The non-canonical signaling of truncated GOF CXCR4 variants is well-characterized within the context of WHIM syndrome and Waldenström's macroglobulinemia, where the hyperfunctional phenotype of truncated CXCR4 results in sequestration of cells in BM niches (12, 33, 39, 41–44). This evidence concerns the gene CXCR4 and WHIM syndrome.