Hi,
First time poster here, long time lurker, germline RUNX1-mutant myself. Father got AML, three decades of thrombocypenia for me, child is mutant as well, no event fortunately but under surveillance. Good news for your child!
Fortunately only his cancer was RUNX1, not his whole genome. It was also trisomy-21. Essentially he had what his doc described as the "stereotypical" B-ALL for individuals with Down Syndrome, but he doesn't have it.