In the field of diseases related to glycosylation disorders, congenital defects associated with abnormalities in both O- and N-glycosylation of proteins constitute arising novel entities. Defects in subunits of the conserved oligomeric Golgi protein complex have been shown to be involved in an important part of previously unsolved CDG type II combining abnormalities in both mucin type core1 O- and N-glycans; furthermore, recent studies revealed that autosomal recessive cutis laxa type II could also be associated with such combined glycosylation defects. Based on the studies of serum samples from three patients including a case of cutis laxa, we present here evidence that 2-DE of apolipoprotein C-III in combination with MALDI-TOF-MS analysis of serum O- and N-glycans allow the detection and the biochemical characterization of these newly recognized glycosylation disorders.