Your Query returns 3 Accession Numbers:

Query TermAccessionNCBI TaxonidSynonymsPhenotype (OMIM) *
snRNA:U1:21DNR_0013197227
snRNA:U1:21DNR_0015997227K5    U1    U14    U1a    dU1    U1-1    snRNA1    CR31656    U1-21.1    U1a-21D    U1snRNA    snRNA:U1    U1snRNA21D   
snRNA:U1:21DNT_0337797227K5    U1    U14    U1a    dU1    U1-1    snRNA1    CR31656    U1-21.1    U1a-21D    U1snRNA    snRNA:U1    U1snRNA21D   

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* OMIM link based on symbol match for human and mouse.

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Text2Knowledge ... Yong Huang 2002