Answer and Discussion of Quiz Set: N-009

4.    Abnormal accumulation of substances will be detected by electron microscopy in which of the following diseases?

A.  Canavan's disease

B.  Glutaric acidemia type I

C.  Methanol intoxication

D.  Hartnup disease

E.  Gangliosidosis (GM1 and GM2)

Answer and Discussion: The answer is (E). With the same token in quez #3 of this set, gangliosidosis lead to insoluble accumulation of water insoluble lipids and therefore it can be identified under electronscope. The abnormal metabolite in Canavan disease N-acetylaspartic acidN-acetylaspartic acid which is water soluble. Hartnup disease is biochemically characterized by defective transport of neutral amino acids (including tryptophan) across the intestine and kidney. Glutaric aciduria is resulted from failure in completely breaking down lysine, hydroxylysine and tryptophan. Excessive accumulation of of their intermediate breakdown products (glutaric acid, glutaryl-CoA, 3-hydroxyglutaric acid, glutaconic acid) is toxic and damages the brain particularly the basal ganglia. Since the abnormal metabolites of these three diseases are highly water soluble, it will not be identified by electron microscopy. Methanol will be oxidized to methanal (formaldehyde) and then to formic acid in the human body. Both of these products are extremely toxic but also soluble and cannot be accumulate. Methanol can also cause depression of the central nervous system in the same manner as ethanol.