Component of a complex required to localize phosphatidylinositol 4-kinase (PI4K) to the plasma membrane (PubMed:26571211). The complex acts as a regulator of phosphatidylinositol 4-phosphate (PtdIns(4)P) synthesis (PubMed:26571211). FAM126A plays a key role in oligodendrocytes formation, a cell type with expanded plasma membrane that requires generation of PtdIns(4)P (PubMed:26571211). Its role in oligodendrocytes formation probably explains its importance in myelination of the central and peripheral nervous system (PubMed:26571211, PubMed:16951682). May also have a role in the beta-catenin/Lef signaling pathway (Probable). Component of a phosphatidylinositol 4-kinase (PI4K) complex, composed of PI4KA, EFR3 (EFR3A or EFR3B), TTC7 (TTC7A or TTC7B) and FAM126 (FAM126A or FAM126B) (PubMed:26571211). Interacts with TTC7 (TTC7A or TTC7B), interaction is direct (PubMed:26571211). Localizes to the cytosol and is recruited to the plasma membrane following interaction with other components of the phosphatidylinositol 4-kinase (PI4K) complex. Widely expressed. Highest levels in heart, brain, placenta, spleen and testis. Down-regulated by beta-catenin. The disease is caused by variants affecting the gene represented in this entry. Belongs to the FAM126 family.