Elevated Vanin1 and Advillin Expression Is Associated with Progression to Chronic ITP in Children

The majority of pediatric ITP patients recover spontaneously within 6 months (acute ITP), while about 20% of the patients develop chronic ITP. The ability to distinguish patients at higher risk of developing chronic disease during the acute phase of the illness could give prognostic information and serve as a basis for clinical trials to study earlier or more aggressive interventions to prevent morbidity associated with long-term immunosuppression. We have previously described the gene expression pattern of pediatric ITP patients. This data set was used to search for genes which would predict progression to chronic ITP. We identified 8 samples from patients with acute self-limited ITP and 4 samples from patients who progressed to chronic ITP, all tested during the acute phase of the disease. At a false discovery rate of 0, two genes—VNN1 (vanin1) and AVIL (advillin) were the most significantly different between the groups. To validate these findings from microarray analysis, real-time PCR experiments were performed using unamplified whole blood RNA from the original cohort, with 4 additional patients (for a total of 9 samples in self-limited acute ITP group and 7 samples in progressed to chronic ITP group), and a control group of 5 normal children. All real-time data was normalized to housekeeping gene (GADPH) expression. Both VNN1 and AVIL expression were significantly increased in the group which developed chronic ITP compared to patients with acute self-limited ITP (VNN1 p=0.008, AVIL p=0.006) and normal controls (VNN1 p=0.044, AVIL p=0.009). Table 1 shows the medians and ranges of the normalized real-time PCR results of the three groups. The mechanism of these over-expressed genes in pediatric ITP patients who progress to chronic ITP is currently being investigated. VNN1 is a GPI anchored protein involved in T cell trafficking and has a pro-inflammatory role as an oxidative-stress response gene. AVIL, whose gene product is a member of the gelsolin/villin family of actin regulatory proteins, is involved in monocyte/macrophage phagocytosis and cytoskeletal remodeling. Thus both of these genes have functions consistent with recent reports implicating T cell regulation and trafficking as well as immune-mediated destruction of platelets in chronic ITP. These findings represent the first candidate biomarkers in predicting prognosis in pediatric ITP and at the same time open the door for further investigation of the molecular mechanism underlying the clinical transition from acute to chronic ITP. A prospective study to validate these findings is in progress.

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