To evaluate the presence of serum protein biomarkers associated with the early 
phases of formation of carotid atherosclerotic plaques, label-free quantitative 
proteomics analyses were made for serum samples collected as part of The 
Cardiovascular Risk in Young Finns Study. Samples from subjects who had an 
asymptomatic carotid artery plaque detected by ultrasound examination (N = 43, 
Age = 30-45 years) were compared with plaque free controls (N = 43) (matched for 
age, sex, body weight and systolic blood pressure). Seven proteins (p < 0.05) 
that have been previously linked with atherosclerotic phenotypes were 
differentially abundant. Fibulin 1 proteoform C (FBLN1C), 
Beta-ala-his-dipeptidase (CNDP1), Cadherin-13 (CDH13), Gelsolin (GSN) and 72 kDa 
type IV collagenase (MMP2) were less abundant in cases, whereas Apolipoproteins 
C-III (APOC3) and apolipoprotein E (APOE) were more abundant. Using machine 
learning analysis, a biomarker panel of FBLN1C, APOE and CDH13 was identified, 
which classified cases from controls with an area under receiver-operating 
characteristic curve (AUROC) value of 0.79. Furthermore, using selected reaction 
monitoring mass spectrometry (SRM-MS) the decreased abundance of FBLN1C was 
verified. In relation to previous associations of FBLN1C with atherosclerotic 
lesions, the observation could reflect its involvement in the initiation of the 
plaque formation, or represent a particular risk phenotype.