Patients with<unk>  generally have high amounts of high glutamic acid decarboxylase antibody titers. About 80 percent of<unk>  patients have GAD antibodies, compared with about one percent of the general population. The overwhelming majority of people who have GAD antibodies do not contract<unk> , indicating that systematic synthesis of the antibody is not the sole cause of<unk> . GAD, a presynaptic autoantigen, is generally thought to play a key role in the condition, but exact details of the way that autoantibodies affect<unk>  patients are not known. Most<unk>  patients with high-titer GAD antibodies also have antibodies that inhibit GABA-receptor-associated protein (GABARAP). Autoantibodies against amphiphysin and gephyrin are also sometimes found in<unk>  patients. The antibodies appear to interact with antigens in the brain neurons and the spinal cord synapses, causing a functional blockade with gamma-aminobutyric acid. This leads to GABA impairment, which probably causes the stiffness and spasms that characterizes<unk> . There are low GABA levels in the motor cortexes of<unk>  patients. It is not known why GAD autoimmunity occurs in<unk>  patients, and whether<unk>  qualifies as a neuro-autoimmune disorder has been questioned. It is also unknown whether these antibodies are pathogenic. The amount of GAD antibody titers found in<unk>  patients does not correlate with disease severity, indicating that titre levels do not need to be monitored. It has not been proven that GAD antibodies are sole cause of<unk> , and the possibility exists that they are a marker or an epiphenomenon of the condition's cause. In<unk>  patients, motor unit neurons fire involuntarily in a way that resembles a normal contraction. Motor unit potentials fire while the patient is at rest, particularly in the stiff muscles. The excessive firing of motor neurons may be caused by malfunctions in spinal and supra-segmental inhibitory networks that utilize GABA. Involuntary actions show up as voluntary on EMG scans; even when the patient tries to relax, there are agonist and antagonist contractions. In a minority of patients with<unk> , breast, ovarian, or lung cancer manifests paraneoplasticly as proximal muscle stiffness. These cancers are associated with the synaptic proteins amphiphysin and gephyrin. Paraneoplastic<unk>  with amphiphysin antibodies and breast adenocarcinoma tend to occur together. These patients tend not to have GAD antibodies. Passive transfer of the disease by plasma injection has been shown in paraneoplastic<unk>  but not classical<unk> . There is evidence of genetic risk of<unk> . The HLA class II locus makes patients susceptible to the condition. Most<unk>  patients have the DQB1* 0201 allele. This allele is also associated with type 1 diabetes.
Stiff-person syndrome
Parkinson-plus syndrome
Dejerine–Roussy syndrome
Mauriac syndrome
Stiff skin syndrome
Dopamine-responsive dystonia
Huntington's disease-like syndrome
Benign fasciculation syndrome