Intragroup comparisons of demographics and complement C4 genes in patients with IIM with and without MSA or MAA
| Continuous data | Ab-negative | Ab-positive | P value | |
| Age of diagnosis, mean±SD (years old) | ||||
| MSA | 51.8±14.6 | 51.3±14.2 | 0.66 | |
| MAA | 52.9±14.0 | 47.6±15.0 | 2.2E-05 | |
| MSA-Jo1 | 52.2±14.6 | 48.9±13.1 | 0.02 | |
| MAA-PM/Scl | 52.3±14.1 | 43.6±15.1 | 8.5E-06 | |
| MAA-Ro | 51.5±14.5 | 52.5±13.3 | 0.63 | |
| C4T, GCN, mean±SD | ||||
| MSA | 3.46±0.78 | 3.51±0.78 | 0.29 | |
| MAA | 3.55±0.79 | 3.39±0.75 | 0.0004 | |
| MSA-Jo1 | 3.55±0.78 | 3.25±0.75 | 2.4E-08 | |
| MAA-PM/Scl | 3.53±0.79 | 3.13±0.67 | 2.4E-06 | |
| MAA-Ro | 3.46±0.78 | 3.40±0.72 | 0.38 | |
| C4A GCN, mean±SD | ||||
| MSA | 1.79±0.92 | 1.68±0.86 | 0.02 | |
| MAA | 1.80±0.89 | 1.59±0.85 | 3.9E-05 | |
| MSA-Jo1 | 1.79±0.87 | 1.43±0.86 | 2.0E-09 | |
| MAA-PM/Scl | 1.78±0.90 | 1.34±0.72 | 5.3E-06 | |
| MAA-Ro | 1.69±0.88 | 1.52±0.77 | 0.028 | |
| C4B GCN, mean±SD | ||||
| MSA | 1.68±0.59 | 1.79±0.56 | 0.0005 | |
| MAA | 1.73±0.59 | 1.77±0.54 | 0.143 | |
| MSA-Jo1 | 1.73±0.59 | 1.80±0.52 | 0.087 | |
| MAA-PM/Scl | 1.73±0.59 | 1.79±0.46 | 0.329 | |
| MAA-Ro | 1.74±0.60 | 1.83±0.51 | 0.072 | |
| C4L GCN, mean±SD | ||||
| MSA | 2.35±1.11 | 2.40±1.14 | 0.454 | |
| MAA | 2.48±1.14 | 2.27±1.12 | 0.0017 | |
| MSA-Jo1 | 2.50±1.13 | 2.02±1.11 | 2.1E-09 | |
| MAA-PM/Scl | 2.47±1.14 | 1.80±1.00 | 1.7E-07 | |
| MAA-Ro | 2.36±1.17 | 2.35±1.10 | 0.91 | |
| C4S GCN, mean±SD | ||||
| MSA | 1.04±0.70 | 1.10±0.74 | 0.093 | |
| MAA | 1.03±0.72 | 1.11±0.72 | 0.055 | |
| MSA-Jo1 | 1.02±0.71 | 1.26±0.72 | 1.2E-06 | |
| MAA-PM/Scl | 1.03±0.71 | 1.35±0.61 | 6.8E-05 | |
| MAA-Ro | 1.08±0.72 | 1.13±0.69 | 0.50 | |
| Categorical data | Ab-negative | Ab-positive | P value | OR |
| Sex, female, % | ||||
| MSA | 62.1 | 70.7 | 0.001 | 1.47 (1.17–1.86) |
| MAA | 64.3 | 72.8 | 0.0012 | 1.49 (1.17–1.90) |
| MSA-Jo1 | 66.3 | 69.4 | 0.33 | ns |
| MAA-PM/Scl | 65.2 | 74.7 | 0.059 | 1.58 (0.968–2.57) |
| MAA-Ro | 65.6 | 73.9 | 0.051 | 1.49 (0.983–2.24) |
| C4T=2+3, frequency, % | ||||
| MSA | 56.0 | 51.7 | 0.119 | |
| MAA | 49.1 | 61.4 | 1.2E-05 | 1.65 (1.32–2.07) |
| MSA-Jo1 | 49.5 | 69.8 | 1.3E-09 | 2.36 (1.77–3.14) |
| MAA-PM/Scl | 49.9 | 80.2 | 7.5E-09 | 4.08 (2.40–6.92) |
| MAA-Ro | 54.1 | 59.1 | 0.27 | |
| C4A=0+1, frequency, % | ||||
| MSA | 40.7 | 45.6 | 0.077 | 1.22 (0.98–1.52) |
| MAA | 39.0 | 52.0 | 3.6E-06 | 1.69 (1.36–2.12) |
| MSA-Jo1 | 38.7 | 63.6 | 1.7E-13 | 2.77 (2.10–3.66) |
| MAA-PM/Scl | 39.8 | 67.0 | 4.6E-07 | 3.08 (1.96–4.85) |
| MAA-Ro | 45.0 | 54.0 | 0.05 | 1.44 (0.999–2.07) |
| C4B=0+1, frequency, % | ||||
| MSA | 32.9 | 26.0 | 0.0065 | 0.72 (0.56–0.91) |
| MAA | 31.0 | 25.0 | 0.018 | 0.74 (0.58–0.95) |
| MSA-Jo1 | 30.7 | 24.3 | 0.057 | 0.74 (0.55–1.01) |
| MAA-PM/Scl | 30.7 | 22.2 | 0.085 | 0.65 (0.39–1.08) |
| MAA-Ro | 30.1 | 21.0 | 0.026 | 0.62 (0.40–0.96) |
| C4L=0+1+2, frequency, % | ||||
| MSA | 58.0 | 55.1 | 0.30 | |
| MAA | 52.4 | 62.0 | 0.0009 | 1.48 (1.17–1.87) |
| MSA-Jo1 | 51.6 | 73.5 | 1.1E-10 | 2.60 (1.92–3.52) |
| MAA-PM/Scl | 53.1 | 82.1 | 6.6E-08 | 4.07 (2.30–7.21) |
| MAA-Ro | 57.9 | 55.8 | 0.653 | |
| C4S=0, frequency, % | ||||
| MSA | 21.6 | 19.8 | 0.43 | |
| MAA | 22.4 | 18.6 | 0.11 | |
| MSA-Jo1 | 23.1 | 12.4 | 6.2E-05 | 0.47 (0.32–0.70) |
| MAA-PM/Scl | 22.6 | 6.0 | 4.9E-05 | 0.22 (0.09–0.54) |
| MAA-Ro | 20.8 | 16.5 | 0.253 | |
C4A, acidic isotype of complement C4; C4B, basic isotype of complement C4; C4L, long form of C4 gene with human endogenous retrovirus HERV-K(C4); C4S, short form of C4 gene without integration of the retrovirus HERV-K(C4); GCN, gene copy number; IIM, idiopathic inflammatory myopathies; MAA, myositis-associated autoantibodies; MSA, myositis-specific autoantibodies.