Guidance for the diagnosis and treatment of hypolipidemia disorders

Reducing LDL-Cholesterol to Very Low Levels: Sailing Between Established Benefits and Potential Risks

In view of the growing evidence supporting more marked reductions of low-density lipoprotein cholesterol (LDL-C), according to the concept of "the lower is better" and with the availability of powerful and well tolerated lipid-lowering drugs, physicians are facing today with the clinical management of patients with very low LDL-C levels. The fear of potential risks linked to extreme reductions of LDL-C down to very low levels may lead to the de-escalation of treatments with consequent paradoxical unfavorable consequences due to the exposure to a higher cardiovascular risk. The aim of this review is to point out evidence of very low LDL-C clinical impact, with a focus on potential adverse effects. Research on cholesterol homeostasis has identified complex mechanisms which guarantee cell functions even when circulating cholesterol levels are very low. The almost complete self-sufficiency of the human body in terms of cholesterol needs is confirmed by evidence derived from genetically determined models with very low LDL-C levels. Studies on the potential harm of lowering LDL-C to very low concentrations do not confirm an increased risk of cancer or neurodegenerative disease attributable to lipid-lowering treatments, whereas evidence suggests a potential benefit in these settings. A potential increased risk of hemorrhagic stroke has been reported, suggesting tight monitoring and control of blood pressure should be implemented in patients with very low LDL-C levels. With regard to statin treatment, a dose-dependent increased risk of newly diagnosed diabetes has been reported. This adverse effect has not been found with more recently approved lipid-lowering drugs.

Pathological features of non-alcoholic steatohepatitis in a pediatric patient with heterozygous familial hypobetalipoproteinemia: A case report

BACKGROUND

Heterozygous familial hypobetalipoproteinemia (FHBL) is a semi-autosomal disorder that is caused mainly by an APOB variant. It is usually asymptomatic and rarely leads to non-alcoholic steatohepatitis (NASH).

CASE SUMMARY

A 12-year-old boy was referred to our hospital after prolonged elevation of liver enzymes was observed during health checkups in Kagawa Prefecture. Abdominal ultrasound showed a bright liver, and laboratory investigations revealed low low-density lipoprotein cholesterol and apolipoprotein B protein levels. His family history included fatty liver and hypolipidemia in his father, which led to a clinical diagnosis of FHBL. A liver biopsy was performed on suspicion of liver fibrosis based on biomarkers. The liver tissue showed fatty steatosis, inflammation, hepatocyte ballooning, and fibrosis, indicating NASH. Genetic testing detected the APOB variant, and the patient was treated successfully with vitamin E.

CONCLUSION

It is important to assess family history and liver dysfunction severity in non-obese patients with hypolipidemia and fatty liver.

Clinical and biochemical spectrum of APOB-related hypobetalipoproteinemia: Insights from a retrospective cohort study

BACKGROUND

APOB-related familial hypobetalipoproteinemia (APOB-FHBL), the most common form of primary hypobetalipoproteinemia, often leaves heterozygous patients asymptomatic. This study aims to provide updated insights into the complications observed in heterozygous and homozygous APOB-FHBL patients.

METHODS

A retrospective analysis was conducted on 15 patients (53.3% female) from 7 families diagnosed with FHBL and followed in a metabolic clinic. Demographic, laboratory, clinical, and genetic data were reviewed.

RESULTS

Patients were followed for an average of 4.5 ± 4.1 years. The median levels were as follows: low-density lipoprotein cholesterol (LDL-C; 25.7 ± 10.5 mg/dL), apolipoprotein B (ApoB; 0.3 ± 0.1 g/L), aspartate aminotransferase (AST; 40.1 ± 22.5 U/L), alanine aminotransferase (ALT; 43.0 ± 38.3 U/L), and alpha feto-protein (AFP; 1.3 ± 0.7 ng/mL). Elevated AST and ALT levels were observed in 20.0% and 26.7% of cases, respectively. Vitamin E deficiency was identified in 26.7%, vitamin A deficiency in 13.3%, and vitamin D insufficiency in 66.7% of cases. Liver ultrasonography revealed hepatosteatosis in 73.3% of patients. Additionally, the study identified 5 novel APOB gene variants. Among the families, 3 had members who died due to complications related to viral infections (COVID-19, hepatitis B virus) or hepatocellular carcinoma (HCC) resulting from chronic liver disease.

CONCLUSION

Patients with elevated transaminase levels or hepatosteatosis should undergo a lipid profile assessment. LDL-C levels below 50 mg/dL require further evaluation, including ApoB and fat-soluble vitamin levels. Monoallelic APOB variants are linked to poor outcomes due to deficiencies in vitamins A, E, and D, as well as an increased risk of HCC. Early recognition and regular monitoring are essential for the effective management of APOB-FHBL patients.

Prevalence, genetic variants, and clinical implications of hypocholesterolemia in children

BACKGROUND AND AIMS

In contrast to extensively studied hypercholesterolemia, knowledge of hypocholesterolemia is limited. This study aims to assess the prevalence, clinical characteristics, and genetics of children and adolescents with hypocholesterolemia.

METHODS

This national prospective cross-sectional cohort study was part of Slovenia's universal opt-out cholesterol screening program. The first part assessed hypocholesterolemia prevalence among 3538 children aged 5 years, randomly selected at the mandatory check-up. The second part included analysis of demographic and clinical data and genetic testing of 71 individuals with suspected hypocholesterolemia (total cholesterol [TC] < 3.0 mmol/L [116.0 mg/dL]) referred to the Lipid Clinic of University Children's Hospital Ljubljana.

RESULTS

The prevalence of hypocholesterolemia among 3538 children was 2.66 % (95 % CI: 2.13-3.19 %). Among the 71 genetically tested individuals with suspected hypocholesterolemia, those with pathogenic variants had lower TC (2.58 ± 0.44 mmol/L vs. 2.85 ± 0.42 mmol/L [99.77 ± 17.02 mg/dL vs. 110.20 ± 16.24 mg/dL]; p = 0.037) and low-density lipoprotein cholesterol (1.00 ± 0.40 mmol/L vs. 1.33 ± 0.40 mmol/L [38.67 ± 15.47 mg/dL vs. 51.43 ± 15.47 mg/dL]; p = 0.014) compared to those without such variants. Genetic testing identified pathogenic alterations in 15 subjects, including 4 novel loss-of-function variants in the APOB gene. All but one subject were asymptomatic.

CONCLUSIONS

This study provides new clinical and genetic insights into hypocholesterolemia. Asymptomatic patients with hypocholesterolemia may not require further evaluation, but additional research is needed to understand hypocholesterolemia better.

A novel mutation, Ile344Asn, in microsomal triglyceride transfer protein abolishes binding to protein disulfide isomerase

Microsomal triglyceride transfer protein (MTP) plays crucial roles in the assembly and secretion of apolipoprotein B-containing lipoproteins and loss of function MTP variants are associated with abetalipoproteinemia, a disease characterized by the absence of these lipoproteins. MTP is a heterodimeric protein of two subunits, MTP and protein disulfide isomerase (PDI). In this study, we report a proband with abetalipoproteinemia who was monitored annually for 10 years in her third decade and had very low plasma lipids and undetectable apoB-containing lipoproteins. Genetic testing revealed biallelic variants in the MTTP gene. She has a well-documented nonsense mutation Gly865∗ that does not interact with the PDI subunit. She also has a novel missense MTP mutation, Ile344Asn. We show that this mutation abrogates lipid transfer activity in MTP and does not support apolipoprotein B secretion. This residue is present in the central α-helical domain of MTP and the substitution of Ile with Asn at this position disrupts interactions between MTP and PDI subunits. Ile344 is away from the known MTP:PDI interacting sites identified in the crystal structure of MTP suggesting that MTP:PDI interactions are more dynamic than previously envisioned. Identification of more missense mutations will enhance our understanding of the structure-function of MTP and the role of critical residues in these interactions between the two subunits. This knowledge may guide us in developing novel treatment modalities to reduce plasma lipids and atherosclerosis.

Abetalipoproteinemia with angioid streaks, choroidal neovascularization, atrophy, and extracellular deposits revealed by multimodal retinal imaging

PURPOSE

Abetalipoproteinemia (ABL, MIM 200,100) is a rare autosomal recessive disorder caused by nonfunctional microsomal triglyceride transfer protein leading to absence of apolipoprotein B-containing lipoproteins in plasma and a retinitis pigmentosa-like fundus. The MTTP gene is expressed in retinal pigment epithelium (RPE) and ganglion cells of the human retina. Understanding ABL pathophysiology would benefit from new cellular-level clinical imaging of affected retinas.

METHODS

We report multimodal retinal imaging in two patients with ABL. Case 1 (67-year-old woman) exhibited a bilateral decline of vision due to choroidal neovascularization (CNV) associated with angioid streaks and calcified Bruch membrane. Optical coherence tomography were consistent with basal laminar deposits and subretinal drusenoid deposits (SDD).

RESULTS

Case 2 (46-year-old woman) exhibited unusual hyperpigmentation at the right fovea with count-fingers vision and a relatively unremarkable left fundus with 20/30 vision. The left eye exhibited the presence of nodular drusen and SDD and the absence of macular xanthophyll pigments.

CONCLUSION

We propose that mutated MTTP within the retina may contribute to ABL retinopathy in addition to systemic deficiencies of fat-soluble vitamins. This concept is supported by a new mouse model with RPE-specific MTTP deficiency and a retinal degeneration phenotype. The observed range of human pathology, including angioid streaks, underscores the need for continued monitoring in adulthood, especially for CNV, a treatable condition.

Low LDL-C: Is It all Good News?

PURPOSE OF REVIEW

This review presents the risks and benefits of very low LDL cholesterol and the safety of using lipid-lowering therapy to achieve these levels.

RECENT FINDINGS

A growing body of literature suggests that lower LDL cholesterol levels are associated with a reduced risk of cardiovascular disease. Further, achieving these levels with pharmaceuticals is remarkably safe. Although statins may slightly increase the risk of diabetes mellitus and hemorrhagic stroke, the benefits outweigh the risks. While recommendations from professional societies are increasingly aggressive, additional risk reduction could be achieved by setting more even ambitious LDL cholesterol goals.

A New Case of Abetalipoproteinemia Caused by Novel Compound Heterozygote Mutations in the MTTP Gene without Fat or Vitamin Malabsorption

Abetalipoproteinemia (ABL) is a rare disease characterized by extremely low apolipoprotein B (apoB)-containing lipoprotein levels, dietary fat, and fat-soluble vitamin malabsorption, leading to gastrointestinal, neuromuscular, and ophthalmological symptoms. We herein report a case of ABL with novel compound heterozygous mutations in the microsomal triglyceride transfer protein gene (c.1686_1687del [p.Ser563TyrfsTer10] and c.1862T>C [p.Ile621Thr]), identified via panel sequencing. Although the patient had extremely reduced low-density lipoprotein cholesterol levels and a fatty liver, he did not exhibit other typical complications. Furthermore, unlike typical ABL, this patient had a preserved apoB-48 secretion and increased concentrations of high-density lipoprotein cholesterol, which may account for the normal serum fat-soluble vitamin levels.

A Family with Familial Hypobetalipoproteinemia Caused by a c.1468C>T in APOB

We herein report the first family of Japanese individuals with familial hypobetalipoproteinemia caused by the c.1468C>T mutation in apolipoprotein B (APOB). A 13-year-old boy with extremely low levels of low-density lipoprotein (LDL) cholesterol (24 mg/dL) was referred to our hospital. The patient had no secondary causes of hypobetalipoproteinemia. His father and grandmother also exhibited low LDL cholesterol levels. A genetic analysis confirmed that they all had this variant in APOB (c.1468C>T). None of the patients exhibited atherosclerotic cardiovascular diseases or any other complications associated with low LDL cholesterol levels, including fatty liver, neurocognitive disorders, and cerebral hemorrhaging.

Exploring Plasma Coenzyme Q10 Status in Paediatric Dyslipidaemia

Coenzyme Q10 (CoQ) is a ubiquitous lipid with different biological functions. In blood, there is a close relationship between CoQ status and cholesterol, which strongly supports the study of both molecules simultaneously. The objective of this study was to evaluate plasma CoQ, lipoprotein concentrations and CoQ/Chol ratio in a cohort of paediatric patients with different types of dyslipidaemias. A total of 60 paediatric patients were recruited (age range: 7 months-18 years), including 52 with different types of hypercholesterolemia, 2 with isolated hypertriglyceridemia and 6 with hypobetalipoproteinemia. Plasma CoQ was analysed by HPLC with electrochemical detection, and lipoprotein and cholesterol concentrations by standard automated methods. The lowest CoQ values were detected in patients with hypobetalipoproteinemia and in two cases of liver cirrhosis. Mean CoQ values were significantly higher in hypercholesterolemic patients compared to controls (average values 1.07 µmol/L and 0.63 µmol/L) while the CoQ/cholesterol ratio did not show differences (170 vs. 163, respectively). Mean CoQ values were significantly lower in the group of patients with hypobetalipoproteinemia compared to controls (mean CoQ values of 0.22 µmol/L vs. 0.63 µmol/L, respectively), while those of CoQ/cholesterol did not show differences. Pearson's correlation test showed a positive correlation between the CoQ and cholesterol values (r = 0.565, p < 0.001) and between the CoQ and the LDL cholesterol values (r = 0.610, p < 0.001). Our results suggest that it is advisable to analyse plasma CoQ and cholesterol concentrations in patients with hypobetalipoproteinemia and hypercholesterolemia associated with liver damage.

Scientific opinion on the tolerable upper intake level for vitamin E

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver a scientific opinion on the revision of the tolerable upper intake level (UL) for vitamin E. As α-tocopherol is recognised as the only essential form of vitamin E, the Panel restricted its evaluation to α-tocopherol. Systematic reviews of the literature were conducted to assess evidence on priority adverse health effects of excess intake of vitamin E, namely risk of impaired coagulation and bleeding, cardiovascular disease and prostate cancer. The effect on blood clotting and associated increased risk of bleeding is considered as the critical effect to establish an UL for vitamin E. No new evidence has been published that could improve the characterisation of a dose-response. The ULs for vitamin E from all dietary sources, which were previously established by the Scientific Committee on Food, are retained for all population groups, i.e. 300 mg/day for adults, including pregnant and lactating women, 100 mg/day for children aged 1-3 years, 120 mg/day for 4-6 years, 160 mg/day for 7-10 years, 220 mg/day for 11-14 years and 260 mg/day for 15-17 years. A UL of 50 mg/day is established for infants aged 4-6 months and a UL of 60 mg/day for infants aged 7-11 months. ULs apply to all stereoisomeric forms of α-tocopherol. ULs do not apply to individuals receiving anticoagulant or antiplatelet medications (e.g. aspirin), to patients on secondary prevention for CVD or to patients with vitamin K malabsorption syndromes. It is unlikely that the ULs for vitamin E are exceeded in European populations, except for regular users of food supplements containing high doses of vitamin E.

High carrier frequency for abetalipoproteinemia and evidence of a founder variant in a French-Canadian population

Abetalipoproteinemia (ABL) is a rare recessive genetic disease caused by bi-allelic pathogenic variants in the microsomal triglyceride transfer protein (MTTP) gene. This disease is characterized by a deficiency in the secretion of apolipoprotein B-containing lipoproteins. Patients with ABL present with neurological, hematological, and gastrointestinal symptoms due to fat malabsorption and a deficiency in liposoluble vitamins. In this report, we present a total of four ABL cases, including three new cases, all originating from the same French-Canadian founder population in Saguenay-Lac-Saint-Jean, Québec, Canada. These individuals are homozygous for the same pathogenic variant in the MTTP gene (c.419dup, p.Asn140Lysfs*2). We found that this variant is more common than anticipated in this population, with an estimated carrier frequency of 1:203. Early diagnosis is essential to initiate treatment known to prevent complications associated with ABL. Population carrier screening or newborn screening for ABL should be considered in this French-Canadian founder population.

Current Diagnosis and Management of Familial Hypobetalipoproteinemia 1

Familial hypobetalipoproteinemia (FHBL) 1 is a rare genetic disorder with an autosomal codominant mode of inheritance and is caused by defects in the apolipoprotein (apo) B (APOB) gene that disable lipoprotein formation. ApoB proteins are required for the formation of very low-density lipoproteins (VLDLs), chylomicrons, and their metabolites. VLDLs transport cholesterol and triglycerides from the liver to the peripheral tissues, whereas chylomicrons transport absorbed lipids and fat-soluble vitamins from the intestine. Homozygous or compound heterozygotes of FHBL1 (HoFHBL1) are extremely rare, and defects in APOB impair VLDL and chylomicron secretion, which result in marked hypolipidemia with malabsorption of fat and fat-soluble vitamins, leading to various complications such as growth disorders, acanthocytosis, retinitis pigmentosa, and neuropathy. Heterozygotes of FHBL1 are relatively common and are generally asymptomatic, except for moderate hypolipidemia and possible hepatic steatosis. If left untreated, HoFHBL1 can cause severe complications and disabilities that are pathologically and phenotypically similar to abetalipoproteinemia (ABL) (an autosomal recessive disorder) caused by mutations in the microsomal triglyceride transfer protein (MTTP) gene. Although HoFHBL1 and ABL cannot be distinguished from the clinical manifestations and laboratory findings of the proband, moderate hypolipidemia in first-degree relatives may help diagnose HoFHBL1. There is currently no specific treatment for HoFHBL1. Palliative therapy including high-dose fat-soluble vitamin supplementation may prevent or delay complications. Registry research on HoFHBL1 is currently ongoing to better understand the disease burden and unmet needs of this life-threatening disease with few therapeutic options.

Diet management in congenital diarrheas and enteropathies - general concepts and disease-specific approach, a narrative review

Congenital diarrheas and enteropathies (CODE) are a group of rare, heterogenous, monogenic disorders that lead to chronic diarrhea in infancy. Definitive treatment is rarely available, and supportive treatment is the mainstay. Nutritional management in the form of either specialized formulas, restrictive diet, or parenteral nutrition support in CODE with poor enteral tolerance is the cornerstone of CODE treatment and long-term growth. The evidence to support the use of specific diet regimens and nutritional approaches in most CODE disorders is limited due to the rarity of these diseases and the scant published clinical experience. The goal of this review was to create a comprehensive guide for nutritional management in CODE, based on the currently available literature, disease mechanism, and the PediCODE group experience. Enteral diet management in CODE can be divided into 3 distinct conceptual frameworks: nutrient elimination, nutrient supplementation, and generalized nutrient restriction. Response to nutrient elimination or supplementation can lead to resolution or significant improvement in the chronic diarrhea of CODE and resumption of normal growth. This pattern can be seen in CODE due to carbohydrate malabsorption, defects in fat absorption, and occasionally in electrolyte transport defects. In contrast, general diet restriction is mainly supportive. However, occasionally it allows parenteral nutrition weaning or reduction over time, mainly in enteroendocrine defects and rarely in epithelial trafficking and polarity defects. Further research is required to better elucidate the role of diet in the treatment of CODE and the appropriate diet management for each disease.

Hypolipidemia due to Familial Hypobetalipoproteinemia in Adolescents

Background/Objective

Individuals with heterozygous familial hypobetalipoproteinemia (h-FHBL) due to loss-of-function mutation in the apolipoprotein B gene are typically asymptomatic with mild liver dysfunction, which is often detected incidentally. About 5% to 10% of those with h-FHBL develop steatohepatitis which occasionally progress to cirrhosis especially in the presence of alcohol use, excess calorie consumption, or liver injury. We report 3 patients with hypobetalipoproteinemia, 2 with confirmed h-FHBL, and 1 with suspected h-FHBL.

Case Report

Three asymptomatic adolescents presented with low lipid levels detected on screening laboratory studies. Patient 1, a 13 6/12-year-old male and patient 2, a 15 9/12-year-old female, were siblings. Patient 3 was a 12 6/12-year-old female. All had total cholesterol ranging from 61 to 87 mg/dL, low-density lipoprotein cholesterol 10 to 28 mg/dL, and triglycerides 19 to 36 mg/dL. Aspartate transaminase and alanine transaminase levels were normal in patients 1 and 3 and were elevated in patient 2. Liver ultrasounds of patients 2 and 3 showed hepatic steatosis. Molecular testing identified pathogenic variant of apolipoprotein B gene in patients 1 and 2, c.133C>T(p.Arg.45Ter) confirming the diagnosis of h-FHBL.

Discussion

More studies are needed in children with h-FHBL and other forms of hypobetalipoproteinemia to improve awareness of these disorders and to develop guidelines for monitoring and risk reduction in affected patients.

Conclusion

Health care providers should be aware that persistent hypolipidemia may indicate h-FHBL, which can be a risk factor for liver dysfunction. Youth with h-FHBL should be counseled about lifestyle modifications and screened for the development of metabolic dysfunction-associated steatotic liver disease.

Primary hypocholesterolemia is associated with an increased risk of hepatic complications in the general population

BACKGROUND & AIMS

Beyond cardiovascular disease protection, the health consequences of very low concentrations of low-density lipoprotein-cholesterol (LDL-C) remain a matter of debate. In primary hypobetalipoproteinemia (HBL), liver steatosis and cirrhosis have occasionally been reported. Here, we aimed to investigate the association between HBL and the risk of hepatic complications (cirrhosis complications and/or primary liver cancer) in the general population.

METHODS

A cohort study was conducted in the French population-based cohort CONSTANCES. Participants with primary HBL (LDL-C <5th percentile for age and sex, [HBL]) were compared with those with normal LDL-C concentrations (40th-60th percentile, [Control]). Participants on lipid-lowering therapies were excluded. For hepatic complications, follow-up events were compared by calculating the incidence density ratio (IDR). The same analyses were replicated in the UK Biobank (UKBB) cohort.

RESULTS

In the CONSTANCES and UKBB cohorts, 34,653 and 94,666 patients were analyzed, with median ages of 45 and 56 years, mean LDL-C concentrations (HBL vs. control) of 71 vs. 128 mg/dl and 86 vs. 142 mg/dl, and mean follow-up durations of 5.0 and 11.5 years, respectively. The HBL group presented a higher incidence of hepatic complications than the control group: 0.32/ vs. 0.07/1,000 person-years (IDR = 4.50, 95% CI 1.91-10.6) in CONSTANCES, and 0.69/ vs. 0.21/1,000 person-years (IDR = 3.27, 95% CI 2.63-4.06) in the UKBB. This risk proved to be independent of classic risk factors for liver disease (obesity, alcohol consumption, diabetes, viral hepatitis), including in a 5-year landmark analysis excluding early events. Sensitivity analyses based on apoliprotein-B levels (instead of LDL-C levels) or genetically defined HBL showed similar results.

CONCLUSIONS

HBL is associated with a markedly increased risk of hepatic complications. HBL must be considered as a substantial independent risk factor for liver diseases which justifies specific prevention and screening.

IMPACT AND IMPLICATIONS

Hypobetalipoproteinemia (HBL) is a lipid disorder characterized by permanent, inherited low levels (below the 5th percentile) of low-density lipoprotein-cholesterol. While HBL is associated with a lower risk of cardiovascular events, some studies suggest that it may be associated with a potential risk of hepatic steatosis and hepatic complications. Here, we studied the association between HBL and hepatic complications (defined as cirrhosis complications and/or primary liver cancer) in two populations of several hundred thousand people, both in France (CONSTANCES cohort) and the United Kingdom (UKBB). The results show that HBL is associated with a significant and independent excess risk of hepatic complications, including primary liver cancer. Thus, in people with HBL, the value of regular liver monitoring must be studied.

Chylomicron retention disease: a rare aetiology of failure to thrive

The aetiology of failure to thrive (FTT) in children is broad, of which some conditions are extremely rare. It is important to consider these rarer conditions, especially in the setting of other concerning signs/symptoms or when there is no improvement with conventional treatment. In this case report we highlight such a rare condition-chylomicron retention disease (CRD) as an aetiology of FTT. CRD often presents with non-specific symptoms, resulting in delayed diagnosis which is established by genetic workup and histology from small intestinal biopsies. Despite being rare, CRD needs to be considered as one of the differential diagnoses after ruling out the more common causes of FTT.

Transitional Medicine of Intractable Primary Dyslipidemias in Japan

Transitional medicine refers to the seamless continuity of medical care for patients with childhood-onset diseases as they grow into adulthood. The transition of care must be seamless in medical treatment as the patients grow and in other medical aids such as subsidies for medical expenses in the health care system. Inappropriate transitional care, either medical or social, directly causes poorer prognosis for many early-onset diseases, including primary dyslipidemia caused by genetic abnormalities. Many primary dyslipidemias are designated as intractable diseases in the Japanese health care system for specific medical aids, as having no curative treatment and requiring enormous treatment costs for lipid management and prevention of complications. However, there are problems in transitional medicine for primary dyslipidemia in Japan. As for the medical treatment system, the diagnosis rate remains low due to the shortage of specialists, their insufficient link with generalists and other field specialists, and poor linkage between pediatricians and physicians for adults. In the medical care system, there is a mismatch of diagnostic criteria of primary dyslipidemias between children and adults for medical care expense subsidization, as between The Program for the Specific Pediatric Chronic Diseases and the Program for Designated Adult Intractable Diseases. This could lead some patients subsidized in their childhood to no longer be under the coverage of the aids after transition. This review intends to describe these issues in transitional medicine of primary dyslipidemia in Japan as a part of the efforts to resolve the problems by the Committee on Primary Dyslipidemia under the Research Program on Rare and Intractable Disease of the Ministry of Health, Labour and Welfare of Japan.

The first Japanese case with familial combined hypolipidemia without any complications caused by loss-of function variants in ANGPTL3: Case report

Familial combined hypolipidemia, previously known as Familial hypobetalipoproteinemia 2 (FHBL2) is considered as an extremely rare recessive disease. Here, we present the case of familial combined hypolipidemia with homozygous loss-of function (LOF) variants in angiopoietin-like protein 3 (ANGPTL3) ((NM_014495.4) c.439_442del (p.Thr146_Asn147insTer)) using panel sequencing (46 yr male whose LDL cholesterol = 34 mg/dL). The serum level of ANGPTL3 was quite low (undetectable). Despite of extreme decreasing LDL cholesterol, this case did not have any complications as hypobetalipidemia (HBL), such as steatorrhea vomiting, hematological, neuromuscular, or ophthalmological symptoms. In addition, we did not find any systemic atherosclerosis in his carotid arteries and in coronary arteries. Based on the findings suggest that inhibition of ANGPTL3 effectively reduce LDL cholesterol without any apparent side effects, although it is still unclear if he will suffer any disadvantages because of this situation in the future.

Microsomal triglyceride transfer protein is necessary to maintain lipid homeostasis and retinal function

Lipid processing by the retinal pigment epithelium (RPE) is necessary to maintain retinal health and function. Dysregulation of retinal lipid homeostasis due to normal aging or age-related disease triggers lipid accumulation within the RPE, on Bruch's membrane (BrM), and in the subretinal space. In its role as a hub for lipid trafficking into and out of the neural retina, the RPE packages a significant amount of lipid into lipid droplets for storage and into apolipoprotein B (APOB)-containing lipoproteins (Blps) for export. Microsomal triglyceride transfer protein (MTP), encoded by the MTTP gene, is essential for Blp assembly. Herein we test the hypothesis that MTP expression in the RPE is essential to maintain lipid balance and retinal function using the newly generated RPEΔMttp mouse model. Using non-invasive ocular imaging, electroretinography, and histochemical and biochemical analyses we show that genetic depletion of Mttp from the RPE results in intracellular lipid accumulation, increased photoreceptor-associated cholesterol deposits, and photoreceptor cell death, and loss of rod but not cone function. RPE-specific reduction in Mttp had no significant effect on plasma lipids and lipoproteins. While APOB was decreased in the RPE, most ocular retinoids remained unchanged, with the exception of the storage form of retinoid, retinyl ester. Thus suggesting that RPE MTP is critical for Blp synthesis and assembly but is not directly involved in plasma lipoprotein metabolism. These studies demonstrate that RPE-specific MTP expression is necessary to establish and maintain retinal lipid homeostasis and visual function.

Bulky hydrophobic side chains in the β1-sandwich of microsomal triglyceride transfer protein are critical for the transfer of both triglycerides and phospholipids

Hyperlipidemia predisposes individuals to cardiometabolic diseases, the most common cause of global mortality. Microsomal triglyceride transfer protein (MTP) transfers multiple lipids and is essential for the assembly of apolipoprotein B-containing lipoproteins. MTP inhibition lowers plasma lipids but causes lipid retention in the liver and intestine. Previous studies suggested two lipid transfer domains in MTP and that specific inhibition of triglyceride (TG) and not phospholipid (PL) transfer can lower plasma lipids without significant tissue lipid accumulation. However, how MTP transfers different lipids and the domains involved in these activities are unknown. Here, we tested a hypothesis that two different β-sandwich domains in MTP transfer TG and PL. Mutagenesis of charged amino acids in β2-sandwich had no effect on PL transfer activity indicating that they are not critical. In contrast, amino acids with bulky hydrophobic side chains in β1-sandwich were critical for both TG and PL transfer activities. Substitutions of these residues with smaller hydrophobic side chains or positive charges reduced, whereas negatively charged side chains severely attenuated MTP lipid transfer activities. These studies point to a common lipid transfer domain for TG and PL in MTP that is enriched with bulky hydrophobic amino acids. Furthermore, we observed a strong correlation in different MTP mutants with respect to loss of both the lipid transfer activities, again implicating a common binding site for TG and PL in MTP. We propose that targeting of areas other than the identified common lipid transfer domain might reduce plasma lipids without causing cellular lipid retention.

Carotenoids in familial hypobetalipoproteinemia disorders: Malabsorption in Caco2 cell models and severe deficiency in patients

BACKGROUND

Familial hypobetalipoproteinemias (FHBL) are rare genetic diseases characterized by lipid malabsorption. We focused on abetalipoproteinemia (FHBL-SD1) and chylomicron retention disease (FHBL-SD3), caused by mutations in microsomal triglyceride transfer protein (MTTP) and SAR1B genes, respectively. Treatments include a low-fat diet and high-dose fat-soluble vitamin supplementations. However, patients are not supplemented in carotenoids, a group of lipid-soluble pigments essential for eye health.

OBJECTIVE

Our aim was to evaluate carotenoid absorption and status in the context of hypobetalipoproteinemia.

METHODS

We first used knock-out Caco-2/TC7 cell models of FHBL-SD1 and FHBL-SD3 to evaluate carotenoid absorption. We then characterized FHBL-SD1 and FHBL-SD3 patient status in the main dietary carotenoids and compared it to that of control subjects.

RESULTS

In vitro results showed a significant decrease in basolateral secretion of α- and β-carotene, lutein, and zeaxanthin (-88.8 ± 2.2 % to -95.3 ± 5.8 %, -79.2 ± 4.4 % to -96.1 ± 2.6 %, -91.0 ± 4.5 % to -96.7 ± 0.3 % and -65.4 ± 3.6 % to -96.6 ± 1.9 %, respectively). Carotenoids plasma levels in patients confirmed significant deficiencies, with decreases ranging from -89 % for zeaxanthin to -98 % for α-carotene, compared to control subjects.

CONCLUSION

Given the continuous loss in visual function despite fat-soluble vitamin treatment in some patients, carotenoid supplementation may be of clinical utility. Future studies should assess the correlation between carotenoid status and visual function in aging patients and investigate whether carotenoid supplementation could prevent their visual impairment.

Microsomal triglyceride transfer protein is necessary to maintain lipid homeostasis and retinal function

Lipid processing by the retinal pigment epithelium (RPE) is necessary to maintain retinal health and function. Dysregulation of retinal lipid homeostasis due to normal aging or to age-related disease triggers lipid accumulation within the RPE, on Bruch's membrane (BrM), and in the subretinal space. In its role as a hub for lipid trafficking into and out of the neural retina, the RPE packages a significant amount of lipid into lipid droplets for storage and into apolipoprotein B (apoB)-containing lipoproteins (Blps) for export. Microsomal triglyceride transfer protein (MTP), encoded by the MTTP gene, is essential for Blp assembly. Herein we test the hypothesis that MTP expression in the RPE is essential to maintain lipid balance and retinal function using the newly generated RPEΔMttp mouse model. Using non-invasive ocular imaging, electroretinography, and histochemical and biochemical analyses we show that genetic deletion of Mttp from the RPE results in intracellular lipid accumulation, increased photoreceptor -associated cholesterol deposits and photoreceptor cell death, and loss of rod but not cone function. RPE-specific ablation of Mttp had no significant effect on plasma lipids and lipoproteins. While, apoB was decreased in the RPE, ocular retinoid concentrations remained unchanged. Thus suggesting that RPE MTP is critical for Blp synthesis and assembly but not directly involved in ocular retinoid and plasma lipoprotein metabolism. These studies demonstrate that RPE-specific MTP expression is necessary to establish and maintain retinal lipid homeostasis and visual function.

Severe hypertriglyceridemia: Existing and emerging therapies

Severe hypertriglyceridemia (sHTG), defined as a triglyceride (TG) concentration ≥ 500 mg/dL (≥ 5.7 mmol/L) is an important risk factor for acute pancreatitis. Although lifestyle, some medications, and certain conditions such as diabetes may lead to HTG, sHTG results from a combination of major and minor genetic defects in proteins that regulate TG lipolysis. Familial chylomicronemia syndrome (FCS) is a rare disorder caused by complete loss of function in lipoprotein lipase (LPL) or LPL activating proteins due to two homozygous recessive traits or compound heterozygous traits. Multifactorial chylomicronemia syndrome (MCS) and sHTG are due to the accumulation of rare heterozygous variants and polygenic defects that predispose individuals to sHTG phenotypes. Until recently, treatment of sHTG focused on lifestyle interventions, control of secondary factors, and nonselective pharmacotherapies that had modest TG-lowering efficacy and no corresponding reductions in atherosclerotic cardiovascular disease events. Genetic discoveries have allowed for the development of novel pathway-specific therapeutics targeting LPL modulating proteins. New targets directed towards inhibition of apolipoprotein C-III (apoC-III), angiopoietin-like protein 3 (ANGPTL3), angiopoietin-like protein 4 (ANGPTL4), and fibroblast growth factor-21 (FGF21) offer far more efficacy in treating the various phenotypes of sHTG and opportunities to reduce the risk of acute pancreatitis and atherosclerotic cardiovascular disease events.

Missense mutation Q384K in the APOB gene affecting the large lipid transfer module of apoB reduces the secretion of apoB-100 in the liver without reducing the secretion of apoB-48 in the intestine

BACKGROUND

Molecular genetic testing of patients with hypobetalipoproteinemia may identify a genetic cause that can form the basis for starting proper therapy. Identifying a genetic cause may also provide novel data on the structure-function relationship of the mutant protein.

OBJECTIVE

To identify a genetic cause of hypobetalipoproteinemia in a patient with levels of low density lipoprotein cholesterol at the detection limit of 0.1 mmol/l.

METHODS

DNA sequencing of the translated exons with flanking intron sequences of the genes adenosine triphosphate-binding cassette transporter 1, angiopoietin-like protein 3, apolipoprotein B, apolipoprotein A1, lecithin-cholesterol acyltransferase, microsomal triglyceride transfer protein and proprotein convertase subtilisin/kexin type 9.

RESULTS

The patient was homozygous for mutation Q384K (c.1150C>A) in the apolipoprotein B gene, and this mutation segregated with hypobetalipoproteinemia in the family. Residue Gln384 is located in the large lipid transfer module of apoB that has been suggested to be important for lipidation of apolipoprotein B through interaction with microsomal triglyceride transfer protein. Based on measurements of serum levels of triglycerides and apolipoprotein B-48 after an oral fat load, we conclude that the patient was able to synthesize apolipoprotein B-48 in the intestine in a seemingly normal fashion.

CONCLUSION

Our data indicate that mutation Q384K severely reduces the secretion of apolipoprotein B-100 in the liver without reducing the secretion of apolipoprotein B-48 in the intestine. Possible mechanisms for the different effects of this and other missense mutations affecting the large lipid transfer module on the two forms of apoB are discussed.

Prevalence and prognosis of genetically proven familial hypercholesterolemia in subjects with coronary artery disease and reduced ejection fraction

Few studies have genetically screened variants related to familial hypercholesterolemia (FH) and investigated their survival impact in patients with coronary artery disease (CAD) and reduced left ventricular ejection fraction (EF). Patients with CAD and reduced EF (< 40%) were enrolled. Their genomic DNAs were sequenced for FH-related genes. All-cause and cardiovascular mortality data served as the major outcome. A total of 256 subjects were analyzed and 12 subjects (4.7%) carried FH-related genetic variants. After a median follow-up period of 44 months, 119 of the study subjects died. Cox survival analysis showed that carrying the FH genetic variant did not have a significant impact on the survival of CAD with reduced EF. However, higher estimated glomerular filtration rate (eGFR), better EF and beta blocker use were protective for a lower all-cause mortality. Further larger studies are needed to evaluate the impact of carrying the FH-related genetic variant on survival of CAD with reduced EF.

A case of hypocholesterolemia under study

Primary hypocholesterolemia (or hypobetalipoproteinemia) is a rare disorder of lipoprotein metabolism that may be due to a polygenic predisposition or a monogenic disease. Among these, it is possible to differentiate between symptomatic and asymptomatic forms, in which, in the absence of secondary causes, the initial clinical suspicion is plasma ApoB levels below the 5th percentile of the distribution by age and sex. Here we describe the differential diagnosis of a case of asymptomatic hypocholesterolemia. We studied proband's clinical data, the lipid profile of the proband and her relatives and the clinical data of the family relevant to carry out the differential diagnosis. We performed a genetic study as the diagnostic test. The information obtained from the differential diagnosis suggested a heterozygous hypobetalipoproteinemia due to PCSK9 loss-of-function variants. The diagnostic test revealed, in the proband, the presence of a heterozygous PCSK9 frame-shift variant of a maternal origin. Plasma levels of LDL cholesterol and PCSK9 of the patient and her relatives were compatible with the segregation of the variant revealed. In conclusion, the diagnostic test performed confirmed the suspected diagnosis of the proband as asymptomatic familial hypobetalipoproteinemia due to a loss-of-function variant in the PCSK9 gene.

Non-alcoholic fatty liver disease in a pediatric patient with heterozygous familial hypobetalipoproteinemia due to a novel APOB variant: a case report and systematic literature review

Background

Familial hypobetalipoproteinemia (FHBL) is an autosomal semi-dominant disorder usually caused by variants in the APOB gene that frequently interferes with protein length. Clinical manifestations include malabsorption, non-alcoholic fatty liver disease, low levels of lipid-soluble vitamins, and neurological, endocrine, and hematological dysfunction.

Methods

Genomic DNA was isolated from the blood samples of the pediatric patient with hypocholesterolemia and his parents and brother. Next-generation sequencing (NGS) was performed, and an expanded dyslipidemia panel was employed for genetic analysis. In addition, a systematic review of the literature on FHBL heterozygous patients was performed.

Case report

Genetic investigation revealed the presence of a heterozygous variant in the APOB (NM_000384.3) gene c.6624dup[=], which changes the open reading frame and leads to early termination of translation into the p.Leu2209IlefsTer5 protein (NP_000375.3). The identified variant was not previously reported. Familial segregation analysis confirmed the variant in the mother of the subject, who also has a low level of low-density lipoprotein and non-alcoholic fatty liver disease. We have introduced therapy that includes limiting fats in the diet and adding lipid-soluble vitamins E, A, K, and D and calcium carbonate. We reported 35 individuals with APOB gene variations linked to FHBL in the systematic review.

Conclusion

We have identified a novel pathogenic variant in the APOB gene causing FHBL in pediatric patients with hypocholesterolemia and fatty liver disease. This case illustrates the importance of genetic testing for dyslipidemias in patients with significant decreases in plasma cholesterol as we can avoid damaging neurological and ophthalmological effects by sufficient vitamin supplementation and regular follow-ups.

Low cholesterol states: clinical implications and management

INTRODUCTION

Hypocholesterolemia results from genetic - both monogenic and polygenic - and non-genetic causes and can sometimes be a source of clinical concern. We review etiologies and sequelae of hypocholesterolemia and therapeutics inspired from genetic hypocholesterolemia.

AREAS COVERED

Monogenic hypocholesterolemia disorders caused by the complete absence of apolipoprotein (apo) B-containing lipoproteins (abetalipoproteinemia and homozygous hypobetalipoproteinemia) or an isolated absence of apo B-48 lipoproteinemia (chylomicron retention disease) lead to clinical sequelae. These include gastrointestinal disturbances and severe vitamin deficiencies that affect multiple body systems, i.e. neurological, musculoskeletal, ophthalmological, and hematological. Monogenic hypocholesterolemia disorders with reduced but not absent levels of apo B lipoproteins have a milder clinical presentation and patients are protected against atherosclerotic cardiovascular disease. Patients with heterozygous hypobetalipoproteinemia have somewhat increased risk of hepatic disease, while patients with PCSK9 deficiency, ANGPTL3 deficiency, and polygenic hypocholesterolemia typically have anunremarkable clinical presentation.

EXPERT OPINION

In patients with severe monogenic hypocholesterolemia, early initiation of high-dose vitamin therapy and a low-fat diet are essential for optimal prognosis. The molecular basis of monogenic hypocholesterolemia has inspired novel therapeutics to help patients with the opposite phenotype - i.e. elevated apo B-containing lipoproteins. In particular, inhibitors of PCSK9 and ANGPTL3 show important clinical impact.

Fat-soluble vitamin and phytochemical metabolites: Production, gastrointestinal absorption, and health effects

Consumption of diets rich in fruits and vegetables, which provide some fat-soluble vitamins and many phytochemicals, is associated with a lower risk of developing certain degenerative diseases. It is well accepted that not only the parent compounds, but also their derivatives formed upon enzymatic or nonenzymatic transformations, can produce protective biological effects. These derivatives can be formed during food storage, processing, or cooking. They can also be formed in the lumen of the upper digestive tract during digestion, or via metabolism by microbiota in the colon. This review compiles the known metabolites of fat-soluble vitamins and fat-soluble phytochemicals (FSV and FSP) that have been identified in food and in the human digestive tract, or could potentially be present based on the known reactivity of the parent compounds in normal or pathological conditions, or following surgical interventions of the digestive tract or consumption of xenobiotics known to impair lipid absorption. It also covers the very limited data available on the bioavailability (absorption, intestinal mucosa metabolism) and summarizes their effects on health. Notably, despite great interest in identifying bioactive derivatives of FSV and FSP, studying their absorption, and probing their putative health effects, much research remains to be conducted to understand and capitalize on the potential of these molecules to preserve health.