Lipoprotein glomerulopathy with a novel apolipoprotein E variant, APOE Kanto (Asp 151dup)

A 33-year-old Japanese man was admitted for possible kidney disease because of massive proteinuria. Laboratory findings were characterized by marked urinary protein of 4.7 g/day and high-serum triglyceride levels of 266 mg/dL. Renal biopsy revealed segmental proliferation in the mesangium and lipoprotein thrombi in the glomerular capillary. These results suggested that the diagnosis was lipoprotein glomerulopathy (LPG), although serum apolipoprotein E (apo E) levels were within normal ranges. The APOE phenotype was identified as E2/3 by isoelectric focusing polyacrylamide gel electrophoresis. Direct DNA sequencing analyses for apo E identified a duplication of amino acid 151, aspartic acid, and the gene mutation was named APOE Kanto. APOE gene mutations due to amino acid duplication are rare, and this is the first report showing that amino acid duplication among apo E gene mutations is involved in LPG. It is also noteworthy that the patient developed end-stage kidney disease after over than 10 years despite fibrate treatment.

Impact of Apolipoprotein E Variants: A Review of Naturally Occurring Variants and Clinical Features

Apolipoprotein E (apoE) is a key apoprotein in lipid transport and is susceptible to genetic mutations. ApoE variants have been studied for four decades and more than a hundred of them have been reported. This paper presents an up-to-date review of the function and structure of apoE in lipid metabolism, the E2, E3, and E4 isoforms, the APOE gene, and various pathologies, such as familial type III hyperlipidemia and lipoprotein glomerulopathy, caused by apoE variants. Alzheimer's disease was barely mentioned in this paper. But this review should help researchers obtain a comprehensive overview of human apoE in lipid metabolism.

Whole Exome Sequencing Reveals a Novel APOE Mutation in a Patient With Sporadic Early-Onset Alzheimer's Disease

Apolipoprotein (APOE) is implicated and verified as the main risk factor for early-onset Alzheimer's disease (AD). APOE is a protein that binds to lipids and is involved in cholesterol stability. Our paper reports a case of a sporadic early-onset AD (sEOAD) patient of a 54-year-old Korean man, where a novel APOE Leu159Pro heterozygous mutation was revealed upon Whole Exome Sequence analysis. The proband's CSF showed downregulated levels of Aβ42, with unchanged Tau levels. The mutation is in the Low-Density Lipoprotein Receptor (LDLR) region of the APOE gene, which mediates the clearance of APOE lipoproteins. LDLR works as a high-affinity point for APOE. Studies suggest that APOE-LDLR interplay could have varying effects. The LDLR receptor pathway has been previously suggested as a therapeutic target to treat tauopathy. However, the APOE-LDLR interaction has also shown a significant correlation with memory retention. Leu159Pro could be an interesting mutation that could be responsible for a less damaging pattern of AD by suppressing tau-association neurodegeneration while affecting the patient's memory retention and cognitive performance.

An Updated Review and Meta Analysis of Lipoprotein Glomerulopathy

More than 200 cases of lipoprotein glomerulopathy (LPG) have been reported since it was first discovered 30 years ago. Although relatively rare, LPG is clinically an important cause of nephrotic syndrome and end-stage renal disease. Mutations in the APOE gene are the leading cause of LPG. APOE mutations are an important determinant of lipid profiles and cardiovascular health in the population and can precipitate dysbetalipoproteinemia and glomerulopathy. Apolipoprotein E-related glomerular disorders include APOE2 homozygote glomerulopathy and LPG with heterozygous APOE mutations. In recent years, there has been a rapid increase in the number of LPG case reports and some progress in research into the mechanism and animal models of LPG. We consequently need to update recent epidemiological studies and the molecular mechanisms of LPG. This endeavor may help us not only to diagnose and treat LPG in a more personized manner but also to better understand the potential relationship between lipids and the kidney.

A novel apolipoprotein E mutation, ApoE Ganzhou (Arg43Cys), in a Chinese son and his father with lipoprotein glomerulopathy: two case reports

Background

Lipoprotein glomerulopathy is a rare and newly recognized glomerular disease that can lead to kidney failure. Its pathological features include the presence of lipoprotein embolus in the loop cavity of glomerular capillaries. It is believed that apolipoprotein E gene mutation is the initiator of the disease. Since the discovery of lipoprotein glomerulopathy, 16 different apolipoprotein E mutations have been reported worldwide, but most of these cases are sporadic. Here we report two cases of lipoprotein glomerulopathy, a Chinese son and his father, with a novel apolipoprotein E mutation, ApoE Ganzhou (Arg43Cys).

Case presentation

Case 1, a 33-year-old Chinese man, was hospitalized on 3 March 2014 owing to edema and weakness of facial and lower limbs for 1 month. Laboratory data showed urine protein 3+, hematuria 2+, serum creatinine 203 μmol/L, uric acid 670 μmol/L, total cholesterol 12.91 mmol/L, triglyceride 5.61 mmol/L, high-density lipoprotein 1.3 mmol/L, low-density lipoprotein 7.24 mmol/L, apolipoprotein B 2.48 g/L, and lipid protein (a) 571 mg/L. Renal tissue examined by immunofluorescence and electron microscopy indicated lipoprotein glomerulopathy. Case 2, 55-year-old father of case 1, was hospitalized on 12 January 2016 owing to edema of his lower extremities for 6 months. Laboratory data showed urine protein 2+, hematuria 2+, serum creatinine 95 μmol/L, uric acid 440 μmol/L, total cholesterol 4.97 mmol/L, triglyceride 1.91 mmol/L, high-density lipoprotein 1.18 mmol/L, low-density lipoprotein 3.12 mmol/L, apolipoprotein B 2.48 g/L, and lipid protein (a) 196 mg/L. Renal tissue examined by immunofluorescence and electron microscopy indicated lipoprotein glomerulopathy. Apolipoprotein E mutation test showed that they had the same gene mutation, a novel type of apolipoprotein E mutation.

Based on their clinical presentation and examination findings, they were diagnosed with lipoprotein glomerulopathy. Case 1 was treated with prednisone and dual plasma replacement, followed by simvastatin, nifedipine, triptolide, and angiotensin II receptor blocker drug therapy. After 1 month, the edema symptoms of the patient were alleviated, and urinary protein, serum creatinine, and uric acid were quantitatively reduced. Case 2 was treated with Tripterygium wilfordii and angiotensin II receptor blocker drugs for 3 weeks, and his edema symptoms were alleviated, and urinary protein, serum creatinine, and uric acid were quantitatively reduced.

Conclusions

The apolipoprotein E mutation in the two cases we reported was a familial aggregation phenomenon, and the mutation is a novel type, which we named ApoE Ganzhou (Arg43Cys). The location of the gene mutation is close to the most common mutation type of lipoprotein glomerulopathy, ApoE Kyoto (Arg25Cys), so we speculate that its pathogenic role might be the similar to that of ApoE Kyoto (Arg25Cys).

Lipoprotein glomerulopathy associated with the Osaka/Kurashiki APOE variant: two cases identified in Latin America

Background

Lipoprotein glomerulopathy (LPG) is a rare autosomal dominant disease caused by mutations in APOE, the gene which encodes apolipoprotein E. LPG mainly affects Asian individuals, however occasional cases have also been described in Americans and Europeans. Herein we report two unrelated Brazilian patients with LPG in whom genetic analyses revealed the APOE-Osaka/Kurashiki variant.

Case presentation - case 1

A 29-year-old Caucasian male sought medical attention with complaints of face swelling and foamy urine for the last 3 months. He denied a family history of kidney disease, consanguinity, or Asian ancestry. His tests showed proteinuria of 12.5 g/24 h, hematuria, serum creatinine 0.94 mg/dL, albumin 2.3 g/dl, total cholesterol 284 mg/dL, LDL 200 mg/dL, triglycerides 175 mg/dL, and negative screening for secondary causes of glomerulopathy. A kidney biopsy revealed intraluminal, laminated deposits of hyaline material in glomerular capillaries consistent with lipoprotein thrombi. These findings were confirmed by electron microscopy, establishing the diagnosis of LPG. His apolipoprotein E serum level was 72 mg/dL and genetic analysis revealed the APOE pathogenic variant c.527G > C, p.Arg176Pro in heterozygosis, known as the Osaka/Kurashiki mutation and positioned nearby the LDL receptor binding site.

Case 2

A 34-year-old Caucasian man sought medical assessment for renal dysfunction and hypertension. He reported intermittent episodes of lower-limb edema for 3 years and a family history of kidney disease, but denied Asian ancestry. Laboratorial tests showed BUN 99 mg/dL, creatinine 10.7 mg/dL, total cholesterol 155 mg/dL, LDL 79 mg/dL, triglycerides 277 mg/dL, albumin 3.1 g/dL, proteinuria 2.7 g/24 h, and negative screening for secondary causes of glomerulopathy. His kidney biopsy was consistent with advanced chronic nephropathy secondary to LPG. A genetic analysis also revealed the Osaka/Kurashiki variant. He was transplanted a year ago, displaying no signs of disease relapse.

Conclusion

We report two unrelated cases of Brazilian patients with a diagnosis of lipoprotein glomerulopathy whose genetic assessment identified the APOE-Osaka/Kurashiki pathogenic variant, previously only described in eastern Asians. While this is the second report of LPG in Latin America, the identification of two unrelated cases by our medical team raises the possibility that LPG may be less rare in this part of the world than currently thought, and should definitely be considered when nephrotic syndrome is associated with suggestive kidney biopsy findings.

APOE gene variants in primary dyslipidemia

Apolipoprotein E (apoE) is a major apolipoprotein involved in lipoprotein metabolism. It is a polymorphic protein and different isoforms are associated with variations in lipid and lipoprotein levels and thus cardiovascular risk. The isoform apoE4 is associated with an increase in LDL-cholesterol levels and thus a higher cardiovascular risk compared to apoE3. Whereas, apoE2 is associated with a mild decrease in LDL-cholesterol levels. In the presence of other risk factors, apoE2 homozygotes could develop type III hyperlipoproteinemia (familial dysbetalipoproteinemia or FD), an atherogenic disorder characterized by an accumulation of remnants of triglyceride-rich lipoproteins. Several rare APOE gene variants were reported in different types of dyslipidemias including FD, familial combined hyperlipidemia (FCH), lipoprotein glomerulopathy and bona fide autosomal dominant hypercholesterolemia (ADH). ADH is characterized by elevated LDL-cholesterol levels leading to coronary heart disease, and due to molecular alterations in three main genes: LDLR, APOB and PCSK9. The identification of the APOE-p.Leu167del variant as the causative molecular element in two different ADH families, paved the way to considering APOE as a candidate gene for ADH. Due to non mendelian interacting factors, common genetic and environmental factors and perhaps epigenetics, clinical presentation of lipid disorders associated with APOE variants often strongly overlap. More studies are needed to determine the spectrum of APOE implication in each of the diseases, notably ADH, in order to improve clinical and genetic diagnosis, prognosis and patient management. The purpose of this review is to comment on these APOE variants and on the molecular and clinical overlaps between dyslipidemias.

Lipoprotein glomerulopathy induced by ApoE Kyoto mutation in ApoE-deficient mice

Background

Lipoprotein glomerulopathy (LPG) is a rare autosomal dominant kidney disease that is most commonly caused by mutations in ApoE Kyoto (p.R43C) and ApoE Sendai (p.R163P). Differences in phenotype among the various ApoE mutations have been suggested, but the pathogenic role of ApoE Kyoto has not been validated in an animal model. This study intended to establish an ApoE Kyoto murine model and to further compare the pathologic differences between ApoE Kyoto and ApoE Sendai.

Method

Male ApoE-deficient mice, 3 months of age, were divided into five groups, including the AD-ApoE Sendai, AD-ApoE Kyoto, AD-ApoE3, AD-eGFP, and ApoE (−/−) groups. The first four groups received recombinant adenovirus that contained the entire coding regions of the human ApoE Sendai and ApoE Kyoto, apoE3, and eGFP genes, respectively. Fasting blood and urine samples were collected at multiple time points. Lipid profiles and urine albumin–creatinine ratio were measured. Renal and aortic histopathologic alterations were analyzed.

Results

After virus injection, plasma human ApoE was detected and rapidly reached the maximum level at 4–6 days in the AD-ApoE Kyoto and AD-ApoE Sendai groups (17.4 ± 3.1 µg/mL vs.: 22.2 ± 4.5 µg/mL, respectively) and at 2 days in the AD-ApoE3 group (38.4 µg/mL). The serum total cholesterol decreased by 63%, 65%, and 73% in the AD-ApoE Kyoto, AD-ApoE Sendai and AD-ApoE3 groups, respectively. There were no significant changes in serum triglyceride and urinary albumin–creatinine ratio among the five groups. Typical lipoprotein thrombi with positive ApoE staining were detected in the AD-ApoE Kyoto and AD-ApoE Sendai groups. The Oil-red O-positive glomerular area tended to be higher in the AD-ApoE Kyoto group (9.2%) than in the AD-ApoE Sendai (3.9%), AD-ApoE3 (4.8%), AD-eGFP (2.9%), and ApoE (−/−) (3.6%) groups. The atherosclerotic plaque area in the aorta was lower in the group injected with various ApoE mutations than in the group without injection of ApoE mutation.

Conclusions

In this animal study, we first established an ApoE Kyoto mutation murine model and confirmed its pathogenic role in LPG. Our results suggested that LPG may be more severe with the ApoE Kyoto than with the ApoE Sendai.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02765-x.

Apolipoprotein E-related glomerular disorders

Of the glomerular disorders that occur due to apolipoprotein E (apoE) mutations, apoE2 homozygote glomerulopathy and lipoprotein glomerulopathy (LPG) have been characterized. ApoE2 homozygote glomerulopathy has been found in individuals expressing homozygous apoE2/2. This was characterized histologically by glomerulosclerosis with marked infiltration of foam cells derived from macrophages, and occasionally with non-lamellated lipoprotein thrombi. Recently, several cases of apoE Toyonaka (Ser197Cys) combined with homozygous apoE2/2 have been reported, in which non-immune membranous nephropathy-like features were observed in glomeruli. Interestingly, in these cases, apoE accumulation was identified by tandem mass spectrometry. Therefore, it is speculated that these findings may arise from apoE molecules without lipids, which result from hinge damage by apoE Toyonaka and may cross the glomerular basement membrane as small molecules. LPG is primarily associated with heterozygous apoE mutations surrounding the low-density lipoprotein-receptor binding site, and it is histologically characterized by lamellated lipoprotein thrombi that lack foam cells. Recent studies have suggested that LPG can be induced by thermodynamic destabilization, hydrophobic surface exposure, and the aggregation of apoE resulting from the incompatibility of apoE mutated residues within helical regions. Additionally, apoE5 may play a supporting role in the development of LPG and in lipid-induced kidney diseases via hyperlipoproteinemia. Thus, it is interesting that many apoE mutations contribute to characteristic glomerular disorders through various mechanisms. In particular, macrophages may uptake lipoproteins into the cytoplasm and contribute to the development of apoE2 homozygote glomerulopathy as foam cells, and their dysfunction may contribute to the accumulation of lipoproteins in the glomerulus, causing lipoprotein thrombi in LPG.

Intravascular cardiac lipoproteinosis: extrarenal manifestation of lipoprotein glomerulopathy

Intracapillary lipoprotein thrombi are a distinct histopathologic finding described in the setting of lipoprotein glomerulopathy. The disease is associated with mutations in the apolipoprotein E gene and responds well to lipid-lowering treatments. Lipoprotein glomerulopathy is thought to primarily affect the kidneys, and lipoprotein thrombi have never been described in any other organ. Herein we present the first recognized case with extrarenal manifestations in the form of intravascular cardiac lipoprotein deposition.

A novel apolipoprotein E mutation caused by a five amino acid deletion in a Chinese family with lipoprotein glomerulopathy: a case report

BACKGROUND

Lipoprotein glomerulopathy (LPG) is a rare kidney disease with a poor prognosis that is related to mutation of the apoE gene. More than 10 variants of apoE associated with LPG have currently been identified.

CASE PRESENTATION

A male and his mother presented with proteinuria during a health examination. They went to hospital for further examination. Renal biopsy was performed, and the diagnosis was lipoprotein glomerulopathy (LPG), which is a rare, inherited renal disease. Medical histories were collected from the 2 LPG patients and their family members. The patients and family members underwent a routine urine test, and their renal function, blood lipids, and lipoprotein levels were examined. Genomic DNA was extracted from the peripheral blood of 7 family members, and exon 2, exon 3 and exon 4 of apoE were amplified by polymerase chain reaction (PCR). The purified PCR products were sequenced. Sequence analysis identified a 15 bp deletion (GCGCAAGCTGCGTAA) in exon 4 of the apoE gene that results in a novel 5 amino acid deletion in apoE (143 K-147R → 0). No mutations were found in exon 2 and exon 3 of the apoE gene.

CONCLUSIONS

This family study suggests that a novel ApoE mutation (143 K-147R → 0) may be etiologically related to LPG, and other genetic or environmental factors may be associated with the occurrence of LPG.

The Novel Apolipoprotein E Mutation ApoE Chengdu (c.518T＞C, p.L173P) in a Chinese Patient with Lipoprotein Glomerulopathy

Aims: Lipoprotein glomerulopathy (LPG) is a rare inherited renal disease. Several apolipoprotein E (apoE) mutations have been reported to be related to LPG. Herein, we report a case of a LPG patient with a novel apoE mutation.

Methods: A 45-year-old Chinese female was diagnosed as LPG by renal biopsy. APOE gene was sequenced. Clinical and genetic studies were conducted.

Results: The patient presented with nephrotic syndrome and hypertension. A fasting lipid panel showed mild hyperlipidemia and elevated serum apoE (5.6 mg/dL). Renal biopsy revealed typical LPG lesions with whorled, mesh-like material in dilated glomerular capillary lumens that stained positive for Sudan III and apoE. apoE gene analysis revealed a T-to-C point mutation at amino acid 173 that caused a substitution of a proline residue for a leucine residue, which has not been reported previously. We named this mutation apoE Chengdu (c.518T> C, p.L173P). Two of five of the family members carried this mutation, including the patient's brother who was receiving hemodialysis, and her sister, whose urine protein levels were normal. All mutation carriers were heterozygotes with the apoE genotype ε3/ε3. This mutation was not found among 200 of the local people. Fenofibrate treatment for one year induced clinical improvement.

Conclusions: ApoE Chengdu (p.L173P) is a novel mutation causing LPG. This case supports the hypothesis that the substitution of proline in or near the LDL receptor-binding area contributes to the development of LPG. The detailed mechanism of action of this variant remains to be elucidated.

Five-year follow-up of a case of lipoprotein glomerulopathy with APOE Kyoto mutation

We report the case of a 34-year-old Japanese male with lipoprotein glomerulopathy (LPG). Renal biopsy showed LPG, and followed by a genetic analysis revealed a mutation in apolipoprotein E gene (APOE Kyoto; Arg25Cys). We started treatment with probucol, bezafibrate, losartan, and allopurinol. Urinary protein decreased in response to treatment but has remained at about 1.27 ± 0.71 g/gCr, and a repeat biopsy which was performed 1 year after the first biopsy showed no clear evidence of pathological remission and complication of other glomerular disease. After 5 years of follow-up after the start of treatment, renal function has almost maintained without apparent deterioration. Interestingly, the course of the urinary protein level closely paralleled his triglyceride and cholesterol levels in a long-term. This observation suggests the importance of tight control of lipid profiles as a means of renoprotection in LPG patient.

Analysis of differentially expressed novel post-translational modifications of plasma apolipoprotein E in Taiwanese females with breast cancer

APOE ε2 or ε4 alleles being used as indicators of breast cancer risk are controversial in Taiwanese females. We provide a concept for relative comparisons of post-translational modifications (PTMs) of plasma apolipoprotein E (ApoE) between normal controls and breast cancer patients to investigate the association of ApoE with breast cancer risk. APOE polymorphisms (ApoE isoforms) were not assessed in this study. The relative modification ratio (%) of 15 targeted and 21 modified peptides were evaluated by 1D SDS-PAGE, in-gel digestion, and label-free nano-LC/MS to compare normal controls with breast cancer patients. Plasma levels of the ApoE protein did not significantly differ between normal controls and breast cancer patients. Eleven sites with novel PTMs were identified from 7 pairs of differentially expressed targeted and modified peptides according to the relative modification ratio including methylation at the E3 (↑1.45-fold), E7 (↑1.45-fold), E11 (↑1.19-fold), E77 (↑2.02-fold), E87 (↑2.02-fold), and Q98 (↑1.62-fold) residues; dimethylation at the Q187 (↑1.44-fold) residue; dihydroxylation at the R92 (↑1.25-fold), K95 (↑1.25-fold), and R103 (↑1.25-fold) residues; and glycosylation at the S129 (↑1.14-fold) residue. The clustered methylation and dihydroxylation of plasma ApoE proteins may play a role in breast cancer.

Apolipoprotein e mutation and double filtration plasmapheresis therapy on a new Chinese patient with lipoprotein glomerulopathy

BACKGROUND/AIMS

Lipoprotein glomerulopathy (LPG) is a rare hereditary disease. In this study, we investigated the apoE mutation and the role of double filtration plasmapheresis therapy (DFPP) on a new Chinese patient with LPG.

METHODS

Renal biopsy was performed on this patient to allow a definitive diagnosis. The mutations in the coding sequence of apoE and the hereditary pedigree of this patient were investigated by DNA sequencing. The patient was treated with DFPP, and clinical parameters before and after DFPP were compared.

RESULTS

Two missense mutations were found in this patient: Cys112Arg and Arg25Cys. Arg25Cys was previously designated as APOE Kyoto. Family genotyping showed that Cys112Arg and Arg25Cys mutation were transmitted through his father and his mother, respectively. The patient's parents are healthy so far to date. Possibly there was a dose effect on apoE mutation induced LPG. Furthermore, DFPP treatment was first used on this patient and led to dramatic changes: Proteinuria and apo E values declined, and hemoglobin level increased significantly.

CONCLUSION

APOE Kyoto mutation was found in a new Chinese patient with LPG, accompanied by Cys112Arg. More cases and further functional experiments are needed to investigate the role of these two mutations together in LPG. DFPP is an effective therapeutic modality for improving NS in patients with LPG.

Apolipoprotein E mutations: a comparison between lipoprotein glomerulopathy and type III hyperlipoproteinemia

Apolipoprotein E (ApoE) serves as a ligand for the low-density lipoprotein (LDL) receptor and cell surface receptors of the LDL receptor gene family. More than 10 different causative apoE mutations associated with lipoprotein glomerulopathy (LPG) have been reported. ApoE polymorphisms including three common phenotypes (E2, E3, E4), and a variety of rare mutations can affect blood cholesterol and triglyceride levels. The N-terminal domain of apoE is folded into a four-helix bundle of amphipathic α-helices, and contains the receptor-binding domain in which most apoE mutations that cause LPG or dominant mode of type III hyperlipoproteinemia (HL) are located. No single apoE mutation has been reported that causes both LPG and the dominant mode of type III HL.

Dysbetalipoproteinaemia: a mixed hyperlipidaemia of remnant lipoproteins due to mutations in apolipoprotein E

Atherosclerosis is strongly associated with dyslipoproteinaemia, and especially with increasing concentrations of low-density lipoprotein and decreasing concentrations of high-density lipoproteins. Its association with increasing concentrations of plasma triglyceride is less clear but, within the mixed hyperlipidaemias, dysbetalipoproteinaemia (Fredrickson type III hyperlipidaemia) has been identified as a very atherogenic entity associated with both premature ischaemic heart disease and peripheral arterial disease. Dysbetalipoproteinaemia is characterized by the accumulation of remnants of chylomicrons and of very low-density lipoproteins. The onset occurs after childhood and usually requires an additional metabolic stressor. In women, onset is typically delayed until menopause. Clinical manifestations may vary from no physical signs to severe cutaneous and tendinous xanthomata, atherosclerosis of coronary and peripheral arteries, and pancreatitis when severe hypertriglyceridaemia is present. Rarely, mutations in apolipoprotein E are associated with lipoprotein glomerulopathy, a condition characterized by progressive proteinuria and renal failure with varying degrees of plasma remnant accumulation. Interestingly, predisposing genetic causes paradoxically result in lower than average cholesterol concentration for most affected persons, but severe dyslipidaemia develops in a minority of patients. The disorder stems from dysfunctional apolipoprotein E in which mutations result in impaired binding to low-density lipoprotein (LDL) receptors and/or heparin sulphate proteoglycans. Apolipoprotein E deficiency may cause a similar phenotype. Making a diagnosis of dysbetalipoproteinaemia aids in assessing cardiovascular risk correctly and allows for genetic counseling. However, the diagnostic work-up may present some challenges. Diagnosis of dysbetalipoproteinaemia should be considered in mixed hyperlipidaemias for which the apolipoprotein B concentration is relatively low in relation to the total cholesterol concentration or when there is significant disparity between the calculated LDL and directly measured LDL cholesterol concentrations. Genetic tests are informative in predicting the risk of developing the disease phenotype and are diagnostic only in the context of hyperlipidaemia. Specialised lipoprotein studies in reference laboratory centres can also assist in diagnosis. Fibrates and statins, or even combination treatment, may be required to control the dyslipidaemia.

A possible structural basis behind the pathogenic role of apolipoprotein E hereditary mutations associated with lipoprotein glomerulopathy

Single amino acid mutations in apolipoprotein E (apoE) have been associated with the development of the rare kidney disease lipoprotein glomerulopathy (LPG). Although the genetic linkage to disease development is well established, the mechanism of pathogenesis is largely unknown, limiting therapeutic insight. Here, we summarize current knowledge in the field and focus on the possible effects of LPG-associated mutations on the structure of apoE. Recent findings have suggested that mutation-induced folding perturbations in apoE lead to structural destabilization and aggregation, effects that may underlie lipoprotein thrombi accumulation in the glomerulus, a hallmark of LPG. The recognition that structural destabilization may underlie the association between apoE mutations and LPG can be key for development of new innovative treatments for this rare disease.

A founder haplotype of APOE-Sendai mutation associated with lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a hereditary disease characterized by lipoprotein thrombi in the glomerulus, hyperlipoproteinemia, and a marked increase in serum apolipoprotein E (APOE). More than 12 APOE mutations have been identified as causes of LPG, and APOE-Sendai (Arg145Pro) mutation was frequently detected in patients from the eastern part of Japan including Yamagata prefecture. Recently, effective therapy with intensive lipid-lowering agents was established, and epidemiologic data are required for early diagnosis. We determined the haplotype structure of APOE-Sendai in 13 patients from 9 unrelated families with LPG, and found that the haplotype of all APOE-Sendai mutations was identical, suggesting that APOE-Sendai mutation is common in Japanese patients probably through a founder effect. We also studied the gene frequency of APOE-Sendai in 2023 control subjects and 418 patients receiving hemodialysis in Yamagata prefecture using the TaqMan method, but did not identify any subjects carrying the mutation, indicating that it is very rare in the general population even in the eastern part of Japan. In addition to APOE mutation, other genetic and/or epigenetic factors are considered to be involved in the pathogenesis of LPG because of its low penetrance. The patients did not have a common haplotype of the counterpart APOE allele, and some patients had the same haplotype of the counterpart APOE allele as the asymptomatic carriers. These results suggest that the counterpart APOE allele is not likely associated with the onset of LPG. Further study is required to clarify the pathogenesis of LPG.

Thermodynamic and structural destabilization of apoE3 by hereditary mutations associated with the development of lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a dominant inherited kidney disorder characterized by lipoprotein thrombi in glomerular capillaries. Single-amino-acid mutations in apoE have been associated with the development of the disease, although the mechanism is unknown. In an effort to gain mechanistic insight linking the presence of such mutations and the development of LPG, we evaluated the effects of three of the most common apoE3 variants associated with this disease, namely R145P(Sendai), R147P(Chicago), and R158P(Osaka or Kurashiki), on the structural and conformational integrity of the protein. All three variants were found to have significantly reduced helical content, to expose a larger portion of hydrophobic surface to the solvent, and to be significantly thermodynamically destabilized, often lacking functionally relevant unfolding intermediates. Furthermore, all variants were aggregation prone and had enhanced sensitivity to protease digestion. Finally, although the variants were able to form discoidal lipoprotein particles, discrete subpopulations of poorly formed or aberrant particles were evident. Furthermore, these lipoprotein particles were thermodynamically destabilized and aggregation prone. Overall, our data suggest that these mutations induce a generalized unfolding of the N-terminal domain of apoE3 toward a molten-globule-like structure. ApoE3 N-terminal domain unfolding due to mutation may constitute a common mechanism underlying the protein's association with the pathogenesis of LPG.