Reader response: Anti-cytosolic 5'-nucleotidase 1A (cN1A) autoantibodies in motor neuron diseases.

Abstract

I read with interest the Clinical/Scientific Note by Dr. Liewluck1 that described 2 patients with motor neuron disease who tested positive for anti-cN1A antibodies by ELISA, a recently identified autoantibody reported to be highly specific for inclusion body myositis (IBM).2 Although an interesting observation, detail regarding the anti-cN1A antibody isotypes identified in both patients was lacking. Some ELISA tests are restricted to the detection of immunoglobulin (Ig) G anti-cN1A antibodies while others may identify the presence of IgG, IgA, or IgM anti-cN1A antibodies, and are potentially somewhat less specific for IBM.3,4 Important differences in the clinical relevance of antibody isotypes was previously noted in other neurologic diseases such as anti–NMDA receptor encephalitis. In this syndrome, IgG antibodies to the NR1 subunit of the NMDA receptor have high specificity, while IgA and IgM antibodies are nonspecific and may be found in patients with mild cognitive impairment or schizophrenia.5 Anti-cN1A antibody isotype data should routinely be included in publications reporting its presence in different patient populations, since this information may provide insight into isotype specificity (or lack thereof) for the diagnosis of IBM.