APOE MODENA : A NOVEL APOE MUTANT CAUSING LIPOPROTEIN GLOMERULOPATHY

Lipoprotein glomerulopathy (LPG) is a rare disease characterized by laminated lipid thrombi in the lumina of dilated glomerular capillaries. Apolipoproteins E and B can be demonstrated in these lipid deposits. The plasma lipid profile of LPG patients is similar to that of dysbetalipoproteinemia with elevated IDL and ApoE. Patients often present nephrotic proteinuria but their lipid profile differs from that of nephrotic syndrome secondary to other kidney diseases. LPG has been mainly reported in Japanese and Chinese subjects, associated with novel mutations in APOE gene encoding ApoE. We have identified LPG in an Italian women who at the age of 47 was found to have a combined hyperlipidemia (TC 376 and TG 306 mg/dl) and subsequently developed proteinuria in the nephrotic range. Renal biopsy demonstrated lipoprotein thrombi in glomerular capillaries suggesting LPG. The sequence of APOE gene showed that the patient was: i) homozygous for 2 allele [Cys112 and Cys158 in the mature protein] and ii) heterozygous for a novel mutation in exon 4: c.502 C>T [Arg 150>Cys in the mature protein]. Since the mutant ApoE has a new cysteine residue it is likely that it forms a disulfide bridge with the other Cys residues of the E2 isoforms, resulting in ApoE polymerization (dominant negative effect). This is probably the cause of both dyslipidemia and lipid thrombi in the glomerular capillaries. In view of the poor response of plasma lipids and renal histology and function to statin treatment, the patient started lipid-apheresis with reduction of both dyslipidemia and proteinuria.