PRF1 and hemophagocytic syndrome: We are aware of only limited additional observations of fetal AID: a case of OS at birth due to an IL7Rα deficiency (10) and a few reports on fetal hydrops associated with HLH (hemophagocytic lymphohistiocytosis), including two perforin-deficient twins (11); these cases were described as non-immune hydrops but, as discussed above, we would classify them as AID due to innate immunity mechanisms.