Clinical syndromes associated with ASA syndrome defined by MSA antibodies
ASA syndrome is seen in myositis patients with antibodies directed against amino-acyl t-RNA synthetases, which are in charge of facilitating amino acid binding to its cognate t-RNA. The syndromes are associated with one of these antibodies and characterized by combinations of myositis, ILD, rash (mechanic’s hand or DM), Raynaud’s phenomenon, arthritis, and fever in various combinations and severity. Patients never have two anti-t-RNA synthetase antibodies although they may have an associated MAA (usually anti-SSA [52kD]).
• Anti-Jo-1(histidyl tRNA synthetase): most common ASA syndrome seen in 15% of DM and 15% to 30% of PM patients. Accounts for 75% of all patients with ASA syndromes, while each of the other anti-tRNA synthetase antibodies are each found in <5% of patients with an ASA syndrome. Most patients have myositis (80%), rash (30%), seronegative arthritis (60%), Raynaud’s (40%), and fever (25%). Up to 66% have ILD which is a nonspecific interstitial pneumonitis frequently with organizing pneumonia usually involving the lower lobes.
• Anti-PL-7 (threonyl): age of onset averages 60. ILD (90%) is a prominent early symptom. Also has myositis (90%), arthritis (40%), Raynaud’s (40%), mechanic’s hand (30%), and esophageal involvement (20%). Mortality is 15%.
• PL-12 (alanyl): most common in females with average onset age of 50. ILD (90%) is a prominent early symptom. Other manifestations include Raynaud’s (65%), myositis (50%), and pulmonary hypertension (40%).
• Anti-EJ (glycyl): manifestations include ILD (70%), rash (30%), and mild myositis. Frequently associated with another connective tissue disease.
• Anti-OJ (isoleucyl): common manifestations include ILD (90%), mild myositis (90%), DM rash, arthritis, and low-grade fever.
• Other anti-tRNA synthetases (KS, Zo, Ha, Mas, lysyl) have been described in a few patients.