Serotonin (5-HT or 5-hydroxytryptamine) is a monoamine primarily known for its role as a neurotransmitter in the central nervous system (CNS). However, the functions of serotonin go beyond its role in the central nervous system: different peripheral tissues have the capacity to produce and/or use serotonin locally, forming systems called micro-serotonergic systems. Among the peripheral roles of serotonin, previous work by the Iron and Immunity team, INSERM U1016, Institut Cochin (Paris), was able to show that serotonin has a positive role on erythropoiesis and the survival of red blood cells, and the team's ongoing work suggests that serotonin also impacts iron metabolism. In humans and in mouse models, several studies have suggested a role for serotonin in pigmentation. In certain syndromic forms of albinism such as Hermansky Pudlak syndrome, platelet serotonin levels are reduced in connection with a decrease in dense platelet granules (delta granules): this characteristic is even part of the diagnostic criteria. Preliminary data from the Iron and Immunity team found: * Changes in serotonin levels in children with albinism compared to control patients, * Changes in hemoglobin level and mean corpuscular volume (MCV) in children with albinism (towards anemia and microcytosis), * Changes in the iron balance in children with albinism (towards iron deficiency). The hypothesis of this research is that peripheral serotonin plays a role in the clinical and biological manifestations of oculocutaneous albinism.