A kit for predicting prognosis of a brain disease caused by microplastic exposure, comprising a probe specifically binding to one or more genes, a primer for amplifying the one or more genes, an antibody specifically binding to a protein encoded by the one or more genes, or a peptide having a binding domain specific to the protein, wherein the one or more genes are selected from the group consisting of Tceanc (transcription elongation factor A N-terminal and central domain containing), Mx1 (MX dynamin like GTPase 1), Ms4a6d (membrane-spanning 4-domains, subfamily A, member 6D), Arc (activity regulated cytoskeletal-associated protein), Olfr912 (olfactory receptor 912), Casc5 (kinetochore scaffold 1), Egr3 (Early growth response 3), Gm11565 (predicted gene 11565), Gabra6 (gamma-aminobutyric acid (GABA) A receptor, subunit alpha 6), Cdkn1a (cyclin-dependent kinase inhibitor 1A (P21)), Egr1 (early growth response 1), Zfp184 (zinc finger protein 184 (Kruppel-like)), Ms4a14 (membrane-spanning 4-domains, subfamily A, member 14), Tas2r121 (taste receptor, type 2, member 121), AB124611 (cDNA sequence AB124611), Irs4 (insulin receptor substrate 4), Fut2 (fucosyltransferase 2), Gm10754 (predicted gene 10754), Rgs21 (regulator of G-protein signalling 21), Srsx (serine-rich, secreted, X-linked), Rad51b (RAD51 paralog B), Nr4a1 (nuclear receptor subfamily 4, group A, member 1), Olfr1442 (olfactory receptor 1442), 1700074P13Rik (RIKEN cDNA 1700074P13 gene), Ctla2a (cytotoxic T lymphocyte-associated protein 2 alpha), Ifit3b (interferon-induced protein with tetratricopeptide repeats 3B), Gm4924 (predicted gene 4924), Vmn2r95 (vomeronasal 2, receptor 95), Trpc7 (transient receptor potential cation channel, subfamily C, member 7), Smc4 (structural maintenance of chromosomes 4), Sult1c1 (sulfotransferase family, cytosolic, 1C, member 1), Tg (thyroglobulin), Dusp1 (dual specificity phosphatase 1), Ptpn20 (protein tyrosine phosphatase, non-receptor type 20), Tex14 (testis expressed gene 14), Bhlhe23 (basic helix-loop-helix family, member e23), Loxl2 (lysyl oxidase like 2), Rora (RAR-related orphan receptor alpha), Nrap (nebulin-related anchoring protein), Olfr435 (olfactory receptor 435), Htr2a (5-hydroxytryptamine (serotonin) receptor 2A), Fcer1g (Fc receptor, IgE, high affinity I, gamma polypeptide), Ecscr (endothelial cell surface expressed chemotaxis and apoptosis regulator), Lrrk2 (leucine-rich repeat kinase 2), Ddx51 (DEAD box helicase 51), Olfr1284 (olfactory receptor 1284), Stfa2l1 (stefin A2 like 1), Parpbp (PARP1 binding protein), Drd5 (dopamine receptor D5), Olfr1352 (olfactory receptor 1352), Olfr1303 (olfactory receptor 1303), Eif2ak2 (eukaryotic translation initiation factor 2-alpha kinase 2), Eme1 (essential meiotic structure-specific endonuclease 1), Pcbd1 (pterin 4 alpha carbinolamine dehydratase/dimerization cofactor of hepatocyte nuclear factor 1 alpha (TCF1) 1), Clic1 (chloride intracellular channel 1), Itgb1bp1 (integrin beta 1 binding protein 1), Serpinb3c (serine (or cysteine) peptidase inhibitor, clade B, member 3C), BC048671 (cDNA sequence BC048671), Zfy2 (zinc finger protein 2, Y-linked), and Gm20865 (predicted gene, 20865).