Aging biology may explain why systemic sclerosis looks so different from patient to patient

Systemic sclerosis (SSc) is a rare autoimmune disease marked by vascular injury and progressive fibrosis of the skin and internal organs. Its course varies widely between patients. This narrative review from Iacovantuono and colleagues in EULAR Rheumatology Open (2026) proposes that biological aging, as distinct from chronological age, may be a unifying framework for that heterogeneity, for the comorbidity burden, and for differences in outcome.

The authors begin with the idea that aging is nonlinear. A multiomics study found inflection points near ages 44 and 60. The first is tied to lipid metabolism and cardiovascular change, the second to immune regulation and metabolism. These overlap with peaks in SSc incidence, and most patients develop disease between 40 and 50. Childhood-onset SSc, with first symptoms at a mean age of about 8 to 10 years, suggests that individual aging trajectories, rather than age itself, set when vulnerability appears. The authors stress that a causal link is unproven.

Mechanistically, inflammaging (elevated IL-6, CRP, IL-1β, and TNF) is linked to organ involvement and mortality in SSc, and persistently high CRP is among the most robust prognostic markers across cohorts. Senescent immune cells, fibroblasts, and endothelial cells secrete proinflammatory mediators. Aging-like myeloid bias appears as expanded EGR1⁺ CD14⁺ monocytes. SPP1⁺ macrophages promote lung fibrosis, and interferon-γ-driven CD8⁺ T cells and CXCL13⁺ skin T cells may help perpetuate autoimmunity. Organ-specific findings include telomere shortening and senescence signatures in lung alveolar type II cells in SSc-interstitial lung disease (ILD), a COL8A1/ACTA2⁺ senescent myofibroblast population in skin, and endothelial-to-mesenchymal transition that tracks with fibroblast senescence and CCN2. Pulmonary age was the strongest predictor of mortality in one analysis.

Clinically, a German registry of over 3,000 patients found that 24.5% had first non-Raynaud's manifestations before age 40 and 22.5% after age 60. Late-onset disease (usually 60 or older) brings more pulmonary arterial hypertension, fewer digital ulcers, milder skin disease, more anticentromere antibodies, and worse survival. Standardized mortality ratios against the general population are higher in younger-onset patients, though. Juvenile SSc is more often diffuse, with less ILD, pulmonary hypertension, and renal crisis. Older age predicts incident ILD and lung function decline, and it is built into the ILD-RISC screening score.

Comorbidities follow age-related patterns. Pooled hazard ratios versus the general population were 1.64 for stroke and 2.12 for cardiovascular disease. In a Danish cohort of 1,569 patients, heart failure risk was higher in those 55 or younger (HR 4.14) than in older patients (HR 2.74). Cancer risk was 75% higher (RR 1.75), and cancer mortality was elevated (SMR 3.13 in an Australian cohort of 1,727). Osteoporosis prevalence was 27% across 1,839 patients, with hip fractures occurring earlier (67.2 vs 75.2 years). Premature ovarian insufficiency risk was raised at ages 30 to 40 (HR 1.8).

The key caveat is that most studies use chronological age or subtype markers rather than direct measures of biological aging. The authors note inconsistent late-onset definitions (60, 65, or 70 years), scarce cardiac tissue data, and difficulty separating SSc organ damage from age-related decline or comorbidity. They call for a standardized, biologically meaningful age cut-off in trials.