Abnormal salivary proteins in autism

A saliva test for autism spectrum disorder (ASD) is being developed by researchers in Italy. Their test involves a sophisticated mass spectrometric technique and associated statistical analysis of the data. It could provide researchers with a useful biomarker approach for a subgroup of ASD patients.

This month, a new book - Britain's Einstein - suggests that physics genius Paul Dirac may have been autistic and almost in response to its publication autism expert Simon Baron-Cohen of Cambridge University calls for a public debate on whether we should use antenatal screening for ASD. The social ramifications of such a test could be immense. Given a positive result and a subsequent abortion choice, might the test ultimately deprive the world of future geniuses or even people with the strong talents sometimes associated with some forms of ASD, such as unusual skill in mathematics?

Antenatal tests for autism are being developed in several labs using various approaches, but the Italian team's discovery of abnormal proteins in the saliva of people on the autistic spectrum could provide clues as to the molecular basis of ASD.

Massimo Castagnola, Rosanna Inzitari, Chiara Fanali, Alessandra Morelli, Anna Maria Pecoraro, and Maria Giulia Torrioli of Catholic University of Rome and Irene Messana and Tiziana Cabras of the University of Cagliari published details of their findings in the Journal of Proteome Research earlier this month.

Commonly, autism involves social withdrawal, impaired emotional responses and communication skills, and various other symptoms, including mental retardation in extreme cases. However, it is referred to as a spectral disorder with a wide range of degrees of symptoms displayed from very mild symptoms to those extremes. There is currently no laboratory test available to test for ASD.

"Genetic factors play a major role [in ASD] and include chromosomal abnormalities (in about 10% of patients) or mutations in single genes (probably less than 5%) involved in synaptic development," the researchers explain. "However, according to a general way of thinking, it has been proposed that a few strong acting genes or, alternatively, many weak genes work together to cause autism susceptibility." Given the complex genetics of ASD explaining the biochemical-biological causes of ASD and developing a test have remained a major research challenge.

Scientists have been searching for biomarkers, such as abnormal proteins, present in the bodily fluids of individuals with ASD for many years. The discovery of such a biomarker would provide the means to accurately diagnose ASD, allow support for patients and carers to be provided in a more effective and timely manner. It could also allow the patient's response to treatment to be monitored with greater precision.

With this in mind, the Italian researchers compared proteins found in the saliva of 27 children with ASD to those in a control group without a diagnosis of ASD. They used reversed-phase high performance liquid chromatography (RP-HPLC) to separate the proteins found in the samples and electrospray ionization mass spectrometry (ESI-MS) to identify the components.

They found that at least one of four protein fragments, the salivary peptides statherin, histatin 1 and acidic proline-rich proteins, in 19 of the children from the ASD group had significantly lower levels of phosphorylation. Phosphorylation is a key biochemical process that activates proteins. "Phosphorylation of salivary peptides involves a Golgi casein kinase [enzyme] common to many organs and tissues, CNS included, whose expression seems to be synchronized during foetal development," the researchers explain.

The team also found that 10 of the children with normal or borderline development also presented "hypo-phosphorylated" salivary peptides. This, the researchers suggest, may indicate that the anomaly could relate mainly to the behavioural aspects of ASD rather than overall mental and physical development.

The Italian results suggest that these abnormal proteins might be indicative of anomalies in the timing of phosphorylation of proteins involved in the development of the central nervous system in early infancy that are thought to be involved in ASD. However, the reduced phosphorylation might also be associated with other pathological conditions rather than ASD.

The team add that while their results are striking, there are limitations to their statistical analysis, given the limited number of patients tested. Additional work is now needed to develop a robust clinical test based on the work and to tease apart the causes from the effects in hypophosphorylation of salivary peptides and how they might relate to ASD if at all.