Five New Pedigrees with Inherited RUNX1 Mutations Causing Familial Platelet Disorder with Propensity to Myeloid Malignancy (FPD/AML)

Familial platelet disorder with propensity to myeloid malignancy (FPD/AML) is an autosomal dominant syndrome characterised by platelet abnormalities and a predisposition to myelodysplasia (MDS) and/or acute myeloid leukemia (AML). The disorder, caused by inherited mutations in RUNX1, is uncommon with only 14 pedigrees reported. We screened 10 families with a history of more than one first- degree relative with MDS/AML and detected inherited mutations in RUNX1 in 5 of these pedigrees. Several affected members had normal platelet counts or platelet function, features not previously reported in FPD/AML. The median incidence of MDS/AML among carriers of RUNX1 mutation was 35%. Individual treatments varied but included hematopoietic stem cell transplantation (HSCT) from siblings before recognition of the inherited leukemogenic mutation. Transplantation was associated with a high incidence of complications including early relapse, failure of engraftment and post-transplantation lymphoproliferative disorder. As acquired trisomy 13 and 21 and FLT3-ITD have all been associated with RUNX1 mutation in sporadic MDS/AML, a combination of single nucleotide polymorphism profiling and mutation analysis was performed to determine whether these secondary genetic events were implicated in the onset of overt malignancy in FPD/AML. Five disease (MDS and/or AML) samples from 4 of our pedigrees with FPD/AML were screened and in all cases, these abnormalities were excluded. Therefore, the secondary mutations that promote MDS/AML in individuals with germline RUNX1 mutations are distinct from those reported in sporadic cases and require further investigation. The small size of modern families and the clinical heterogeneity of the FPD/AML syndrome may have resulted in the diagnosis being previously overlooked. Based on our data, FPD/AML may be more prevalent than previously recognized and therefore, it would appear prudent to screen young patients with MDS/AML for RUNX1 mutation, particularly prior to consideration of sibling HSCT.