Extracellular Signal Related Kinase Activation in Autistic Disorder

Background:  Limited pathophysiological understanding of autistic disorder has plagued treatment development efforts in the field. Extracellular signal related kinase (ERK1/2) is a subfamily of mitogen-activated protein (MAP) kinases that mediate transmission of signals from cell surface receptors to cytoplasmic and nuclear effectors. Direct and indirect evidence from mouse and human models points to potential ERK1/2 dysregulation as a potential molecular marker of autistic disorder pathophysiology. ERK1/2 activation (phosphorylation) is an index of overall cellular activity.  Lymphocytic ERK1/2 activation has been shown to be dysregulated and correlate with brain ERK1/2 dysregulation in humans with and animal models of fragile X syndrome (FXS), a common single gene cause of autism. Taking steps to assess ERK1/2 activation in the pathophysiology of idiopathic autistic disorder will open up new targeted treatment opportunities focused on this potential marker of molecular dysregulation.

Objectives: We sought to evaluate peripheral lymphocytic ERK1/2 activation in an initial group of youth with idiopathic autistic disorder compared to age- and gender-matched neurotypical peers. We hypothesize that lymphocytic ERK1/2 activation will be increased in youth with ASD compared to control subjects consistent with preclinical findings of enhanced ERK1/2 activation in murine models of ASD.

Methods: We enrolled as many subjects as possible into this study (enrollment period January-June 2012) of lymphocytic ERK1/2 activation in youth with autistic disorder compared to matched neurotypical peers. Diagnostic criteria from the Diagnostic and Statistical Manual for Mental Disorders, 4^thEdition, Text Revision (DSM-IV-TR) were utilized. All subjects with autistic disorder met strict criteria for autistic disorder based on a score of greater than 13 on the Social Communication Questionnaire (SCQ) combined with a clinical interview using DSM-IV-TR autistic disorder criteria conducted by a physician with extensive experience in ASD diagnostics and research. All subjects, those with autistic disorder and controls, completed the SCQ and full medical and developmental histories. Additionally, subjects with autistic disorder completed the Aberrant Behavior Checklist (ABC), cognitive testing, and the Social Responsiveness Scale (SRS). To study peripheral lymphocytic ERK1/2 activation, lymphocytes from patients’ blood were collected, washed, counted, fixed in formaldehyde, and stained with phospho-ERK1/2 anti-body. ERK1/2 activation was reported as the percentage of ERK1/2 positive staining cells, minimum of 200 cells counted.

Results: 36 youth with autistic disorder and 19 youth with neurotypical development were enrolled (see Table 1; Subject Characteristics). Mean ERK1/2 activation was significantly increased in the samples from the youth with autistic disorder compared to controls (6.2 ± 4.0% versus 2.8 ± 2.1%; p=0.001).  A receiver operating curve (ROC) analysis looking at ERK1/2 activation and diagnosis had an area under the curve of 0.792 (p<0.0001) showing a significant association between ERK1/2 activation and diagnosis of autistic disorder in our sample. Future analysis will include correlation assessments of ERK1/2 activation and results from the ABC, SRS, and cognitive testing.

Conclusions: Peripheral ERK1/2 holds promise as a potential marker of molecular dysregulation in youth with autistic disorder. Future larger-scale study is warranted to study ERK1/2 activation in autism.