Healthy

Rare and very rare neurological diseases primarily or exclusively affect the nervous system with a prevalence of \< 5 out of 10'000 and 100'000 people, respectively. Besides these, there are undiagnosed neurological diseases: neurological conditions without a diagnosis after completing a full diagnostic examination. Rare, very rare, and undiagnosed neurological diseases are complicated and progressive and often cause variegated motor signs, impairments, and syndromes. Balance and gait are frequently affected in these conditions, already at the clinical examination. These balance and gait impairments limit activities and cause an increased risk of falling. Falls can eventually result in injuries, even severe. There are only a few studies about these diseases, likely because of their rarity. Hence, the clinical presentation and the course of rare and very rare diseases are poorly known or even unknown. Essential information for these conditions' diagnosis, prognosis, treatment and rehabilitation is missing. MaNeNeND is an observational study underway at the Fondazione IRCCS Istituto Neurologico "Carlo Besta" (Milano) aimed at detailing the clinical and biological features of very