5'-UTR structural organization, transcript expression, and mutational analysis of the human Rab geranylgeranyl...

Hermansky-Pudlak syndrome (HPS) is a recessively inherited disease with dysfunction of several related subcellular organelles including platelet-dense granules, melanosomes, and lysosomes. Our recent identification of the mutation in murine Rab geranylgeranyl transferase alpha-subunit gene (Rabggta) in one mouse model of HPS, the gunmetal mouse, suggested that human patients with similar phenotypes might have mutations in the human orthologous RABGGTA gene. This prompted reanalysis of the 5'-untranslated structure of the human RABGGTA gene in normal individuals and in patients with deficiencies of platelet-dense granules (alphadelta-SPD), alpha granules (alpha-SPD or gray platelet syndrome, GPS) or alpha plus dense granules (alphadelta-SPD). We report the complete sequence of intron alpha of RABGGTA and demonstrate that exon alpha is immediately upstream of intron alpha. The exon/intron structural organization of the 5'-untranslated region (UTR) of human RABGGTA was found to be similar to that of the mouse Rabggta gene. However, exons alpha and introns alpha are not homologous between mouse and human. Features of the 5'-UTR of RABGGTA suggest it is a housekeeping gene. While obvious disease-causing mutations of human RABGGTA were not found in our existing SPD patients by sequencing its entire coding region, several polymorphisms of RABGGTA including a putative cryptic splicing mutation in intron 4 were identified. Knowledge of the 5'-UTR structure of RABGGTA and its common polymorphisms will be useful for mutation screening or linkage analysis in patients with albinism, thrombocytopenia, or platelet SPD.