TEST CATALOG ORDERING & RESULTS SPECIMEN HANDLING CUSTOMER SERVICE EDUCATION & INSIGHTS
Test Catalog

Test ID: GLYCS    
Glycine Receptor Alpha1 IgG, Cell Binding Assay, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Evaluating patients with suspected autoimmune stiff-person spectrum disorders (stiff-person syndrome, stiff-limb, stiff trunk or progressive encephalomyelitis with rigidity and myoclonus [PERM]) using serum specimens

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Inhibitory synaptic transmission is mediated by gamma-aminobutyric acid-ergic (GABA-ergic) and glycinergic spinal interneurons, which regulate motor neuron excitability in the brainstem and spinal cord. Autoimmune central nervous system disorders include classic stiff-man syndrome (also known as stiff-person syndrome), limited stiff-man forms (eg, stiff-limb syndrome) and a severe (and sometimes fatal) encephalomyelitic variant known as progressive encephalomyelitis with rigidity and myoclonus (PERM). These disorders are unified clinically by exaggerated startle, stiffness, and spasms of the axis and/or limbs. Characteristic electrophysiologic findings include continuous motor unit activity by unipolar electromyographic (EMG) recording, and exaggerated and non-habituating acoustic startle responses. Eighty percent of patients are seropositive for antibody targeting the 65 kDa isoform of glutamic acid decarboxylase (GAD65).

 

The alpha-1-subunit of the glycine receptor (GlyRa1), which is enriched in brainstem and spinal cord, has emerged as an antigenic target with specificity for the autoimmune stiff-person spectrum, and is particularly useful for diagnostics among patients seronegative for GAD65-IgG. GlyRa1-IgG has been described among patients with PERM (33%), classic stiff-man syndrome (9%), and limited stiff-man forms (17%). Seropositivity for GlyRa1-IgG is detected in 19% of patients from the stiff-man spectrum who are GAD65-IgG seronegative. The clinical context is usually non-paraneoplastic, though thymoma and lymphomas have been occasionally described. Disease-specific antibodies may be detected in serum only, CSF only, or both. Improvements with immunotherapy (steroids, plasma exchange or intravenous immune globulin) occur more commonly in GlyRa1-IgG seropositive patients than among patients seropositive for GAD65 antibody only. In one series, improvement was noted in 6/7 GlyRa1-IgG antibody positive patients compared with only 7/25 without these antibodies.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative

Interpretation Provides information to assist in interpretation of the test results

In the appropriate clinical context, this profile is consistent with a stiff-person syndrome spectrum disorder (classical stiff-person, stiff-limb, or progressive encephalomyelitis with rigidity and myoclonus [PERM]). A paraneoplastic cause should be considered.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Negative results do not exclude autoimmune stiff-person spectrum or cancer.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Hutchinson M, Waters P, McHugh J, et al: Progressive encephalomyelitis, rigidity, and myoclonus: a novel glycine receptor antibody. Neurology. 2008;71:1291-1292

2. McKeon A, Martinez-Hernandez E, Lancaster E, et al: Glycine receptor autoimmune spectrum with stiff-man syndrome phenotype. JAMA Neurol. 2013;70:44-50

3. Carvajal-Gonzalez A, Leite MI, Waters P, et al: Glycine receptor antibodies in PERM and related syndromes: characteristics, clinical features and outcomes. Brain. 2014;137:2178-2192

4. Martinez-Hernandez E, Arino H, McKeon A, et al: Clinical and immunologic investigations in patients with stiff-person spectrum disorder. JAMA Neurol. 2016;73:714-720

5. Hinson SR, Lopez-Chiriboga AS, Bower JH, et al: Glycine receptor modulating antibody predicting treatable stiff-person spectrum disorders. Neurol Neuroimmunol Neuroinflamm. 2018; 5:e438