The occurrence of various collagen diseases in one family: a sister with ISSc, PBC, APS, and SS and a brother with systemic lupus erythematosus.

We encountered siblings who had collagen diseases and related symptoms. Case 1 was a 53‐year‐old woman who had limited cutaneous systemic sclerosis (ISSc) associated with primary biliary cirrhosis (PBC), antiphospholipid antibody syndrome (APS), and subclinical Sjögren's syndrome (SS). Case 2 was a 48‐year‐old man, her younger brother, with systemic lupus erythematosus (SLE) that developed at 32 years of age. Investigation of their family revealed that their mother had Raynaud's phenomenon, arthritis, and subclinical Sjögren's syndrome, and that another younger brother of Cases 1 and 2 had Raynaud's phenomenon and general fatigue. HLA analysis revealed that the sister and brother had some identical HLA antigens in common, including A2, A33 (19), B67, B44 (12), Cw7, DR2, DR6, DR52, and DQ1. The sister, brother and their mother had common HLA antigens including A2, B67, Cw7, DR2, and DQ1. Although Cases 1 and 2 shared the same HLA system, they presented different phenotypes of collagen disease.