11/30/2021 Dr. Minji Byun’s research team at Mount Sinai has been actively investigating genetic factors for susceptibility to idiopathic multicentric Castleman disease (iMCD) ever since she received a grant from the Castleman Disease Collaborative Network and Penn Orphan Disease Center in 2016. In their recent study published in the Journal of Experimental Medicine, they reported a teenage iMCD patient who had a large portion of his blood cells harboring a unique acquired mutation in the gene DNMT3A.
DNMT3A encodes an enzyme that carries out de novo DNA methylation, which is essential for the acquisition of cellular identity and specialized functions during cellular differentiation. DNMT3A is the most frequently mutated gene in age-related clonal hematopoiesis. As such, mature immune cells harboring DNMT3A mutations can be readily detected in elderly persons. Most DNMT3A mutations associated with clonal hematopoiesis are heterozygous and predicted to cause loss of function, indicating that haploinsufficiency is the predominant pathogenic mechanism. Yet, the impact of DNMT3A haploinsufficiency on the function of mature immune cells is poorly understood. Here, we demonstrate that DNMT3A haploinsufficiency impairs the gain of DNA methylation at decommissioned enhancers, while simultaneously and unexpectedly impairing DNA demethylation of newly activated enhancers in mature human myeloid cells. The DNA methylation defects alter the activity of affected enhancers, leading to abnormal gene expression and impaired immune response. These findings provide insights into the mechanism of immune dysfunction associated with clonal hematopoiesis and acquired DNMT3A mutations.