Clustered monoallelic mosaicism in twins suggests previously unrecognized path of mutagenesis.

From the abstract

We report monozygotic twins with HNRNPU-related neurodevelopmental disorder who harbor two closely spaced mosaic single-nucleotide deletions on the same allele (c.1463del [p.Pro488Glnfs∗13] and c.1466del [p.Lys489Argfs∗12]). The variants are mutually exclusive on individual DNA molecules and result in three distinct cellular lineages within each individual.