Among the autoantibodies most frequently associated with manifestations mimicking neurodegenerative disorders—such as dementia, parkinsonism, ataxia and motor neuron disease—IgLON5-, LGI1- and CASPR2-antibodies, predominantly of the IgG4 subclass and associated with specific HLA haplotypes, are the most common. The gene discussed is IGLON5; the disease is motor neuron disorder.