Outcomes in Hematopoietic Stem Cell Transplantation for Congenital Amegakaryocytic Thrombocytopenia.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare, inherited bone marrow failure syndrome. Hematopoietic stem cell transplantation (HSCT) is considered a curative treatment option, but existing descriptions of patient and transplant characteristics and outcomes after related and unrelated donor HSCT are sparse. We describe outcomes after HSCT for congenital amegakaryocytic thrombocytopenia (CAMT; n = 86) from 2000 to 2018. We conducted an analysis of data collected by the Center for International Blood and Marrow Transplant Research on patients with CAMT receiving therapeutic allogeneic HSCT. The predominant donor type was HLA-matched or mismatched unrelated donors (n = 58, 67%). The remaining included HLA-matched sibling (n = 23, 27%) and HLA-mismatched relative (n = 5, 6%). The predominant graft types were bone marrow (n = 53, 62%) and cord blood (n = 25, 29%). The median age at transplantation was 3 years, with 82 of 86 patients being transplanted aged ≤10 years. The 5-year graft failure-free and overall survival were 83% (95% confidence interval [CI], 74-90) and 86% (95% CI, 78-93), respectively. An examination for risk factors confirmed mortality was higher after HLA-mismatched relative and mismatched unrelated donor HSCT compared to HLA-matched sibling and matched unrelated donor HSCT (hazard ratio 3.52, P = .04; 75% versus 93%). The 1-year incidence of graft failure was 19% after HLA-mismatched HSCT (n = 32) compared to 7% after HLA-matched HSCT (n = 54, P = .15). Day-100 grade II-IV acute graft-versus-host disease was 13%, 26%, and 30% after HLA-matched sibling, HLA-matched and mismatched unrelated donor HSCT. The 5-year incidence of chronic graft-versus-host disease was 33% with 24 of 28 patients having received grafts from HLA-matched (n = 13) and mismatched unrelated (n = 11) donors. Although HLA-matched donors are preferred, HLA-mismatched donors also extend survival for CAMT.