Autism spectrum disorders (ASDs) are neurodevelopmental and behavioural syndromes affecting social orientation, behaviour, and communication that can be classified as developmental disorders. ASD is also associated with immune system abnormality. Immune system abnormalities may be caused partly by complement system factor I deficiency. Complement factor I is a serine protease present in human plasma that is involved in the degradation of complement protein C3b, which is a major opsonin of the complement system. Deficiency in factor I activity is associated with an increased incidence of infections in humans. In this paper, we show that the mean level of factor I activity in the ASD group is significantly higher than in the control group of typically developed and healthy children, suggesting that high activity of complement factor I might have an impact on the development of ASD.

Autism Spectrum Disorders (ASD) are classified as neurological developmental disorders. Several studies have been carried out to find a candidate biomarker linked to development of these disorders, but up to date no reliable biomarker is available. Mass spectrometry techniques have been used for protein profiling of blood plasma of children with such disorders in order to identify proteins/peptides which may be used as biomarkers for detection of the disorders. Three differentially expressed peptides with mass charged (m/z) values of 2,020 ± 1, 1,864 ± 1, and 1,978 ± 1 Da in heparin plasma of children with ASD which were significantly changed as compared to the peptide pattern of the non-ASD control group are reported here. This novel set of biomarkers allows for a reliable blood based diagnostic tool that may be used in diagnosis and potentially, in prognosis of ASD.