ORLANDO – Children with chronic immune thrombocytopenia (ITP) have an increased frequency of damaging variants in genes associated with cellular immunity, notably IFNA17 and IFNLR1, based on the results of whole genome sequencing.
The links to IFNA17 and IFNLR1 genes, which are involved in T cell pathways, remain significant when patients are stratified according to disease severity, Dr. Jenny M. Despotovic reported at the annual meeting of the American Sociey of Hematology. The finding is further evidence for the role of T cell abnormalities in the pathophysiology of chronic ITP.
Dr. Jenny M. Despotovic
These may be important candidate genes involved in immune regulation and in sustained autoimmunity, which appears to be due to generalized immune dysregulation that includes altered T cell balance with a shift toward immune activation (increased Th1/Th2 ratio) as well as decreased number and impaired function of regulatory T cells, said Dr. Despotovic, of Texas Children’s Cancer and Hematology Centers, Baylor College of Medicine, Houston.
In their study, Dr. Despotovic and her colleagues performed whole exome sequencing on 262 samples with robust phenotype data from children with chronic ITP in the North American Chronic ITP Registry and the Platelet Disorders Center at the Weill-Cornell Medical Center. All but three patients were less than 20 years old at diagnosis; 83% had primary ITP, 10% had Evans syndrome, and 7% had other autoimmune disorders.
To identify candidate genes associated with ITP susceptibility, sequencing data were compared for 172 ITP cases of European American ancestry and 5,664 controls of European American ancestry with platelet levels over 150 x 109/L in the Atherosclerosis Risk in Communities (ARIC) Study. In a separate analysis, phenotype data for ITP cases were reviewed and cases were stratified by disease severity according to the need for second line treatment.
A significant increase in the frequency of several damaging variants were identified in genes in the ITP cohort. The most significant associations were detected in the IFNA17 gene, which is involved in transforming growth factor beta secretion and could affect number and function of regulatory T cells.
IFNA17 rs9298814 was identified in 26% of cases in the ITP cohort compared to less than 0.01% of controls. In all, 43% of ITP patients had at a presumed deleterious variant of IFNA17.
IFNA17 gene variants remained significant in the most severely affected patients, specifically those requiring second line therapy, providing further evidence for this gene’s functional relevance in the pathogenesis and pathophysiology of ITP, Dr. Despotovic said.
Other genes with known impact on T cell number or function, including DGCR14, SMAD2 and CD83 also contained an increased frequency of variants in the European American ITP cohort. IFNLR1 and REL genes were also significantly associated with need for second line ITP therapy.
Analysis of this large cohort did not validate any of over 20 variants that have been previously published as candidates for ITP susceptibility or evolution to chronic ITP, she added.
On Twitter @maryjodales