Blood Group: Kell
Common: Approximately 100% Caucasians and 80% Blacks are Jsa- and at risk for developing anti-Jsa. 
Causes HDN: Yes
The first case of hydrops from anti-Jsa was reported in 2005. What is startling to note about this was that the mother's Indirect Coombs test was NEGATIVE despite the infant having hydrops and a positive direct coombs (strength of 3+). The woman had lost an infant before due to hydrops, the cause of which was never identified. Further testing revealed the woman to be Jsa- and the baby Jsa+. Both maternal and fetal blood reacted with Jsa+ cells and they were able to identify the antibody as anti-Jsa. Delayed onset anemia was found on day 14 and the infant was treated with a transfusion, phototherapy and erythropoietin. 
In addition to the red blood cells being hemolyzed, erythroid and myeloid precursors are inhibited. 
While Anti-Jsa does not always cause HDN require a transfusion , in some cases HDN due to anti-Jsa can cause anemia requiring a post birth transfusion.  Anti-Jsa can cause delayed onset anemia as well .