International Day of Alternating Hemiplegia Syndrome

January 18, International Day of Alternating Hemiplegia Syndrome, is established as a global landmark to raise awareness of an extremely rare neurological disease with an estimated prevalence of one case per million people. It almost always begins in early childhood and profoundly impacts the motor, neurological, and functional development of those affected. Alternating Hemiplegia Syndrome is a neurological disorder characterized by recurrent episodes of weakness or paralysis that can alternately affect one side of the body, and in more severe cases, temporarily compromise both sides. These intermittent but recurrent manifestations create a significant burden for families and healthcare systems, as they require specialized neurological follow-up, rehabilitation therapy, nutritional support, and cognitive and psychosocial approaches throughout life. The diagnostic process is based on a detailed clinical evaluation accompanied by genetic studies aimed at detecting mutations in the ATP1A3 gene, in addition to excluding other neurological pathologies with similar symptoms. Despite its low population frequency, the complexity of its presentation makes this condition a constant challenge for neurological practice. The first signs usually appear before 18 months of age, with motor crises that come and go, characteristically with sleep, a trait that helps differentiate this syndrome from other neurological disorders. Approximately 80% of reported cases are explained by alterations in this gene, although questions remain about other possible genetic and biological mechanisms. In addition to hemiplegia episodes, people with this syndrome often experience dystonic attacks, hypotonia, abnormal eye movements, and dysfunctions of the autonomic system. These episodes vary widely in duration, from minutes to several days, and constitute the most distinctive clinical manifestation of the disease. Internationally, organizations and family associations use this day to disseminate data, share clinical experiences, and promote cooperation between specialized centers, strengthening care capabilities and making visible a condition that, due to its rarity, risks remaining on the margins of health priorities. International Day of Alternating Hemiplegia Syndrome represents a strategic opportunity to turn rarity into collective awareness, placing at the center of the discussion a disease that, although it affects few, profoundly and sustainably impacts those who live with it and their communities. This gene encodes essential components for neuronal function, and its alteration causes a highly variable clinical expression, ranging from episodic paralysis to combinations of motor, ocular, and autonomic disorders. During attacks, not only is strength affected, but also muscle tone, voluntary coordination, and eye motility, in addition to registering paroxysmal symptoms such as dystonias, rigidity, and autonomic alterations. The specialized literature emphasizes that translational research and the development of targeted therapies constitute a priority to improve the functional prognosis and quality of life. The choice of January 18 as a commemorative date responds to the scientific recognition of the role of ATP1A3 in the etiology of this disease, and has become a platform to mobilize communities, health professionals, and patient networks around a shared agenda of information, support, and knowledge generation. However, there is currently no curative treatment, and the approach focuses on symptomatic management, prevention of complications, and comprehensive support for the patient and their environment. Over time, a significant proportion of patients develop psychomotor retardation, ataxia, and other neurological deficits, reflecting the progressive and multisystemic nature of the condition. At the molecular level, most cases are related to mutations in the ATP1A3 gene, identified as the main genetic determinant of the disease since 2012, a year that also gave rise to the international commemoration of January 18.