Urine proteome analysis to evaluate protein biomarkers in children with autism.

Background: Autism is a complex developmental disability for which no specific diagnostic markers have been identified so far. The present study aimed to evaluate whether there is any abnormal protein(s) excreted in the urine of autistic children by proteome analysis which may act as diagnostic marker.

Methods: Urine proteome analysis was carried out in first void urine samples of autistic and normal children (n=30) in the age group of 4-12 years by 2D-PAGE followed by MALDI-TOF-MS analysis.

Results: Comparison of 2D-PAGE gels revealed that many urinary proteins are expressed differentially in autistic children. Total numbers of spots observed were 250 and 159 in autism and normal samples respectively, out of which 95 matches were observed. In addition, 3 spots of abnormally expressed peptides were selected, excised and analyzed. Peptide sequence with significant match score was for kininogen-1 (KNG-1)-50 (spot-1), IgG1 heavy chain variable region-35(spot-2) and mannan-binding lectin serine protease-2 isoform-2 precursor-45(spot-3). All the autistic children showed significant increase (p<0.001) in urinary kininogen level measured quantitatively by ELISA, when compared to normal children.

Conclusion: Increased urinary kininogen-1 level in all the autistic children and the possibility of this protein as a diagnostic marker need further investigation.