Neuromyelitis optica (NMO) is a rare variant of multiple sclerosis (MS) which accounts for approximately 1% of MS cases. Pathological studies and the recent identification of a specific antibody to a cell water channel (aquaporin-4) have led to the conclusion that this is a distinct demyelinating disease.
Antibody mediated autoimmune attack directed against astrocytes primarily in the optic nerve and spinal cord leads to a frequently devastating disease which often leaves patients with vision and mobility impairments. Limited data suggests that standard treatments for MS have little or no effect other than steroids for acute episodes. An association between NMO and other autoimmune diseases has been suggested.
The Australian and New Zealand (ANZ) NMO Collaboration is a team of over 30 neurologists and other researchers across ANZ who have an interest in demyelinating disease. This collaboration has over the past 12 months begun to collect clinical data and serum samples on cases of suspected NMO as well as age and sex-matched MS controls. This project aims to estimate the population prevalence of NMO, define the sensitivity and specificity of the aquaporin-4 antibody test (using several methods) and define the clinical features of NMO in the ANZ population.
The project has three main elements. The first is to screen the collected serum samples in cases with confirmed NMO to look for markers of other auto-immune diseases. The team will also look for any correlations between being positive for NMO IgG and being positive for other autoantibodies.
The second component will use the DNA samples from all identified cases of NMO in ANZ to determine the HLA tissue type most common in cases of NMO. Previous studies have suggested that NMO is not associated with the HLA tissue type most commonly seen in MS (HLA-DRB1*1501) but may be associated with DR3 which is associated with diabetes and other autoimmune diseases.
The third element of the study would be to use the same DNA samples to perform a genome wide association study using chip technology which can test for 700,000 genetic variations at once. This data would be compared with existing data for MS cases and healthy controls which have already been collected and tested through the ANZgene consortium (over 3,000 samples). The aim of this experiment would be to identify any single or small collection of genes which might confer susceptibility to NMO and compare this with the profile of genes that are known to be associated with MS.
It is hoped that this study will help improve the diagnosis of NMO and distinguish it from MS. It may also shed light on the underlying predispositions and pathology of NMO.
The collaboration has recruited 352 cases of NMO and MS. Of these, 159 had suspected NMO, 51 had MS and 100 were healthy comparisons.
Of the 159 suspected NMO cases 69 screened positive for aquaporin-4 antibodies, 25 screened negative for aquaporin-4 antibodies, 33 cases had demyelinating disease confined to the optic nerve or spinal cord, and 32 cases could not be classified.
The prevalence of NMO in this study was 0.33 per 100,000. Unlike MS, there was no clear latitudinal prevalence gradient.
Compared to the people with MS, the NMO group showed a later age of onset, predominantly relapsing-remitting course, and higher levels of disability, incontinence, vision problems, and movement disorder. The prevalence of NMO in Australia and New Zealand was also found to be lower than that reported for North America and Europe.
These results will help to improve the diagnosis of NMO and have also provided new clues into the underlying pathology of NMO and the differences between NMO and MS.
Updated: 04 January, 2012