Hematopoietic neoplasms with FGFR1 rearrangements are rare. Clinically, patients often present with a chronic myeloproliferative neoplasm with eosinophilia and an increased risk of transformation to acute leukemia. We report a patient who initially presented with B-cell acute lymphoblastic leukemia (B-ALL) with t(8;22)(p11.2;q11.2) and an additional derivative chromosome 22 [der(22)t(8;22)]. After induction chemotherapy, B-ALL blasts were eradicated; however, a chronic myeloproliferative process emerged showing persistent t(8;22) (p11.2;q11.2) but not der(22)t(8;22). Combined morphologic and fluorescence in situ hybridization revealed that both lymphoblasts and myeloid cells harbored t(8;22)(p11.2;q11.2); but only lymphoblasts carried the additional der(22)t(8;22). This case provides direct evidence to illustrate the clonal relationship of chronic phase and blast phase in myeloid neoplasms with FGFR1 rearrangement, and demonstrates that clonal cytogenetic evolution plays an important role in disease progression.
KIF1A is a molecular motor for membrane-bound cargo important to the development and survival of sensory neurons. KIF1A dysfunction has been associated with several Mendelian disorders with a spectrum of overlapping phenotypes, ranging from spastic paraplegia to intellectual disability. We present a novel pathogenic inframe deletion in the KIF1A molecular motor domain inherited by two affected siblings from an unaffected mother with apparent germline mosaicism. We identified eight additional cases with heterozygous, pathogenic KIF1A variants ascertained from a local data lake. Our data provide evidence for the expansion of
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