Novel phenotypes observed in patients with -linked leukaemia/familial thrombocytopenia syndrome and a biallelic risk allele as leukaemogenic cofactor.

The phenotypes of patients with the recently discovered, dominant, -linked leukaemia predisposition and familial thrombocytopenia syndrome are variable, and the exact mechanism of leukaemogenesis remains unclear. Here, we present novel clinical and laboratory phenotypes of seven individuals from three families with germline mutations and a refined genetic analysis of one child with additional high-hyperdiploid acute lymphoblastic leukaemia (HD-ALL), aiming to elucidate second oncogenic hits. Four individuals from two pedigrees harboured one novel or one previously described variant in the central domain of (c.592C>T, p.Gln198* or c.641C>T, p.Pro241Leu, respectively). Neutropenia was an accompanying feature in one of these families that also harboured a variant in (c.1098_1103dup, p.Ile366_Gly367dup), while in the other, an autism-spectrum disorder was observed. In the third family, the index patient suffered from HD-ALL and life-threatening pulmonary mucor mycosis, and had a positive family history of 'immune' thrombocytopenia. Genetic analyses revealed a novel heterozygous mutation in the ETS domain of (c.1136T>C, p.Leu379Pro) along with absence of heterozygosity of chromosome (10)(q21.2q21.3), yielding a biallelic leukaemia risk allele in (rs7090445-C). The neutrophil function was normal in all individuals tested, and the platelet immune histochemistry of all three pedigrees showed delta-storage-pool defect-like features and cytoskeletal defects. Our clinical observations and results of high-resolution genetic analyses extend the spectrum of possible phenotypes cosegregating with germline mutations. Further, we propose as potential leukaemogenic cofactor in patients with -linked leukaemia predisposition and familial thrombocytopenia syndrome.