A Rare Case of Autoimmune-Mediated Lecithin:Cholesterol Acyltransferase Insufficiency Manifesting as the Acute Onset of Extremely Hypo-High-Density Lipoprotein-Cholesterolemia and Spontaneous Improvement: A Case Report with a Review of the Literature.

A 59-year-old Japanese woman was referred for an extremely low level of circulating high-density lipoprotein cholesterol (HDL-C). The serum HDL-C level had long been within the normal range but suddenly decreased asymptomatically to 7 mg/dL. She had no typical symptoms associated with familial lecithin, cholesterol acyltransferase deficiency (FLD), including proteinuria, anemia, and corneal opacity. The circulating level of ApoA-1 was also markedly decreased at 48 mg/dL, and the proportion of esterified cholesterol to free cholesterol was irregularly low at 26%. Whole-genome sequencing revealed no apparent pathological mutations in the LCAT gene. Notably, anti-LCAT antibodies were detected in the serum at 146±1.7 ng/mL, resulting in her being diagnosed with acquired LCAT insufficiency (ALCATI) caused by anti-LCAT antibodies. Five years after her HDL-C levels spontaneously decreased, they increased without any identifiable cause. To our knowledge, only six cases of ALCATI caused by anti-LCAT antibodies have been reported to date. In contrast to the present case, previously reported cases of ALCATI manifested proteinuria that improved with steroid therapy. The unique clinical course in the present case highlights the heterogeneity of ALCATI, warranting further research to clarify the molecular pathophysiology of FLD and ALCATI.