Clinical meaning
Vitiligo is a chronic autoimmune disorder characterized by the progressive destruction of melanocytes, the pigment-producing cells located in the basal layer of the epidermis, resulting in well-defined patches of depigmented (white) skin. It affects approximately 0.5-2% of the global population, with onset most commonly between ages 10 and 30 years, and affects all races and ethnicities equally, though it is more noticeable in individuals with darker skin tones. Melanocytes originate from neural crest cells during embryonic development and migrate to the epidermis, hair follicles, eyes, and inner ear. Their primary function is to produce melanin, a pigment that protects underlying cells from ultraviolet (UV) radiation damage by absorbing UV photons and dissipating the energy as heat. Melanin is synthesized within specialized organelles called melanosomes through a series of enzymatic reactions, with tyrosinase being the rate-limiting enzyme. The melanosomes are then transferred to surrounding keratinocytes via dendritic processes, providing UV protection to the entire epidermal layer. In vitiligo, melanocytes are targeted and destroyed by the immune system through several proposed mechanisms. The autoimmune hypothesis, which has the strongest evidence, involves CD8+...