UNC13D and immune system disorder: This is consistent with previous findings that A76V is a deleterious mutation found in patients with GS2 with immunodeficiency and albinism.37,38 Interestingly, residues Y159, S163, and R141 all lie close to each other in the 3-dimensional structure on an outer face of Rab27a, and the structure provides insights into why mutations of these residues might disrupt a possible interaction with Munc13-4.