FBN1 and Chronic Eosinophilic Leukemia, Not Otherwise Specified: In another study performed by Guo et al., the incidence of IEL in 127 patients diagnosed with CEL was 20.5% (26/127), the mutation frequency of the ADAMTSL4 gene in CEL and IEL cases was 3.94% (5/127) and 19.2% (5/26), respectively, while the frequency of FBN1 mutations in IEL cases was 57.7% (15/26) [12].