Normal metabolism of nucleotide sugars is very important. Any malfunction in any contributing enzyme will lead to a certain disease  for example:
#Inclusion body myopathy: is a congenital disease resulted from altered function of UDP-GlcNAc epimerase .
#Macular corneal dystrophy: is a congenital disease resulted from malfunction of GlcNAc-6-sulfotransferase.
#Congenital disorder in α-1,3 mannosyl transferase will result in a variety of clinical symptoms, e.g. hypotonia, psychomotor retardation, liver fibrosis and various feeding problems.