This definition appears very rarely
Using 265 families from the Multiple Autoimmune Disease Genetics Consortium (MADGC), Criswell et al.  compared the frequency of ADs in siblings of multiplex families stratified by seven ADs: AITD, RA, MS, SLE, T1D, IBD and PSO. These diseases were pre-specified given a variety of considerations. There was no evidence of familial autoimmunity except in the case of IBD patients in whose families MS was observed among FDRs (OR: 8.