In sickness and in health: the role of TRAPP and associated proteins in disease.

Transport protein particle (TRAPP) represents a series of related protein complexes that function in specific stages of inter-organelle traffic. They share a core of subunits that can activate the GTPase Rab1 through a guanine nucleotide exchange factor (GEF) activity and are distinguished by 'accessory' subunits giving each complex its distinct function. The subunits are ubiquitously expressed and, thus, mutations in TRAPP subunits would be expected to be embryonic lethal. However, since its discovery, a number of subunits have been found to be mutated in several diverse human disorders suggesting that some of these subunits may have cell- or tissue-specific functions. Here we review the current state of knowledge with respect to TRAPP subunit mutations in human disease. We suggest ideas to explain their tissue-specific phenotypes and present avenues for future investigation.