The familial platelet disorder with predisposition to acute myeloid leukemia (FPD/AML) is an autosomal dominant disorder characterized by germline RUNX1 alterations. Missense, nonsense and frameshift mutations as well as intragenic duplications and large deletions of RUNX1 (21q22) have been reported in less than 45 pedigrees. Transformation to acute leukemia (AL) occurs with an incomplete penetrance and at a variable age in FPD/AML patients, suggesting that germline RUNX1 mutations alone are insufficient to induce AL. Thus this disorder represents a unique model to study leukemic progression. RUNX1 mutation could be considered like an inherited ‘first hitL, leading to a preleukemic state, but additional genetic alterations are required for the formation of fully transformed leukemic cells. To date, the most frequent additional event implicates an acquired mutation in the second allele of RUNX1. 1 Despite this, recurrent mutations coinciding with transformation to AL are not yet well defined. Recently, somatic mutations in the cell cycle regulator CDC25C were identified in 53% of FPD/AML patients. CDC25C mutations appeared to occur in the preleukemic clone, and subsequent mutations in other genes, such as GATA2, coincided with leukemia progression. 2 Moreover, a number of somatic mutations have been recently described to significantly co-occur with somatic RUNX1 aberrations in AML, including mutations in the Polycomb-associated genes ASXL1/2 in t (8; 21) AML, as well as in RUNX1-mutated AML. 3 Intriguingly, an acquired ASXL1 mutation has been also described in a FPD/AML patient who developed T-ALL. 4 Given these recent discoveries and the lack of recurrent mutations known to coincide with leukemic progression of FPD/AML patients, we explored the status of 44 AML-associated genes in 25 individuals from 15 FPD/AML pedigrees. Interestingly, we identified a second alteration of RUNX1 in all patients who developed AML, in contrast to patients who developed T-ALL.

The FPD/AML patients were identified from 2005 to 2014 (Supplementary Material, Supplementary Figure S1A), and biological samples were collected after informed consent, in accordance with the Declaration of Helsinki. Genomic DNA was extracted from peripheral blood or bone marrow mononuclear cells, using standard procedures. Next-generation sequencing (NGS) was performed at thrombocytopenia stage if the patients