Glycosylation is an integral part in health and disease, as emphasized by the 
growing number of identified glycosylation defects. In humans, proteins are 
modified with a diverse range of glycoforms synthesized in complex biosynthetic 
pathways. Glycosylation disorders have been described in congenital disorders of 
glycosylation (CDG) as well as in acquired disease conditions such and 
non-alcoholic fatty liver disease (NAFLD). A hallmark in a subset of CDG cases 
is the reduced glycosylation site occupancy of asparagine-linked glycans. Using 
an optimized method protocol, we determined the glycosylation site occupancy 
from four proteins of hepatic and lymphatic origin from CDG and NAFLD patients. 
We found variable degrees of site occupancy, depending on the tissue of origin 
and the disease condition. In CDG glycosylation sites of IgG2 and IgA1 were 
occupied to normal levels. In NAFLD haptoglobin and transferrin glycosylation 
sites were hyper-glycosylated, a property qualifying for its use as a potential 
biomarker. Furthermore, we observed, that glycosylation sites of 
liver-originating transferrin and haptoglobin are differentially occupied under 
physiological conditions, a further instance not noticed in serum proteins to 
date. Our findings suggest the use of serum protein hyperglycosylation as a 
biomarker for early stages of NAFLD.