A small number of genes have also been identified in which rare, moderate penetrance mutations confer greater effects upon PrCa risk, with low-frequency recurrent variants in HOXB13 robustly associated with a greater risk of PrCa of any severity [13–15] and rare germline mutations in BRCA2 associated with a greater risk of aggressive PrCa [16–21]. This evidence concerns the gene HOXB13 and pure red-cell aplasia.