Figure 3.

Mathematical calculations and previously identified cMoMa cases

(A) Probability calculation for model 1 (two independent de novo 1-bp deletions on the same paternal allele during early embryogenesis) using a Poisson near-pair model. Assuming 12 daughter cells, 28.8 SNVs per cell division, an indel/SNV ratio of 1:13.78, and a 1-bp deletion fraction of 33.8%, the expected probability of two independent deletions occurring within ±3 bp on the same allele is ≤2.3 × 10⁻¹⁰ (D2–D3 window) and <10⁻⁷ even under permissive assumptions, effectively rejecting model 1.

(B) Systematic screening of MosaicBase (4,647 postzygotic mosaic variant entries) for haplotype-resolved cMoMa-like cases. Filtering for ≥2 variants in the same gene within ≤20 bp on the same phased allele identified two cases; WAS (homopolymer tract) and ACVRL1 (GC-rich secondary structure context).

(C) Combined, this gives a total of four reports (five affected individuals) with the specific cMoMa genotype: one from this study (HNRNPU variants), two from MosaicBase (WAS and ACVRL1 variants), and one additional case that we were able to identify in the literature (AHDC1 variants).