Your Query returns 7 Accession Numbers:

Query TermAccessionNCBI TaxonidSynonymsPhenotype (OMIM) *
Nkx2.5NM_00870010090Csx    tinman    Nkx-2.5    Nkx2-5   
NKX2.5BC0257119606CSX1    CSX    NKX2E    NKX2-5   
NKX2.5NM_0043879606CSX    CSX1    NKX2E    NKX2-5   
Nkx2.5NM_05365110116Nkx2-5    Csx   
Nkx2.5S835177955
nkx2.5U665727955
nkx2.5NM_1314217955nk2.5    nkx2-5   

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

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Text2Knowledge ... Yong Huang 2002