Session Information
Session Type: Abstract Submissions (ACR)
Background/Purpose: Survival of motor neuron (SMN) complex that plays a key role in small nuclear ribonucleoproteins (snRNPs) assembly and interacts with snRNPs has recently been identified as a novel target of autoantibodies in patients with polymyositis/dermatomyositis (PM/DM). Although isolated anti-SMN complex antibodies are uncommon autoantibody specificity associated with PM/DM, their frequent coexistence with anti-snRNPs (U1RNP, Sm) autoantibodies was noticed. Clinical significance of autoantibodies to SMN complex coexisting with anti-snRNPs was examined in unselected cohort of rheumatology clinic.
Methods: Sera from patients enrolled to Center for Autoimmune Disease (n = 1966, including 453 SLE, 132 scleroderma, 125 PM/DM, 130 RA, 61 Sjšgren’s syndrome) were screened for their autoantibody specificities by immunoprecipitation (IP) using 35S-labeled K562 cells extract. Anti-SMN complex antibodies were determined based on IP of the stable SMN complex (~38kD SMN and 120-130kD gemin3 and 4). Antibodies directed to SMN protein were measured by ELISA using SMN recombinant protein. Antibodies to SMN complex were also tested by anti-SMN antigen-capture ELISA using monoclonal antibodies. Clinical information was from the database and chart review.
Results: Anti-snRNPs antibodies were identified in 266 sera (174 anti-U1RNP, 13 anti-U1/U2, and 79 anti-Sm+U1RNP). Although isolated anti-SMN complex antibodies were found previously only in 2 patients with PM, anti-SMN complex antibodies coexisting with anti-snRNPs (11% in anti-U1 or -U1/U2RNP, 6% in anti-Sm+U1RNP) were clearly detected in 28 cases. Prevalence of anti-SMN among anti-snRNPs(+) sera was 14% in Caucasian (P = 0.069 vs African American (AA)), 7% in AA, and 15% in Latin. Levels of anti-SMN antibodies (recombinant protein) were also low in AA (P < 0.005 vs Caucasian, P < 0.05 vs Latin). Clinical features of anti-SMN+snRNPs(+) were compared with anti-snRNPs(+) alone patients (table). Although the diagnosis of SLE and anti-Sm antibodies appears to be less in the anti-SMN+snRNPs(+) group, clinical features of SLE in this group of patients were similar to those of anti-snRNPs(+) patients. Anti-SMN group has more muscle weakness (P = 0.026) and diagnosis of PM/DM (P = 0.051). Diagnosis of SSc (P = 0.022) and features associated with SSc, Raynaud’s phenomenon (P = 0.0008) sclerodactyly (P = 0.016), pitting scars (P = 0.03), and interstitial lung disease are more common in anti-SMN+snRNPs(+) group vs anti-snRNPs(+) alone.
Conclusion: Anti-SMN complex antibodies produced in a tight association with anti-snRNPs are relatively common. Anti-SMN complex antibody positive patients have higher prevalence of clinical features associated with SSc and PM/DM.
Clinical features of anti-SMN+snRNPs vs anti-snRNPs antibody positive patients
|
Anti-SMN + snRNPs (n = 28)
|
Anti-snRNPs (n = 239)
|
||
|
Caucasian |
54% (14/26) |
36% (87/239) |
P = 0.09 |
|
Diagnosis of SLE |
54% (14/26) |
69% (161/235) |
ns |
|
Anti-Sm |
18% (5/28) |
31% (74/238) |
ns |
|
Diagnosis of PM/DM |
8% (2/26) |
3% (6/234) |
ns |
|
Elevated CPK |
21% (4/19) |
30% (55/184) |
ns |
|
Muscle weakness |
26% (6/23) |
9% (19/206) |
P= 0.026 |
|
Diagnosis of SSc |
15% (4/26) |
3% (8/235) |
P = 0.022 |
|
Raynaud’s |
79% (19/24) |
41% (82/198) |
P = 0.0008 |
|
Sclerodactyly |
26% (6/23) |
8% (16/199) |
P = 0.016 |
|
Pitting scars |
26% (6/23) |
10% (19/199) |
P = 0.03 |
|
Interstitial lung disease |
23% (5/22) |
13% (25/198) |
ns |
Disclosure:
J. Y. Chan,
None;
Y. Li,
None;
A. Ceribelli,
None;
E. S. Sobel,
None;
W. H. Reeves,
None;
E. K. L. Chan,
None;
M. Satoh,
None.
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