The nhsbt website DOES say this:
When a patient tests positive for one of these syndromes, in most cases there’s a 50% chance that their siblings and their children each have the same syndrome. One of their parents likely has it as well.
https://www.nhsbt.nhs.uk/research-and-development/rd-blog/how-bone-marrow-stem-cells-can-support-acute-myeloid-leukemia-to-escape-chemotherapy-treatment/