Redefining progressive encephalomyelitis with rigidity and myoclonus after the discovery of antibodies to glycine receptors.

This review highlights the recent discovery of antibodies to glycine receptor (GlyR-Ab) and discusses the relationship between these antibodies and neurological disorders. Since the initial description in 2008 of antibodies to glycine receptors (GlyR-Abs) in a patient with progressive encephalomyelitis with rigidity and myoclonus (PERM), these antibodies have been found in PERM and in some patients with a variety of stiff person spectrum (SPS) or related disorders. Patients with GlyR-Abs often improve with aggressive immunotherapy, and antibody titres correlate with disease severity. Around 25% of patients have another autoimmune condition and 10-20% have an underlying malignancy. GlyR-Abs bind to extracellular determinants, are mainly Immunoglobulin G1 subclass and induce GlyR internalization in Human embryonic kidney 293 cells, suggesting pathogenicity. The spectrum of neurological disease associated with GlyR-Abs has not been fully characterized, and lower titres may not be syndrome specific, but GlyR-Abs, like antibodies to other neuronal cell-surface antigens, define immunotherapy-responsive disease and are likely to be pathogenic. This distinguishes them from the glutamic acid decarboxylase antibodies that can also be found at high titres in patients with classical stiff person syndrome which is more often chronic and relatively resistant to immunological treatments. Irrespective of the clinical features, GlyR-Abs are helpful in the diagnosis of patients who very often have a subacute, progressive and life-threatening disorder which shows a favourable response to immunotherapy.