Whole exome sequencing reveals a C-terminal germline variant in CEBPA-associated acute myeloid leukemia: 45-year follow up of a large family

Abstract

F amilial acute myeloid leukemia is rare and linked to germline mutations in RUNX1, GATA2 or CCAAT/enhancer binding protein-a (CEBPA). We re-evaluated a large family with acute myeloid leukemia originally seen at NIH in 1969. We used whole exome sequencing to study this family, and conducted in silico bioinformatics analysis, protein structural modeling and laboratory experiments to assess the impact of the identified CEBPA Q311P mutation. Unlike most previously identified germline mutations in CEBPA, which were N-terminal frameshift mutations, we identified a novel Q311P variant that was located in the C-terminal bZip domain of C/EBPa. Protein structural modeling suggested that the Q311P mutation alters the ability of the CEBPA dimer to bind DNA. Electrophoretic mobility shift assays showed that the Q311P mu-tant had attenuated binding to DNA, as predicted by the protein modeling. Consistent with these findings, we found that the Q311P mutation has reduced transactivation, consistent with a loss-of-function mutation. From 45 years of follow up, we observed incomplete penetrance (46%) of CEBPA Q311P. This study of a large multi-generational pedigree reveals that a germline mutation in the C-terminal bZip domain can alter the ability of C/EBP-a to bind DNA and reduces transactivation, leading to acute myeloid leukemia.

Transcription factor mutations as a cause of familial myeloid neoplasms

“…Germline upstream frameshift versus leucine zipper missense mutations appear to differ in expected penetrance, highlighting differences in biologic mechanisms. Whereas approximately 100% of those carrying an upstream frameshift are expected to develop AML, a lower proportion of those with distal leucine zipper mutations develop AML (estimated at 45%) (171,176). These differences closely parallel findings in model systems.…”

“…Among germline cases at the time of AML development and AML cases with acquired biallelic mutations, nearly all cases have acquired a second CEBPA mutation on the previously normal allele, commonly disrupting the C/EBPα C-terminal leucine zipper. Rare families with germline missense mutations disrupting the leucine zipper have been reported (175,176).…”

Genomic approaches to accelerate cancer interception

“…Nearly 30 novel susceptibility genes have been identified using various forms of DNA sequencing in the last five years. Some of these novel genes are listed in Table 2 18–24 while others were summarized in a previous review 25 . Examples include variants in the POLE gene in colorectal cancer 26 or variants in the promoter region of TERT in familial and sporadic melanoma 27 .…”

Recommendations for Surveillance for Children with Leukemia-Predisposing Conditions

“…Familial AML due to germline mutations in CEBPA, the gene encoding a key transcription factor involved in the development of granulocytes from common myeloid progenitors (45,46), is an autosomal dominant condition in which AML typically occurs earlier and more frequently than is the case in sporadic AML. At least 45% of individuals with germline CEBPA mutations develop AML, most commonly in the third decade, but onset has been reported as early as the first few years of life (47,48). Approximately 5% to 14% of all AML patients have monoallelic or biallelic somatic CEBPA mutations in their leukemic cells.…”

“…Leukemias developing in the context of CEBPA-associated predisposition to AML usually show acquisition of somatic mutations affecting the 3 0 end of the remaining CEBPA allele (47). Rarely, 3 0 end CEBPA mutations have been reported as germline events in families exhibiting incomplete leukemia penetrance (48). Individuals with germline CEBPA mutations tolerate AML therapy, and long remissions can be induced.…”