Your Query returns 3 Accession Numbers:

Query TermAccessionNCBI TaxonidSynonymsPhenotype (OMIM) *
U1-1NR_0015997227K5    U1    U14    U1a    dU1    snRNA1    CR31656    U1-21.1    U1a-21D    U1snRNA    snRNA:U1    U1snRNA21D    snRNA:U1:21D   
U1-1NT_0337797227K5    U1    U14    U1a    dU1    snRNA1    CR31656    U1-21.1    U1a-21D    U1snRNA    snRNA:U1    U1snRNA21D    snRNA:U1:21D   
U1-1Z118834113

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

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Text2Knowledge ... Yong Huang 2002