What syndromes are associated with antibodies to SS A (Ro)?
Antibodies to SS-A/Ro may target one or both of two cellular proteins with different molecular weights (52 kDa and 60 kDa) and cellular locations. The 52-kDa protein is an interferon-inducible protein located in the cytoplasm. It functions as an E3 ubiquitin ligase that adds ubiquitin to several proteins involved in the inflammatory and immune response resulting in their accelerated degradation. The 60-kDa protein binds to small noncoding RNAs located in the nucleus. It functions as an RNA chaperone that binds to defective cellular and viral RNAs to hasten their degradation. Diseases associated with these antibodies include:
- • SLE
- • Primary Sjögren’s syndrome
- • Subacute cutaneous lupus (a variant of lupus characterized by prominent photosensitivity and rash)
- • Neonatal lupus
- • Congenital heart block
- • Undifferentiated connective tissue disease
- • Neuromyelitis optica spectrum disorder
- • Other diseases: primary biliary cirrhosis (30%), anti-tRNA synthetase polymyositis (19%), systemic sclerosis (10%–20%)
Notably some diseases have antibodies directed preferentially against one of the two SS-A/Ro proteins. Antibodies primarily against 52 kDa SS-A/Ro are seen in patients with anti-tRNA polymyositis and in patients with systemic sclerosis. Patients with the other autoimmune diseases listed earlier typically have antibodies against both 52 kDa and 60 kDa SS-A/Ro proteins.