The Molecular Investigation of Familial Leukaemia

Abstract

Acute myeloid leukaemia (AML) and myelodysplastic syndrome (MDS) are clonal disorders of haematopoiesis which culminate in bone marrow failure. In rare cases, families demonstrate an autosomal dominant predisposition to these disorders, associated with germline mutations in the haematopoietic transcription factors RUNX1, CEBPA, GATA2 and ETV6. This thesis investigates the molecular profiling of tumours from multiple families with different germline mutations, examining longitudinal patterns of disease evolution and identifying novel candidate germline lesions. Studies initially focused on the comprehensive characterisation of AML associated with germline CEBPA mutations. In-depth molecular profiling was performed to detail both the genetic events initiating leukaemia and the clinical progression of disease across multiple families. Integrated whole-exome (WES) and deep sequencing analysis revealed the presentation of entirely new leukaemic episodes initiating disease recurrence. This represents a unique model of disease progression in AML and clinical data support this hypothesis by demonstrating continued sensitivity to secondary therapies, with some patients experiencing several episodes of AML recurrence over decades. Convergence of tumour profiles was demonstrated across relatives from two families with different germline CEBPA mutations. To further explore this phenomenon, tumours from multiple siblings within a RUNX1-mutated family were investigated with WES. Three of the four siblings presented in an identical manner, all developing high risk MDS or secondary AML at 5 years of age. The molecular disease profiles were remarkable, as these 3 siblings all demonstrated somatic mutations causing upregulation of JAK-STAT signalling. This pattern of intra-familial disease convergence has not previously been reported in haematopoietic or solid familial tumours and highlights the importance of host genetic factors in governing somatic mutation acquisition. The final chapter of this thesis describes the investigation of novel germline lesions including partial allelic deletions of RUNX1 and atypical CEBPA and GATA2 mutations, with clinical manifestations varying significantly within these families. Novel genetic candidates are also discussed, highlighting the need for further work to demonstrate recurrence of these lesions. To conclude, this work reveals novel insights into the heterogeneous entity of familial leukaemia. By revealing unique patterns of disease evolution and intra-familial tumour convergence, these studies highlight the distinct properties of germline mutations in governing the biology of familial leukaemia. Further work is required to characterise the somatic and constitutional molecular landscape and determine the precise mechanisms governing disease latency, penetrance and phenotype.