Predicted to enable protein tyrosine phosphatase activity. Acts upstream of or within heart development. Predicted to be active in cytoplasm and nucleus. Is expressed in heart and heart tube. Human ortholog(s) of this gene implicated in several diseases, including Addison's disease; Meniere's disease; autoimmune disease (multiple); graft-versus-host disease; and pulmonary tuberculosis. Orthologous to several human genes including PTPN22 (protein tyrosine phosphatase non-receptor type 22).