Abstract: There is disclosed the cloning and identification of human IL-23R splice variants caused by alternative splicing of the IL-23R mRNA in human. Alternative mRNA forms occur through skipping one, multiple full exons or partial exons, within the IL-23R gene. A total of twenty-five (25) different IL-23R transcripts were identified. A novel exon deletion (exon 9) isoform in the interleukin 23 receptor is disclosed, denoted as ?9. The present application also describes a quantitative assay to measure different IL-23R isoform. Detection of ?9 isoform of IL-23R is predominantly present in colon and cervical tissues. A decrease in ?9 is observed in inflamed colon tissues in Crohn's patients. There is disclosed a method of predicting Crohn's disease by measuring ?9 isoform of IL-23R.