My grandson has sickle cell disease and his mother has the D gene, but the father has normal hemoglobin.... all the paperwork from St Jude said there was a disconnect and his hemoglobin is normal? How is that possible, unless he’s not the father?

Mgt. I would suggest that they be re-tested.' If one parent has hemoglobin D trait and his father has sickle cell trait, there is a 25 percent (1 in 4) chance with each pregnancy of having a child with sickle cell (SD) disease.'
His father may have Sickle trait without symptoms.
Do I understand? If Junior has true sickle-cell disease and Dad is not a carrier, he is very unlikely to be the father. Hemoglobin "D" is a different inherited gene for a hemoglobin chain. It's time to talk with the physicians who are caring for him at Saint Jude. Nonpaternity happens and now that the question has been raised, it will not go away. Dad may still love Junior and Mom.