Pseudokinase that acts as an allosteric activator of the Golgi serine/threonine protein kinase FAM20C and is involved in biomineralization of teeth. Forms a complex with FAM20C and increases the ability of FAM20C to phosphorylate the proteins that form the 'matrix' that guides the deposition of the enamel minerals. Interacts with FAM20C; probably forming a heterotetramer of 2 subunits of FAM20A and 2 subunits of FAM20C. In the mammary gland, expressed at higher levels in lactating mice than in virgin mice (PubMed:29858230). Observed throughout the tissues of the mandibular incisor, including the secretory and maturation stage ameloblasts, the suprabasal layers of the gingival epithelium and the odontoblasts. Weak expression in the enamel matrix. In EML and MPRO cell lines, low levels in undifferentiated cells. Induced during maturation to promyelocyte stage of neutrophil differentiation. Decreased during neutrophil terminal differentiation. By all-trans retinoic acid (atRA) and IL3 in EML cell line. N-glycosylated. Mice survive to adulthood and show biomineralization defects such as severe amelogenesis imperfecta (AI). In addition, mice develop disseminated calcifications of muscular arteries and intrapulmonary calcifications, similar to those of fetuin-A (Ahsg) deficient mice, although they are normocalcemic and normophosphatemic, with normal dentin and bone. Belongs to the FAM20 family.