Approximately 35% of the human genome can be identified as sequence devoid of a selected-effect function, and not derived from transposable elements or repeated sequences. We provide evidence supporting a known origin for a fraction of this sequence. We show that: 1) highly degraded, but near full length, ribosomal DNA (rDNA) units, including both 45S and Intergenic Spacer (IGS), can be found at multiple sites in the human genome on chromosomes without rDNA arrays, 2) that these rDNA sequences have a propensity for being centromere proximal, and 3) that sequence at all human functional rDNA array ends is divergent from canonical rDNA to the point that it is pseudogenic. We also show that small sequence strings of rDNA (from 45S + IGS) can be found distributed throughout the genome and are identifiable as an “rDNA-like signal”, representing 0.26% of the q-arm of HSA21 and ∼2% of the total sequence of other regions tested. The size of sequence strings found in the rDNA-like signal intergrade into the size of sequence strings that make up the full-length degrading rDNA units found scattered throughout the genome. We conclude that the displaced and degrading rDNA sequences are likely of a similar origin but represent different stages in their evolution towards random sequence. Collectively, our data suggests that over vast evolutionary time, rDNA arrays contribute to the production of junk DNA. The concept that the production of rDNA pseudogenes is a by-product of concerted evolution represents a previously under-appreciated process; we demonstrate here its importance.
Acute myeloid leukemia with germline CEBPA mutation is a subtype of acute myeloid leukemia that is associated with a favorable prognosis. Most of the reported cases of acute myeloid leukemia with CEBPA germline variants involve a germline variant in the N-terminus and a somatic variant in the C-terminus. There are only a few reported cases where the CEBPA germline variant has been identi ed in the C-terminus and the somatic variant in the N-terminus. This case report and review of the literature illustrates that, although acute myeloid leukemia with CEBPA N-or C-terminal germline variants have certain similarities such as atypically young age at diagnosis, frequent relapse, and favourable overall prognosis, there are also signi cant differences such as lower life-time penetrance of acute myeloid leukemia and shorter time to relapse for germline C-terminal cases. These ndings add important information on the natural history and clinical outcomes of acute myeloid leukemia with germline CEBPA C-terminal variants and these ndings should be considered in the management of patients and their family members. there appear to be signi cant differences with a lower life-time penetrance of AML and shorter time to relapse for C-terminal cases that must be considered when managing patients with AML with a CEBPA C-terminal germline variant and counselling their family members.
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