This special case corresponds to the “traits” being (the same measure of) a single trait; in other words, applying MTAG instead of inverse-variance-weighted meta-analysis to T GWAS results. Doing so can be useful if there is sample overlap in the GWAS results. In this case, as noted in the main text, MTAG specializes to β^MTAG,j,t=1′∑j−11′∑j−11β^j for all t, and it is no longer necessary to estimate Ω.
