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.

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.

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.

Familial ApoB-specific familial hypobetalipoproteinemia in a patient with non-classical congenital adrenal hyperplasia. / Hipobetalipoproteinemia familiar ApoB específica en una paciente con hiperplasia suprarrenal congénita no clásica.

Familial hypobetalipoproteinaemia is a disorder of lipid metabolism characterized by low levels of total cholesterol, low-density lipoprotein cholesterol and apolipoprotein B. ApoB-related familial hypolipoproteinemia is an autosomal condition with a codominance inheritance pattern. Non-classical congenital adrenal hyperplasia is an autosomal recessive disorder due to mutations in the CYP21A2, a gene encoding for the enzyme 21-hydroxylase, which results in an androgen excess production from adrenal source. We here present the case of a 25-year-old woman with NCAH showing decreased levels of total-cholesterol, low-density lipoprotein cholesterol and triglycerides. Her parent had digestive symptoms and severe hepatic steatosis with elevated liver enzymes, as well as decreased levels of total and low-density lipoprotein cholesterol. A genetic-molecular study of the proband identified a mutation in the APOB gene, which allowed a diagnosis of heterozygous ApoB-related hypolipoproteinaemia to be made.

Unique Genetic Features of Lean NAFLD: A Review of Mechanisms and Clinical Implications.

Non-alcoholic fatty liver disease (NAFLD) affects 25% of the global population. About 20% have a normal body mass index (BMI) and a variant known as lean NAFLD. Unlike typical NAFLD cases associated with obesity and diabetes, lean NAFLD causes liver disease by mechanisms not related to excess weight or insulin resistance. Genetic disorders are among the major factors in developing lean NAFLD, and genome-wide association studies have identified several genes associated with the condition. This review aims to increase awareness by describing the genetic markers linked to NAFLD and the defects involved in developing lean NAFLD.

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 ß-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.

Deep brain stimulation in Bassen-Kornzweig syndrome: Still effective after 22 years.

Introduction: Bassen-Kornzweig syndrome or abetalipoproteinemia is a rare autosomal recessive disorder characterized by a malabsorption of dietary fat and fat-soluble vitamins. This deficiency can lead to a variety of symptoms, including hematological (acanthocytosis, bleeding tendency), neurological (tremor, spinocerebellar ataxia), neuromuscular (myopathy), ophthalmological symptoms (retinitis pigmentosa). The thalamic ventral intermediate nucleus (VIM) is a well-established target for deep brain stimulation (DBS) in the treatment of refractory tremor. Research question: We evaluated the clinical long-term follow-up (22 years) after VIM-DBS for refractory tremor in abetalipoproteinemia. We also evaluated the adjustments of stimulation settings and medication balance after DBS procedure. Material and methods: We report a 53-year-old male who suffers from abetalipoproteinemia since the age of 17. He underwent bilateral VIM-DBS to treat his disabling refractory intentional tremor at the age of 31. He still has a very good response to his tremor with limited stimulation adaptations over 22 years. For more than two decades follow-up, the treatment significantly improved his ADL functions and therefore also the QoL. Discussion and conclusion: The VIM target for DBS in the treatment of refractory tremor has been extensively reported in the literature. Thalamic VIM-DBS is a safe and effective treatment for a severe, refractory tremor as a neurological symptom caused by abetalipoproteinemia. It also highlights the importance of a multidisciplinary follow-up, to adjust and optimize the stimulation/medication balance after VIM-DBS surgery.

Inborn Errors of Metabolism with Ataxia: Current and Future Treatment Options.

A number of hereditary ataxias are caused by inborn errors of metabolism (IEM), most of which are highly heterogeneous in their clinical presentation. Prompt diagnosis is important because disease-specific therapies may be available. In this review, we offer a comprehensive overview of metabolic ataxias summarized by disease, highlighting novel clinical trials and emerging therapies with a particular emphasis on first-in-human gene therapies. We present disease-specific treatments if they exist and review the current evidence for symptomatic treatments of these highly heterogeneous diseases (where cerebellar ataxia is part of their phenotype) that aim to improve the disease burden and enhance quality of life. In general, a multimodal and holistic approach to the treatment of cerebellar ataxia, irrespective of etiology, is necessary to offer the best medical care. Physical therapy and speech and occupational therapy are obligatory. Genetic counseling is essential for making informed decisions about family planning.

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.

Validation of Knock-Out Caco-2 TC7 Cells as Models of Enterocytes of Patients with Familial Genetic Hypobetalipoproteinemias.

Abetalipoproteinemia (FHBL-SD1) and chylomicron retention disease (FHBL-SD3) are rare recessive disorders of lipoprotein metabolism due to mutations in MTTP and SAR1B genes, respectively, which lead to defective chylomicron formation and secretion. This results in lipid and fat-soluble vitamin malabsorption, which induces severe neuro-ophthalmic complications. Currently, treatment combines a low-fat diet with high-dose vitamin A and E supplementation but still fails in normalizing serum vitamin E levels and providing complete ophthalmic protection. To explore these persistent complications, we developed two knock-out cell models of FHBL-SD1 and FHBL-SD3 using the CRISPR/Cas9 technique in Caco-2/TC7 cells. DNA sequencing, RNA quantification and Western blotting confirmed the introduction of mutations with protein knock-out in four clones associated with i) impaired lipid droplet formation and ii) defective triglyceride (-57.0 ± 2.6% to -83.9 ± 1.6%) and cholesterol (-35.3 ± 4.4% to -60.6 ± 3.5%) secretion. A significant decrease in α-tocopherol secretion was also observed in these clones (-41.5 ± 3.7% to -97.2 ± 2.8%), even with the pharmaceutical forms of vitamin E: tocopherol-acetate and tocofersolan (α-tocopheryl polyethylene glycol succinate 1000). MTTP silencing led to a more severe phenotype than SAR1B silencing, which is consistent with clinical observations. Our cellular models thus provide an efficient tool to experiment with therapeutic strategies and will allow progress in understanding the mechanisms involved in lipid metabolism.

Marked Acanthocytosis Associated With Klipple Trenaunay Syndrom.

Klipple-Trenaunay syndrome (KTS) is an extremely rare congenital vascular disorder with poorly defined incidence and prevalence. We report a case of a patient who presented after road traffic accident with primary complaints of poor wound healing and persistent bleeding from wound site. Discernible presence of arteriovenous malformation and skin hypertrophy since birth lead to the diagnosis of Klipple-Trenaunay syndrome (KTS). There was an incidental finding of acanthocytosis on peripheral film of blood which remained elevated even after clinical improvement of the patient. This case report highlights a close association of marked acanthocytosis of red blood cells and Klipple-Trenaunay syndrome.

[Homozygous familial hypobetalipoproteinemia caused by APOB gene variations: a case report and review of literature].

Objective: To summarize the genotypes and clinical characteristics of homozygous family hypobetalipoproteinemia (Ho-FHBL) caused by apolipoprotein B (APOB) gene variations. Methods: The clinical, laboratory, genetic, and liver histology data of a boy with Ho-FHBL managed in the hepatology ward of the Children's Hospital of Fudan University in May 2021 were retrospectively analyzed. The literature was searched from China National Knowledge Infrastructure, Wanfang Data Knowledge Service Platform, China VIP database, China Biology Medicine disc and PubMed database (up to May 2022) with "familial hypobetalipoproteinemia" or "hypobetalipoproteinemias" or "hypo beta lipoproteinemia" or "hypolipoproteinemias" as the search terms. All relevant literatures were reviewed to summarize the clinical and genetic features of Ho-FHBL caused by APOB gene variations. Results: The male patient was admitted to the hospital due to abnormal liver function tests for 8 months at the age of 4 years and 6 months. Blood biochemistry showed transaminitis and abnormally low serum levels of lipids. Liver biopsy revealed fatty liver with inflammation and early cirrhosis (Brunt score was F3G2S4). Whole exome sequencing revealed two novel variants of APOB gene (c.3745C>T, p.Q1249 * from the father and c.4589_4592delinsAGGTAGGAGGTTTAACTCCTCCTACCT, p.T1530Kfs * 12 from the mother). He was diagnosed as Ho-FHBL caused by APOB gene compound heterozygous variations. Literature search retrieved 36 English literatures and 0 Chinese literature. A total of 55 (23 males and 32 females) Ho-FHBL cases, including this one, were caused by 54 APOB gene pathogenic variants (23 frameshift, 15 nonsense, 7 missense, 8 splice and 1 gross deletions). The age of the last follow-up was between 1 month and 75 years. Among them, 28 cases had lipid malabsorption, 19 cases had early dysplasia, 12 cases had no symptoms. Twenty-one patients had symptoms related to fat soluble vitamin deficiency, including 14 cases of acanthocytosis, 10 cases of neurological symptoms, and 6 cases of ocular lesions. Thirty-four patients had liver involvement, including 25 cases of elevated transaminase, 21 cases of fatty liver, 15 cases of hepatomegaly, 9 cases of liver fibrosis, 3 cases of liver cirrhosis, 1 case of hepatic hemangioma and 1 case of liver neoplastic nodule. Conclusions: The variants of APOB gene in Ho-FHBL are mainly frameshift and nonsense variations. Patients may have lipid malabsorption and (or) early dysplasia, or symptom-free. Liver involvement is common.

Abetalipoproteinemia

An autosomal recessive disorder of lipid metabolism. It is caused by mutation of the microsomal triglyceride transfer protein that catalyzes the transport of lipids (TRIGLYCERIDES; CHOLESTEROL ESTERS; PHOSPHOLIPIDS) and is required in the secretion of BETA-LIPOPROTEINS (low density lipoproteins or LDL). Features include defective intestinal lipid absorption, very low serum cholesterol level, and near absent LDL.

Trastorno del metabolismo lipídico que se hereda como rasgo autosómico recesivo y que se caracteriza por la ausencia casi total en el plasma de APOLIPOPROTEÍNAS B y de lipoproteínas que contienen apoB. La proteína que transfiere los triglicéridos microsomales es deficiente o está ausente en los enterocitos. Los hallazgos clínicos y de laboratorio incluyen acantocitosis, hipocolesterolemia, neuropatía periférica, degeneración columnar posterior, ataxia, y esteatorrea. Las capacidades intelectuales también pueden estar afectadas.

Transtorno autossômico recessivo do metabolismo lipídico. É causada por mutação da proteína transportadora de triglicerídeos microssomais que catalisa o transporte de lipídeos (TRIGLICERÍDEOS, ÉSTERES DE COLESTEROL, FOSFOLIPÍDEOS) e é necessária para a secreção de BETA-LIPOPROTEÍNAS (lipoproteínas de densidade baixa ou LDL). Entre as características estão deficiência na absorção de lipídeos intestinal, níveis muito baixos de colesterol sérico e LDL praticamente ausente.

Apolipoproteínas B

Major structural proteins of triacylglycerol-rich LIPOPROTEINS. There are two forms, apolipoprotein B-100 and apolipoprotein B-48, both derived from a single gene. ApoB-100 expressed in the liver is found in low-density lipoproteins (LIPOPROTEINS, LDL; LIPOPROTEINS, VLDL). ApoB-48 expressed in the intestine is found in CHYLOMICRONS. They are important in the biosynthesis, transport, and metabolism of triacylglycerol-rich lipoproteins. Plasma Apo-B levels are high in atherosclerotic patients but non-detectable in ABETALIPOPROTEINEMIA.

Principales proteínas estructurales de LIPOPROTEÍNAS ricas en triacilglicerol. Hay dos formas, la apolipoproteína B-100 y la apolipoproteína B-48, ambas derivadas de un único gen. La ApoB-100 expresada en el hígado ocurre en lipoproteínas de baja densidad (LIPOPROTEÍNAS LDL; LIPOPROTEÍNAS VLDL). La ApoB-48 expresada en el intestino ocurre en QUILOMICRONES. Son importantes en la biosíntesis, el transporte, y en el metabolismo de lipoproteínas ricas en triacilglicerol. Los niveles plasmáticos de Apo-B son altos en pacientes ateroscleróticos pero no detectables en ABETALIPOPROTEINEMIA.

Principais proteínas estruturais das LIPOPROTEÍNAS ricas em triacilglicerol. Existem duas formas, a apolipoproteína B-100 e a apolipoproteína B-48, ambas provenientes de um único gene. A ApoB-100 expressa no fígado é encontrada nas lipoproteínas de baixa densidade (LIPOPROTEÍNAS LDL; LIPOPROTEÍNAS VLDL). A ApoB-48 expressa no intestino é encontrada em QUILOMÍCRONS. São importantes na biossíntese, no transporte, e no metabolismo de lipoproteínas ricas em triacilglicerol. Os níveis plasmáticos de Apo-B são altos em pacientes ateroscleróticos mão não detectáveis em ABETALIPOPROTEINEMIA.

Hipobetalipoproteinemia Familiar por Apolipoproteína B

An autosomal dominant disorder of lipid metabolism. It is caused by mutations of APOLIPOPROTEINS B, main components of CHYLOMICRONS and BETA-LIPOPROTEINS (low density lipoproteins or LDL). Features include abnormally low LDL, normal triglyceride level, and dietary fat malabsorption.

Trastorno autosómico dominante del metabolismo de los lípidos. Está causado por mutaciones de las APOLIPOPROTEÍNAS B, principales componentres de los QUILOMICRONES y BETA-LIPOPROTEÍNAS (lipoproteínas de baja densidad o LDL). Las características comprenden concentraciones anormalmente bajas de LDL, concentración normal de triglicéridos y malabsorción de las grasas de la dieta.

Transtorno autossômico dominante do metabolismo lipídico. É causada por mutações das APOLIPOPROTEÍNAS B, principais componentes dos QUILOMÍCRONS e beta-lipoproteínas (lipoproteínas de baixa densidade ou LDL). Entre as características estão LDL anormalmente baixa, níveis normal de triglicerídeos e malabsorção da gordura alimentar.

Homozygous familial hypobetalipoproteinemia caused by APOB gene variations: a case report and review of literature / 中华儿科杂志

Objective: To summarize the genotypes and clinical characteristics of homozygous family hypobetalipoproteinemia (Ho-FHBL) caused by apolipoprotein B (APOB) gene variations. Methods: The clinical, laboratory, genetic, and liver histology data of a boy with Ho-FHBL managed in the hepatology ward of the Children's Hospital of Fudan University in May 2021 were retrospectively analyzed. The literature was searched from China National Knowledge Infrastructure, Wanfang Data Knowledge Service Platform, China VIP database, China Biology Medicine disc and PubMed database (up to May 2022) with "familial hypobetalipoproteinemia" or "hypobetalipoproteinemias" or "hypo beta lipoproteinemia" or "hypolipoproteinemias" as the search terms. All relevant literatures were reviewed to summarize the clinical and genetic features of Ho-FHBL caused by APOB gene variations. Results: The male patient was admitted to the hospital due to abnormal liver function tests for 8 months at the age of 4 years and 6 months. Blood biochemistry showed transaminitis and abnormally low serum levels of lipids. Liver biopsy revealed fatty liver with inflammation and early cirrhosis (Brunt score was F3G2S4). Whole exome sequencing revealed two novel variants of APOB gene (c.3745C>T, p.Q1249 * from the father and c.4589_4592delinsAGGTAGGAGGTTTAACTCCTCCTACCT, p.T1530Kfs * 12 from the mother). He was diagnosed as Ho-FHBL caused by APOB gene compound heterozygous variations. Literature search retrieved 36 English literatures and 0 Chinese literature. A total of 55 (23 males and 32 females) Ho-FHBL cases, including this one, were caused by 54 APOB gene pathogenic variants (23 frameshift, 15 nonsense, 7 missense, 8 splice and 1 gross deletions). The age of the last follow-up was between 1 month and 75 years. Among them, 28 cases had lipid malabsorption, 19 cases had early dysplasia, 12 cases had no symptoms. Twenty-one patients had symptoms related to fat soluble vitamin deficiency, including 14 cases of acanthocytosis, 10 cases of neurological symptoms, and 6 cases of ocular lesions. Thirty-four patients had liver involvement, including 25 cases of elevated transaminase, 21 cases of fatty liver, 15 cases of hepatomegaly, 9 cases of liver fibrosis, 3 cases of liver cirrhosis, 1 case of hepatic hemangioma and 1 case of liver neoplastic nodule. Conclusions: The variants of APOB gene in Ho-FHBL are mainly frameshift and nonsense variations. Patients may have lipid malabsorption and (or) early dysplasia, or symptom-free. Liver involvement is common.

Guidance for the diagnosis and treatment of hypolipidemia disorders.

The Abetalipoproteinemia and Related Disorders Foundation was established in 2019 to provide guidance and support for the life-long management of inherited hypocholesterolemia disorders. Our mission is "to improve the lives of individuals and families affected by abetalipoproteinemia and related disorders". This review explains the molecular mechanisms behind the monogenic hypobetalipoproteinemia disorders and details their specific pathophysiology, clinical presentation and management throughout the lifespan. In this review, we focus on abetalipoproteinemia, homozygous hypobetalipoproteinemia and chylomicron retention disease; rare genetic conditions that manifest early in life and cause severe complications without appropriate treatment. Absent to low plasma lipid levels, in particular cholesterol and triglyceride, along with malabsorption of fat and fat-soluble vitamins are characteristic features of these diseases. We summarize the genetic basis of these disorders, provide guidance in their diagnosis and suggest treatment regimens including high dose fat-soluble vitamins as therapeutics. A section on preconception counseling and other special considerations pertaining to pregnancy is included. This information may be useful for patients, caregivers, physicians and insurance agencies involved in the management and support of affected individuals.