Mutations in RAB3GAP1, RAB3GAP2, RAB18 and TBC1D20 have previously been shown to cause the autosomal recessive disorder WARBM, which is characterised by abnormalities that affect the ocular and neurological systems (Aligianis et al., 2005; Bem et al., 2011; Borck et al., 2011; Liegel et al., 2013). Here, TBC1D20 is linked to Micro syndrome.