VPS33B and arthrogryposis: Our hypothesis that mammalian VIPAR and VPS33B are not part of HOPS or CORVET is supported by previous evidence that these two proteins have different functions to their HOPS paralogs in the biogenesis of LROs 20, 21, 41, 57, 60, 61, 62, 63, and that mutations in the genes encoding VPS33B or VIPAR cause a multisystem disorder named arthrogryposis, renal dysfunction and cholestasis syndrome 58, 64.