UNC13D and immune system disorder: Further molecular analysis showed that the interaction between Munc13-4 and Rab27a [which is associated with the immune disorder Griscelli syndrome type 2 (GS2)] is crucial for degranulation and cytotoxicity, and that mutations in Munc13-4 abrogate this interaction (Neeft et al., 2005; Zur Stadt et al., 2006; Menager et al., 2007; Wood et al., 2009).