Lipoprotein glomerulopathy with a new apolipoprotein E phenotype

Lipoprotein glomerulopathy resulting from compound heterogeneous mutations of APOE gene: A case report

RATIONALE

Lipoprotein glomerulopathy (LPG) is a rare glomerular disease characterized by the deposition of lipoprotein thrombi in glomerular capillaries. The disease is characterized by proteinuria, progressive renal failure, and characteristic lipoprotein thrombosis in glomerular capillaries. Rare mutations in the apolipoprotein E (APOE) gene mainly contribute to disease pathogenesis.

PATIENT CONCERNS

A 28-year-old man presented with severe proteinuria and hyperlipidemia. The patient was treated with a full dose of prednisone for 2 months and then combined with leflunomide 20 mg daily for 20 days; however, his edema continued to worsen.

DIAGNOSIS

The patient was diagnosed LPG by laboratory examination and renal biopsy.

INTERVENTIONS

The patient was treated with atorvastatin (20 mg) combined with irbesartan (75 mg) once a day.

OUTCOMES

The patient's lipidaemia and proteinuria were significantly reduced. Genetic testing showed that the patient carried compound heterozygous mutations in APOE. The APOE gene was inherited from her mother and father. Parents with a heterogeneous mutation had normal kidney function without proteinuria.

LESSONS

Usually, a single mutation in APOE can lead to the pathogenesis of LPG. This case shows that LPG could result from compound heterogeneous mutations of the APOE gene inherited from his mother and father. Intensive lipid-lowering combined with RASIs is effective in patients with LPG. Early renal biopsy and genetic mutation detection can avoid the unnecessary use of glucocorticoids and immunosuppressants.

Posttransplant proteinuria due to Apolipoprotein E2 deposition in a kidney allograft

Lipoprotein deposition disorders limited to the kidney and causing proteinuria are rare. We present a case of nephrotic range proteinuria presenting within 4 months after deceased donor renal transplantation in a patient with end-stage kidney disease presumed secondary to hypertension. Two transplant kidney biopsies were performed sixteen weeks after transplantation, and one year after the first biopsy, both showing lipoprotein deposits in the glomeruli, progressive focal segmental glomerulosclerosis, and effacement of visceral foot processes. The patient had a normal lipid profile. Based on previous case reports of Apolipoprotein E variants causing proteinuria in native kidneys, Apolipoprotein E genotyping was performed. Genotyping showed Apolipoprotein E2 homozygosity. This Apolipoprotein E variant has been associated with lipoprotein deposition, proteinuria, and progressive kidney disease in the native kidneys. However, this is the first case of Apolipoprotein E2 homozygosity-related kidney disease in a transplant recipient. The patient was treated with fenofibrate, angiotensin enzyme inhibition, and angiotensin receptor blockade with reduction in proteinuria, and he kept good stable kidney function.

Atherosclerosis, inflammation and lipoprotein glomerulopathy in kidneys of apoE-/-/LDL-/- double knockout mice

BACKGROUND

The apoE-/-/LDL-/- double knockout mice are bearing considerable structural homology to human atherosclerosis. We hypothesized, that advanced lesion formation in the renal artery is associated with kidney alterations in these mice.

METHODS

Kidneys from apoE-/-/LDL-/- double knockout mice at the age of 80 weeks (n = 6) and C57/BL control mice (n = 5) were infused with Microfil, harvested and scanned with micro-CT (12 mum cubic voxels) and Nano-CT (900 nm cubic voxels). We quantitated the total vascular volume using micro-CT. Number and cross-sectional area (microm2) of glomeruli were measured using histology.

RESULTS

At the age of 80 weeks, the renal total vascular volume fraction decreased significantly (p < 0.001) compared to controls. Moreover, the renal artery showed advanced atherosclerotic lesions with adventitial Vasa vasorum neovascularization. Perivascular inflammation was present in kidneys of apoE-/-/LDL-/- double knockout mice, predominantly involved are plasma cells and leucocytes. Glomeruli cross-sectional area (9959 +/- 1083 microm2) and number (24.8 +/- 4.5) increased in apoE-/-/LDL-/- double knockout mice compared to controls (3533 +/- 398 microm2; 17.6 +/- 3, respectively), whereas 41% of the total number of glomeruli showed evidence for lipoprotein associated glomerulopathy (LPG). Moreover, immunohistochemistry demonstrated capillary aneurysms of the glomeruli filled with factor 8 containing emboli.

CONCLUSION

The reduced intra-renal total vascular volume is associated with systemic atherosclerosis and glomeruli alterations in the apoE-/-/LDL-/- double knockout mouse model.

Lipoprotein glomerulopathy: a new apolipoprotein E mutation with enhanced glomerular binding

We describe a case of lipoprotein glomerulopathy, the second ever reported from the United States, in a Mexican man with a hitherto undescribed mutation in the apolipoprotein E gene (substitution of proline for arginine at position 147 [Arg147Pro]). In this patient, glomerular basement membranes showed double contours and circumferential mesangial extensions, suggesting that deposition of lipids could be injurious to endothelial cells. Immunofluorescence staining of thrombi was positive for apolipoprotein E and B. To study the reason for lipid deposition in glomeruli, we incubated normal human kidney sections with serum from the patient and a healthy control. Apolipoprotein E from the patient's serum showed binding to the glomerular capillary wall, but the control did not, suggesting enhanced binding of the mutated apolipoprotein E to glomerular capillaries. Apolipoprotein E genotyping by means of restriction endonuclease digestion of polymerase chain reaction-amplified genomic DNA showed it to be of the wild-type E3/E3.

Disappearance of intraglomerular lipoprotein thrombi and marked improvement of nephrotic syndrome by bezafibrate treatment in a patient with lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a hereditary disorder characterized by intraglomerular lipoprotein thrombi and increased serum apolipoprotein (apo) E. Patients with LPG usually manifest with nephrotic syndrome, and some progress to renal failure; however, no effective therapeutic regimen has been established for this disease. We experienced a patient with LPG for whom bezafibrate treatment was very effective. This 30-year-old Japanese woman had nephrotic syndrome and type III hyperlipoproteinemia. Renal biopsy showed markedly dilated capillary lumina containing massive lipoprotein thrombi. Plasma apo E concentration was elevated to twice that of normal controls. She was proved to be a heterozygote of apo E2 Kyoto (Arg25Cys). After 2 years treatment with bezafibrate (400 mg/day), her plasma albumin gradually increased from 2.1 to 4.0 mg/dl, and intraglomerular lipoprotein thrombi disappeared almost completely. Bezafibrate decreased plasma apo E and dramatically increased high density lipoprotein (HDL)-cholesterol. The decrease in apo E was observed mainly in the pre-beta-fraction, not in the alpha fraction. Lipidological analyses of our patient suggest that the origin her lipoprotein thrombi may be mainly from pre-beta-lipoproteins and that HDL might be involved in resolving lipoprotein thrombi. Our case suggests that administration of fibrates such as bezafibrate may be a novel therapeutic strategy for resolving intraglomerular thrombi and improving nephrotic syndrome in patients with LPG.

Association between apolipoprotein E polymorphism and macroalbuminuria in patients with non-insulin dependent diabetes mellitus

OBJECTIVES

Apolipoprotein E (apo E) is known to play an important role in lipoprotein metabolism through its ability to bind to the receptors as a ligand. Three different apo E alleles (epsilon2, epsilon3 and epsilon4) produce six apo E genotypes (epsilon2/2, epsilon2/3, epsilon2/4, epsilon3/3, epsilon3/4 and epsilon4/4). The objective of this study was to investigate an association between apo E gene polymorphism and macroalbuminuria in 167 Korean patients with non-insulin dependent diabetes mellitus (NIDDM).

METHODS

The patients in the macroalbuminuria group (n = 74) represent those in whom 24 h urinary albumin excretion was above 300 mg. The patients in the normoalbuminuria group (n = 93) represent those in whom 24 h urinary albumin excretion was below 30 mg and serum creatinine levels were less than 1.2 mg/dl. The duration of diabetes in all patients was at least 8 years.

RESULTS

There were no significant differences in terms of age, sex, body mass index, HbA1c, total cholesterol, triglyceride, HDL-cholesterol and LDL-cholesterol between the two groups. In the macroalbuminuria group, the distribution of apo E genotypes revealed epsilon2/2 2 (2.7%), epsilon2/3 14 (18.9%), epsilon2/4 0 (0%), epsilon3/3 47 (63.5%), epsilon3/4 11 (14.9%) and epsilon4/4 0 (0%). In the normoalbuminuria group, the distribution of apo E genotypes revealed epsilon2/2 0 (0%), epsilon2/3 7 (7.5%), epsilon2/4 1 (1.1%), epsilon3/3 72 (77.4%), epsilon3/4 12 (12.9%) and epsilon4/4 1 (1.1%). There was no significant difference in the distribution of apo E genotypes between the two groups. However, there was a significant difference in the allele frequencies, epsilon2 frequency was significantly higher in macroalbuminuria group compared to normoalbuminuria group (12.2% vs 4.3%, P<0.05). Also, we compared apo E carrier frequencies between the two groups. Epsilon2 carrier frequency was significantly higher in macroalbuminuria group compared to normoalbuminuria group (21.6% vs 7.6%, P<0.05). In each group, there was no significant difference in the degree of lipid abnormalities between apo epsilon2 carrier (epsilon2/2, epsilon2/3 genotypes), epsilon3 carrier (epsilon3/3 genotype) and epsilon4 carrier (epsilon3/4, epsilon4/4 genotype).

CONCLUSION

Apo epsilon2 allele and epsilon2 carrier frequencies were significantly higher in macroalbuminuria group. These results suggest that epsilon2 allele may be associated with the development of clinical albuminuria in Korean patients with NIDDM.

A novel apolipoprotein E mutation, E2 (Arg25Cys), in lipoprotein glomerulopathy

BACKGROUND

Lipoprotein glomerulopathy (LPG) is characterized by intraglomerular lipoprotein thrombosis and high plasma concentrations of apolipoprotein (apo) E. An apo E variant, apo E2 (Arg145Pro) Sendai, was recently identified in three patients with LPG. We detected a novel point mutation in the apo E gene in a patient with LPG, and we characterized the mutant apo E.

METHODS

The propositus was a 32-year-old male patient on maintenance hemodialysis because of LPG. The mutation was detected by sequencing of genomic DNA from the patient and was confirmed by restriction fragment length polymorphism (RFLP) with Aor51HI. Recombinant apo E2 (Arg25Cys) Kyoto and normal apo E3 were expressed from COS-1 cells. Low-density lipoprotein (LDL) receptor-binding activities of the variants were determined in an in vitro competition assay.

RESULTS

The propositus had the apo E phenotype E2/E4, as determined by isoelectric focusing, and the genotype epsilon3/epsilon4, as determined by RFLP with HhaI. Sequence analysis of amplified DNA showed a C to T transition, changing the codon for residue 25 from arginine to cysteine. The proband was a heterozygous carrier for apo E2 (Arg25Cys) Kyoto. A family study showed that the mother was a heterozygous carrier of apo E2 Kyoto and had dysbetalipoproteinemia, but no LPG. The pathophysiological effect of this mutation was investigated in vitro by binding studies of recombinant apo E2 Kyoto to LDL receptors on human fibroblasts. The ability of recombinant apo E2 Kyoto to displace LDL was reduced to 10% compared with recombinant apo E3.

CONCLUSIONS

Apo E2 (Arg25Cys) Kyoto is a novel mutation of apo E that is etiologically related to LPG. However, our case indicates that the development of LPG may involve other genetic or environmental factors. Furthermore, our data suggest that arginine-25 of apo E plays an important functional role by influencing the receptor-binding ability of apo E.