leukodystrophy

D.  Mucopolysaccharides

E.  McArdle's disease

Answer and Discussion: The answer is (D). A substance has to be at least partially water insoluble in order for it to be detected under the electron microscope. Water insoluble lipid is accumulated in Krabbe's disease, Tay Sachs disease,  and X-linked adrenocortical leukodystrophy. Excessive glycogen is present in McArdle's disease. Glycogen is only partially soluble. Although some of the glycogen may be dissolved during processing, most of the glycogen often remains undisolved which will be able to be detected under electron microscopy. The abnormal accumulation of mucopolysaccharides is water soluble and therefore it will not be visualized under the electron microscope. The abnormal metabolite in Canavan disease is a water soluble organic acid and there is no accumulation. Electron microscopy will, therefore, not be able to identify this organic acid.