SLC14A1 and fetal erythroblastosis: They are products of twocodominant alleles (Jka and Jkb) of the SLC14A1 gene.(22) The Jk null (a-b-) phenotype leads to theproduction of anti-Jk3 antibodies and, although very rare in most populations,can cause alloimmunization.(3,20) Although there are reports offatal disease from anti-Jk3, such severity is an uncommon outcome, with mostcases, although rare, being mild.(20) Similarly, anti-Jka and anti-Jkb antibodies against theJk1 and Jk2 antigens respectively also cause mild HDFN.(9)