INPP1 (inositol polyphosphate-1-phosphatase) is an Mg2+-dependent phosphatase that catalyzes hydrolysis of the 1-position phosphate from inositol 1,4-bisphosphate and inositol 1,3,4-trisphosphate, key intermediates in phosphoinositide signaling 1. The gene is located on chromosome 2 and comprises six exons spanning >25 kb, with a 1.9 kb mRNA transcript expressed across all tissues, with notably higher levels in testis 2. INPP1 is significantly upregulated in human cancers. Transcription was upregulated in 42 of 49 colorectal tumors 1, and in cervical cancer, miR-27a-mediated INPP1 upregulation promotes cell viability, migration, invasion, and epithelial-mesenchymal transition 3. In osteosarcoma, INPP1 promotes cell migration and invasion through the TGF-β1/Smad2/3 pathway 4. Clinically, INPP1 has relevance to lithium-responsive bipolar disorder. INPP1 was postulated as a lithium target given its role in phospholipase C signaling 2. Genetic variability in INPP1 (rs909270, rs4853694, rs3791809) associates with lithium response and nonresponse in bipolar patients 5 and with suicidal behavior risk in bipolar populations 6. However, one study found INPP1 polymorphisms non-predictive of lithium response in type I bipolar disorder 7, and another identified INPP1 SNP rs2064721 interaction with post-traumatic stress disorder in lithium pharmacogenetics 8.