SIL1 and Marinesco-Sjögren syndrome: While unique functions for SIL1 in either BiP-mediated folding or degradation of endogenous clients have largely eluded identification, the discovery that mutations in SIL1 are the leading cause of Marinesco-Sjögren syndrome (MSS) indicates that there are SIL1-specific functions (Anttonen et al., 2005; Senderek et al., 2005).