Blood Group: Junior
Common: Jr(a−) phenotypes are rare. It is mostly asians who are at risk for developing anti-Jra .
Causes HDN: Yes
Critical Titer: 1:16
The first case of fatal HDN from anti-Jra was reported in 2008. The authors of the case study recommend close monitoring of pregnant women with a high-titer anti-Jr(a), especially those with an incompatible transfusion history and/or multiple pregnancies. 
Most cases of HDN from anti-Jra are mild, but severe cases do occur [2, 8]. The DAT (Direct coombs) can be negative and the infant have anemia . Upon an indirect coombs, anti-Jra was found with a titer 1:8. The direct coombs can be negative, but baby still be affected because infants can have low Jra antigen density immediately postpartum (basically the antigens aren't fully developed and in large quantities at birth). [2, 8]
Anti-Jra can inhibit formation of new blood cells in addition to destroying the blood cells [2, 8]. This makes it harder for baby to recover from anemia. In addition to having RBC broken down, the body cannot make more.
Anti-Jra can be difficult to identify in the mother  and may cause HDN in the first affected pregnancy [4, 9]
Anti-Jra can be treated with IUTs and may not cause hyperbilirubinemia (jaundice) 
1 - https://www.ncbi.nlm.nih.gov/pubmed/18522708
2 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4546206/
3 - https://www.ncbi.nlm.nih.gov/pubmed/14962310
4 - https://www.ncbi.nlm.nih.gov/pubmed/20890084
5 - https://www.ncbi.nlm.nih.gov/pubmed/16601336
6 - https://www.ncbi.nlm.nih.gov/pubmed/567888
7 - http://onlinelibrary.wiley.com/doi/10.1111/j.1537-2995.2008.01787.x/full