Two Cases of Acquired High-Density Lipoprotein Deficiency with Immunoglobulin G4-Related Lecithin-Cholesterol Acyltransferase Autoantibody

Lecithin-cholesterol acyltransferase (LCAT) plays a significant role in the progression from premature to mature high-density lipoprotein (HDL) in circulation. Consequently, primary or secondary LCAT deletion or reduction naturally results in low serum HDL cholesterol levels. Recently, rare cases of acquired HDL deficiency with LCAT autoantibodies have been reported, mainly from Japan, where LCAT autoantibodies of immunoglobulin G (IgG) caused the HDL deficiency. Here to our knowledge, we report for the first time two cases of acquired HDL deficiency caused by IgG4 linked LCAT autoantibodies with or without a high serum IgG4 level. Furthermore, these cases can extend to a new concept of "IgG4 autoimmune disease" from the viewpoint of verifying the serum autoantibody and/or renal histopathology.