“…25,26,[29][30][31] In contrast, the incidence of acute GVHD in children with high-risk SCD who received BMTs from HLA-identical sibs ranges from 18-38% but is mostly mild to moderate (grades I and II). 14,15,18,19 The incidence of extensive chronic GVHD in children undergoing UPBCT (9%) 31 is similar to that reported after BMT from HLA-identical sibs for high-risk SCD (3-8%). 13,14,15,18,19 The degree of HLA disparity (greater than one antigen difference between donor and recipient vs zero to one antigen difference) has been suggested as a risk factor for development of GVHD, 26 but other studies have not confirmed this observation.…”