abnormal melanosome morphology abnormal melanosome maturation 2018-11-19T13:55:56Z any anomaly in the developmental processes that are required for a melanosome to attain its fully functional state; melanosome maturation occurs through sequential stages (I-IV) that can be defined based on morphology and melanin content; stage I pre-melanosomes are roughly spherical, lack pigment, contain intraluminal vesicles, and resemble multivesicular bodies i.e. structures found along the endosomal pathway; stage II melanosomes are elongated (ellipsoidal) in shape, lack pigment, and contain intraluminal matrix fibers organized in a striated array; deposition of melanin along the matrix fibers begins in stage III melanosomes; stage IV melanosomes, corresponding to fully-melanized mature organelles, are characterized by a dense homogeneous deposit of melanin that covers all the internal structures of the matrix MP:0030915 MPheno.ontology