diff --git a/content/3.defense-systems/gao_hhe.md b/content/3.defense-systems/gao_hhe.md
index 186a30ac048a0f0c1fb5cb5f114cb33060108b07..ee1822f24a3bf851788d42ddd5e35db07faf0f51 100644
--- a/content/3.defense-systems/gao_hhe.md
+++ b/content/3.defense-systems/gao_hhe.md
@@ -19,7 +19,7 @@ relevantAbstracts:
 # Gao_Hhe
 
 ## Description
-The Gao_hhe system is composed by a single protein. It was predicted through a guilty by association approach independent of domain annotations and validated in a heterologous system {ref:doi=10.1093/nar/gkad317}. It contains a predicted helicase and a Vsr (very short patch repair) endonuclease domain {ref:doi=10.1093/nar/gkad317,10.1128/jvi.00599-23}. 
+The Gao_hhe system is composed by a single protein. It was predicted through a guilty by association approach independent of domain annotations and validated in a heterologous system :ref{doi=10.1093/nar/gkad317}. It contains a predicted helicase and a Vsr (very short patch repair) endonuclease domain :ref{doi=10.1093/nar/gkad317,10.1128/jvi.00599-23}. 
 
 ## Molecular mechanisms
 As far as we are aware, the molecular mechanism is unknown.