Transient epileptic amnesia--a clinical update and a reformulation.

Abstract

<h3>Abstract</h3> The super-enhancers (SE) of lineage-specific genes in B-cells are off-target sites of somatic hypermutation. However, the inability to detect sufficient numbers of mutations in normal human B-cells has precluded the generation of a high-resolution mutational landscape of SEs. Here, we captured and sequenced 12 B-cell SEs at single-nucleotide resolution from ten healthy individuals across diverse ethnicities. We detected a total of ∼9000 subclonal mutations (allele frequencies &lt;0.1%); of these, ∼8000 are present in the <i>BCL6</i> SE alone. Within the <i>BCL6</i> SE, we identified three regions of clustered mutations where the mutation frequency is ∼7X10^-4. Mutational spectra show a predominance of C&gt;T/G&gt;A and A&gt;G/T&gt;C substitutions, consistent with the activities of activation-induced-cytidine deaminase (AID) and the A-T mutator, DNA Polymerase η, respectively, in mutagenesis in normal B-cells. Analyses of mutational signatures further corroborate the participation of these factors in this process. Single base substitution signature SBS85, SBS37, and SBS39 were found in the <i>BCL6</i> SE. While SBS85 is a denoted signature of AID in lymphoid cells, the etiologies of SBS37 and SBS39 are still unknown. Our analysis suggests the contribution of error-prone DNA polymerases to the latter signatures. The high-resolution mutation landscape has enabled accurate profiling of subclonal mutations in B-cell SEs in normal individuals. By virtue of the fact that subclonal SE mutations are clonally expanded in B-cell lymphomas, our studies also offer the potential for early detection of neoplastic alterations. <h3>Significance</h3> We used Duplex Sequencing to detect low-frequency mutations in the <i>BCL6</i> super-enhancer locus in normal human B-cells. The landscape of pre-existing mutations is remarkably conserved across different ethnicities and reveals clustered mutational hotspots that correlate with reported sites of clonal mutations and translocation breakpoints in human B-cell lymphomas. This high-resolution genomic landscape revealed by Duplex Sequencing offers accurate and thorough profiling of low frequency, pre-existing mutations in normal individuals, and the potential for early detection of neoplastic alterations.