This GWAS-identified human gene has a fly ortholog, too? Yes, it seems so.
Cheung CL, Lau KS, Ho AY, Lee KK, Tiu SC, Lau EY, Leung J, Tsang MW, Chan KW, Yeung CY, Woo YC, Cheung EY, Hung VH, Pang HK, Hung CS, Sham PC, Kung AW. Genome-wide association study identifies a susceptibility locus for thyrotoxic periodic paralysis at 17q24.3. Nat Genet. 2012 Aug 5. doi: 10.1038/ng.2367. PubMed PMID: 22863731
The top-scoring Drosophila DIOPT result for human KCNJ2 is Irk2.
Other related genes include Ir and Irk3.
The Gal4-UAS system could be used to test RNAi knockdown of these genes, as the FlyBase reports (click gene links above) show that RNAi fly stocks from the Transgenic RNAi Project (TRiP) and Vienna Drosophila RNAi Center (VDRC) exist for these genes.
According to Wikipedia, thyrotoxic periodic paralysis is classified under the larger umbrella of channelopathies, which also include alternating hemiplegia of childhood.