Chylomicron retention disease: genetics, biochemistry, and clinical spectrum.

PURPOSE OF REVIEW: Chylomicron retention disease (CRD) is an autosomic recessive disorder, in which intestinal fat malabsorption is the main cause of diverse severe manifestations. The specific molecular defect was identified in 2003 and consists of mutations in the SAR1B or SARA2 gene encoding for intracellular SAR1B GTPase protein. The aim of this review is first to provide an update of the recent biochemical, genetic and clinical findings, and second to discuss novel mechanisms related to hallmark symptoms. RECENT FINDINGS: CRD patients present with SAR1B mutations, which disable the formation of coat protein complex II and thus blocks the transport of chylomicron cargo from the endoplasmic reticulum to the Golgi. Consequently, there is a total absence of chylomicron and apolipoprotein B-48 in the blood circulation following a fat meal, accompanied by a deficiency in liposoluble vitamins and essential fatty acids. The recent discovery of Transport and Golgi organization and Transport and Golgi organization-like proteins may explain the intriguing export of large chylomicron, exceeding coat protein complex II size. Hypocholesterolemia could be accounted for by a decrease in HDL cholesterol, likely a reflection of limited production of intestinal HDL in view of reduced ATP-binding cassette family A protein 1 and apolipoprotein A-I protein. In experimental studies, the paralog SAR1A compensates for the lack of the SAR1B GTPase protein. SUMMARY: Molecular testing for CRD is recommended to distinguish the disease from other congenital fat malabsorptions, and to early define molecular aberrations, accelerate treatment, and prevent complications.

Effects of angiopoietin-like protein 3 deficiency on postprandial lipid and lipoprotein metabolism.

The consequences of angiopoietin-like protein 3 (ANGPTL3) deficiency on postprandial lipid and lipoprotein metabolism has not been investigated in humans. We studied 7 homozygous (undetectable circulating ANGPTL3 levels) and 31 heterozygous (50% of circulating ANGPTL3 levels) subjects with familial combined hypolipidemia (FHBL2) due to inactivating ANGPTL3 mutations in comparison with 35 controls. All subjects were evaluated at fasting and during 6 h after a high fat meal. Postprandial lipid and lipoprotein changes were quantified by calculating the areas under the curve (AUCs) using the 6 h concentration data. Plasma changes of ß-hydroxybutyric acid (ß-HBA) were measured as marker of hepatic oxidation of fatty acids. Compared with controls, homozygotes showed lower incremental AUCs (iAUCs) of total TG (-69%, P < 0.001), TG-rich lipoproteins (-90%, P < 0.001), apoB-48 (-78%, P = 0.032), and larger absolute increase of FFA (128%, P < 00.1). Also, heterozygotes displayed attenuated postprandial lipemia, but the difference was significant only for the iAUC of apoB-48 (-28%; P < 0.05). During the postprandial period, homozygotes, but not heterozygotes, showed a lower increase of ß-HBA. Our findings demonstrate that complete ANGPTL3 deficiency associates with highly reduced postprandial lipemia probably due to faster catabolism of intestinally derived lipoproteins, larger expansion of the postprandial FFA pool, and decreased influx of dietary-derived fatty acids into the liver. These results add information on mechanisms underlying hypolipidemia in FHBL2.

The endoplasmic reticulum coat protein II transport machinery coordinates cellular lipid secretion and cholesterol biosynthesis.

Triglycerides and cholesterol are essential for life in most organisms. Triglycerides serve as the principal energy storage depot and, where vascular systems exist, as a means of energy transport. Cholesterol is essential for the functional integrity of all cellular membrane systems. The endoplasmic reticulum is the site of secretory lipoprotein production and de novo cholesterol synthesis, yet little is known about how these activities are coordinated with each other or with the activity of the COPII machinery, which transports endoplasmic reticulum cargo to the Golgi. The Sar1B component of this machinery is mutated in chylomicron retention disorder, indicating that this Sar1 isoform secures delivery of dietary lipids into the circulation. However, it is not known why some patients with chylomicron retention disorder develop hepatic steatosis, despite impaired intestinal fat malabsorption, and why very severe hypocholesterolemia develops in this condition. Here, we show that Sar1B also promotes hepatic apolipoprotein (apo) B lipoprotein secretion and that this promoting activity is coordinated with the processes regulating apoB expression and the transfer of triglycerides/cholesterol moieties onto this large lipid transport protein. We also show that although Sar1A antagonizes the lipoprotein secretion-promoting activity of Sar1B, both isoforms modulate the expression of genes encoding cholesterol biosynthetic enzymes and the synthesis of cholesterol de novo. These results not only establish that Sar1B promotes the secretion of hepatic lipids but also adds regulation of cholesterol synthesis to Sar1B's repertoire of transport functions.

Diagnostico de hipobetalipoproteinemia en un nino de 8 años? / Diagnosis of hypobetalipoproteinemia in an 8-year-old child? / Diagnostico hipobetalipoproteinemia numa crianca de 8 anos?

La hipobetalipoproteinemia familiar es un trastorno hereditario autosomico dominante que afecta a las lipoproteinas que contienen Apo B, una proteina indispensable para el transporte de los quilomicrones en el intestino y que ademas participa en la sintesis y transporte de las VLDL en el higado. La concentracion de Apo B se usa junto con otras pruebas lipidicas para establecer el riesgo individual de un paciente de desarrollar enfermedad cardiovascular. Presentacion del caso: Paciente de 8 anos, varon, que acude a la consulta de Pediatria del Hospital Universitario Virgen Macarena de Sevilla con sintomas de dolor abdominal, deposiciones blandas y diarreicas, sobrepeso y unas quebradizas. El paciente fue derivado al laboratorio para su estudio con sospecha de hipobetalipoproteinemia. Se le solicito un hemograma, frotis sanguineo, pruebas de coagulacion, bioquimica general y estudio de riesgo vascular. Los datos del estudio bioquimico descartaron la celiaquia (IgA 174 mg/dL [100- 400 mg/dL] y antitransglutaminasa 5 U/mL [< 20]). Las determinaciones incluidas en el perfil de riesgo cardiovascular (RCV) fueron: colesterol total 83 mg/dL (45 mg/dL), c-LDL 32 mg/dL (< 160 mg/dL), colesterol no HDL 35 mg/dL, c-VLDL 3 mg/dL (< 40 mg/dL), trigliceridos 28 mg/dL, Apo-A1 112 mg/dL (119-240 mg/dL), Apo B-100 25 mg/dL (40-125 mg/dL), us-PCR 1,47 mg/dL (< 3 mg/dL), Lp (a) 2 mg/dL (< 30 mg/ dL), homocisteina 5,8 µmol/L (< 15 µmol/L), vitamina A 42 µg/dL (50-200 µg/ dL), vitamina E 1051 µg/dL (50-180 µg/dL) y 25-(OH) D 48,9 ng/mL (30-54 ng/mL) en intervalos de normalidad. El HLA-27 fue negativo. Tras encontrar hallazgos bioquimicos de bajas concentraciones de lipoproteinas con Apo B, se le solicito al paciente una prueba de saliva para realizacion de estudio genetico de LipochipR para mutaciones en el gen de Apo B y PCSK9. Se concluye que el paciente presento una disminucion de la concentracion de las lipoproteinas que contienen Apo B y trigliceridos. La sintomatologia de dolor abdominal y heces pastosas apoyaron el diagnostico clinico. La inexistencia de deficit vitaminico, retraso mental, acantocitosis y demas sintomatologia asociada, hizo pensar en una herencia heterocigota, que con las herramientas disponibles no se pudo describir geneticamente ya que LipochipR no detecta positividad para este paciente para una mutacion de cambio de aminoacidos en el gen y exon de Apo 26, PCSK9-7, PCSK9-4, PCSK9-10.

Familial hypobetalipoproteinemia is a dominant autosomal inherited disorder that affects lipoproteins containing Apo B. It is an essential protein for the transport of chylomicrons in the intestine and it is involved in the synthesis and transport of VLDL in the liver. This concentration is used along with other lipid tests to establish a patient's individual risk of developing cardiovascular disease. This is the case of an 8 year-old male patient who presented at the University Hospital Virgen Macarena in Seville with symptoms of abdominal pain, loose stools and diarrhea, overweight and broken nails. The patient was referred to the laboratory for examination with suspected hypobetalipoproteinemia. He was requested a complete blood count, blood smear, coagulation, biochemistry and vascular risk study. Biochemical data discarded celiac disease (IgA 174 mg/dL [100-400 mg/dL] y antitransglutaminase antibody 5 U/mL [< 20]). Determinations were RCV's profile: Total cholesterol 83 mg/dL (45 mg/dL), c-LDL 32 mg/dL (< 160 mg/dL), non-HDL cholesterol 35 mg/dL, c-VLDL 3 mg/dL (< 40 mg/dL), triglycerides 28 mg/dL, Apo-A1 112 mg/dL (119-240 mg/dL), Apo B-100 25 mg/dL (40-125 mg/dL), us-PCR 1,47 mg/dL (< 3 mg/dL), Lp (a) 2 mg/dL (< 30 mg/dL), Homocysteine 5,8 µmol/L (< 15 µmol/L), Vitamin A 42 µg/dL (50-200 µg/dL), Vitamine E 1051 µg/dL (50-180 µg/dL) and 25-(OH) D 48,9 ng/mL (30-54 ng/mL) in normal ranges. HLA-27 Negative. After biochemical findings of low concentrations of lipoproteins with Apo B100, the patient was requested a saliva test for genetic study conducting LipochipR for mutations of Apo B and PCSK9. It can be concluded that the patient had a decreased concentration of lipoproteins containing Apo-B and triglycerides. The symptoms of abdominal pain and tarry stools supported the clinical diagnosis. The lack of vitamin deficiency, mental retardation, acanthocytosis and other associated sintomatology, made it possible to consider it an heterozygous inheritance. which could not be genetically described with the tools available since LipochipR does not detect in this patient positivity for a mutation to the amino acid change in the gene and exon 26 of Apo, Apo 26, PCSK9-7, PCSK9- 4, PCSK9-10.

Hypobetalipoproteinemia familiar e um disturbio autossomico hereditario dominante que afeta as lipoproteinas contendo Apo--B, uma proteina essencial para o transporte de quilomicrons no intestino e esta envolvido na sintese e transporte de VLDL no figado. A concentracao de Apo-B e utilizada, juntamente com outros testes lipidicos, para estabelecer o risco individual de um paciente de desenvolver doencas cardiovasculares. O caso e o de um paciente de 8 anos, do sexo masculino, que se apresenta para consulta de Pediatria do Hospital Universitario Virgen Macarena, em Sevilha, com sintomas de dor abdominal, fezes brandas e diarreia, sobrepeso e unhas quebradicas. O paciente foi derivado ao laboratorio para exame com suspeita de hypobetalipoproteinemia. Foi pedido um hemograma completo, esfregaco de sangue, coagulacao, bioquimica geral e estudo de risco vascular. Os dados do estudo bioquimico descartaram a doenca celiaca (IgA 174 mg/dL [100-400 mg/dL] e Antitrasglutaminase 5 U/mL [<20]). As determinacoes incluidas no perfil de risco cardiovascular (RCV) foram colesterol total 83 mg/dL (45 mg/dL), LDL-C 32 mg/ dL (<160 mg/dL), colesterol nao-HDL de 35 mg/dL, VLDL-C 3 mg/dL (<40 mg/dL), triglicerideos de 28 mg/dL, Apo-A1 112 mg/ dL (119-240 mg/dL), Apo B-100-25 mg/dL (40-125 mg/dL), us-PCR 1,47 mg/dL (<3 mg/dL) de Lp (a) 2 mg/dL (<30 mg/dL), homocisteina de 5,8 µmol/L (<15 µmol/L), a vitamina A 42 µg/dL (50-200 µg/dL), vitamina E 1051 µg/dL (50-180 µg/dL) e 25- (OH) D 48,9 ng/mL (30-54 ng/mL) em intervalos de normalidade. O HLA-27 foi negativo. Depois de encontrar achados bioquimicos de baixas concentracoes de lipoproteinas com apo-B, foi solicitado ao paciente um teste de saliva para estudo genetico de LipochipR para mutacoes no gene de Apo-B e PCSK9. Conclui-se que o paciente apresentou uma diminuicao na concentracao das lipoproteinas contendo Apo-B e triglicerideos. Os sintomas de dor abdominal e fezes pastosas apoiaram o diagnostico clinico. A inexistencia de deficit vitaminico, retardo mental, acantocitose e outros sintomas associados fez pensar numa heranca heterozigotica, que com as ferramentas disponiveis nao se pode descrever geneticamente ja que LipochipR nao detecta positividade para este paciente para uma mutacao de mudanca de aminoacidos no gene e exon de Apo 26, PCSK9-7, PCSK9- 4, PCSK9-10.

LDL but not HDL increases adiponectin release of primary human adipocytes.

Adipocytes in obesity have inappropriately low cholesterol while adiponectin release is reduced. Cholesterol shortage may contribute to low adiponectin and 3T3-L1 cells treated with lovastatin have diminished adiponectin in cell supernatants. LDL and HDL deliver cholesterol to adipocytes. LDL but not HDL increases adiponectin in cell supernatants of primary human adipocytes. The effect of LDL is not blocked by receptor associated protein suggesting that members of the LDL-receptor family are not involved. To evaluate whether these in vitro observations translate into changes in systemic adiponectin, adiponectin was measured in serum of three patients before, immediately after and 3d after LDL-apheresis. Whereas circulating lipoproteins are reduced immediately after apheresis adiponectin is not changed. Therefore, acute lowering of lipoproteins does not affect systemic adiponectin also excluding that plenty of adiponectin is bound to lipoprotein particles. Accordingly, levels of adiponectin in purified lipoproteins are quite low. Familial hypobetalipoproteinemia (FHBL) is a rare disorder associated with low plasma LDL. Serum adiponectin is, however, similar compared to healthy controls. Thus, neither LDL nor HDL directly contributes to circulating adiponectin concentrations.

Characterization of three kindreds with familial combined hypolipidemia caused by loss-of-function mutations of ANGPTL3.

BACKGROUND: Angiopoietin-like protein 3 (ANGPTL3) affects lipid metabolism by inhibiting the activity of lipoprotein and endothelial lipases. Angptl3 knockout mice have marked hypolipidemia, and heterozygous carriers of ANGPLT3, loss-of-function mutations were found among individuals in the lowest quartile of plasma triglycerides in population studies. Recently, 4 related individuals with primary hypolipidemia were found to be compound heterozygotes for ANGPTL3 loss-of-function mutations. METHODS AND RESULTS: We resequenced ANGPTL3 in 4 members of 3 kindreds originally identified for very low levels of low-density lipoprotein cholesterol and high-density lipoprotein cholesterol (0.97±0.16 and 0.56±0.20 mmol/L, respectively) in whom no mutations of known candidate genes for monogenic hypobetalipoproteinemia and hypoalphalipoproteinemia had been detected. These subjects were found to be homozygous or compound heterozygous for ANGPTL3 loss-of-function mutations (p.G400VfsX5, p.I19LfsX22/p.N147X) associated with the absence of ANGPTL3 in plasma. They had reduced plasma levels of triglyceride-containing lipoproteins and of HDL particles that contained only apolipoprotein A-I and pre-ß-high-density lipoprotein. In addition, their apolipoprotein B-depleted sera had a reduced capacity to promote cell cholesterol efflux through the various pathways (ABCA1-, SR-BI-, and ABCG1-mediated efflux); however, these subjects had no clinical evidence of accelerated atherosclerosis. Heterozygous carriers of the ANGPTL3 mutations had low plasma ANGPTL3 and moderately reduced low-density lipoprotein cholesterol (2.52±0.38 mmol/L) but normal plasma high-density lipoprotein cholesterol. CONCLUSIONS: Complete ANGPTL3 deficiency caused by loss-of-function mutations of ANGPTL3 is associated with a recessive hypolipidemia characterized by a reduction of apolipoprotein B and apolipoprotein A-I-containing lipoproteins, changes in subclasses of high-density lipoprotein, and reduced cholesterol efflux potential of serum. Partial ANGPTL3 deficiency is associated only with a moderate reduction of low-density lipoprotein.

Anderson's disease/chylomicron retention disease in a Japanese patient with uniparental disomy 7 and a normal SAR1B gene protein coding sequence.

BACKGROUND: Anderson's Disease (AD)/Chylomicron Retention Disease (CMRD) is a rare hereditary hypocholesterolemic disorder characterized by a malabsorption syndrome with steatorrhea, failure to thrive and the absence of chylomicrons and apolipoprotein B48 post-prandially. All patients studied to date exhibit a mutation in the SAR1B gene, which codes for an essential component of the vesicular coat protein complex II (COPII) necessary for endoplasmic reticulum to Golgi transport. We describe here a patient with AD/CMRD, a normal SAR1B gene protein coding sequence and maternal uniparental disomy of chromosome 7 (matUPD7). METHODS AND RESULTS: The patient, one of two siblings of a Japanese family, had diarrhea and steatorrhea beginning at five months of age. There was a white duodenal mucosa upon endoscopy. Light and electron microscopy showed that the intestinal villi were normal but that they had lipid laden enterocytes containing accumulations of lipid droplets in the cytoplasm and lipoprotein-size particles in membrane bound structures. Although there were decreased amounts in plasma of total- and low-density lipoprotein cholesterol, apolipoproteins AI and B and vitamin E levels, the triglycerides were normal, typical of AD/CMRD. The presence of low density lipoproteins and apolipoprotein B in the plasma, although in decreased amounts, ruled out abetalipoproteinemia. The parents were asymptomatic with normal plasma cholesterol levels suggesting a recessive disorder and ruling out familial hypobetalipoproteinemia. Sequencing of genomic DNA showed that the 8 exons of the SAR1B gene were normal. Whole genome SNP analysis and karyotyping revealed matUPD7 with a normal karyotype. In contrast to other cases of AD/CMRD which have shown catch-up growth following vitamin supplementation and a fat restricted diet, our patient exhibits continued growth delay and other aspects of the matUPD7 and Silver-Russell Syndrome phenotypes. CONCLUSIONS: This patient with AD/CMRD has a normal SAR1B gene protein coding sequence which suggests that factors other than the SAR1B protein may be crucial for chylomicron secretion. Further, this patient exhibits matUPD7 with regions of homozygosity which might be useful for elucidating the molecular basis of the defect(s) in this individual. The results provide novel insights into the relation between phenotype and genotype in these diseases and for the mechanisms of secretion in the intestine.

Neuroacanthocytosis syndromes.

Neuroacanthocytosis (NA) syndromes are a group of genetically defined diseases characterized by the association of red blood cell acanthocytosis and progressive degeneration of the basal ganglia. NA syndromes are exceptionally rare with an estimated prevalence of less than 1 to 5 per 1'000'000 inhabitants for each disorder. The core NA syndromes include autosomal recessive chorea-acanthocytosis and X-linked McLeod syndrome which have a Huntington's disease-like phenotype consisting of a choreatic movement disorder, psychiatric manifestations and cognitive decline, and additional multi-system features including myopathy and axonal neuropathy. In addition, cardiomyopathy may occur in McLeod syndrome. Acanthocytes are also found in a proportion of patients with autosomal dominant Huntington's disease-like 2, autosomal recessive pantothenate kinase-associated neurodegeneration and several inherited disorders of lipoprotein metabolism, namely abetalipoproteinemia (Bassen-Kornzweig syndrome) and hypobetalipoproteinemia leading to vitamin E malabsorption. The latter disorders are characterized by a peripheral neuropathy and sensory ataxia due to dorsal column degeneration, but movement disorders and cognitive impairment are not present. NA syndromes are caused by disease-specific genetic mutations. The mechanism by which these mutations cause neurodegeneration is not known. The association of the acanthocytic membrane abnormality with selective degeneration of the basal ganglia, however, suggests a common pathogenetic pathway. Laboratory tests include blood smears to detect acanthocytosis and determination of serum creatine kinase. Cerebral magnetic resonance imaging may demonstrate striatal atrophy. Kell and Kx blood group antigens are reduced or absent in McLeod syndrome. Western blot for chorein demonstrates absence of this protein in red blood cells of chorea-acanthocytosis patients. Specific genetic testing is possible in all NA syndromes. Differential diagnoses include Huntington disease and other causes of progressive hyperkinetic movement disorders. There are no curative therapies for NA syndromes. Regular cardiologic studies and avoidance of transfusion complications are mandatory in McLeod syndrome. The hyperkinetic movement disorder may be treated as in Huntington disease. Other symptoms including psychiatric manifestations should be managed in a symptom-oriented manner. NA syndromes have a relentlessly progressive course usually over two to three decades.

Recurrent familial hypobetalipoproteinemia-induced nonalcoholic fatty liver disease after living donor liver transplantation.

Familial hypobetalipoproteinemia (FHBL) is one of the causes of nonalcoholic steatohepatitis (NASH) and a codominant disorder. Patients heterozygous for FHBL may be asymptomatic, although they demonstrate low plasma levels of low-density lipoprotein (LDL) cholesterol and apolipoprotein B. Here we report a nonobese 54-year-old man with decompensated liver cirrhosis who underwent living donor liver transplantation with his son as the donor. Low albuminemia and refractory ascites persisted after transplantation. A biopsy specimen obtained 11 months after liver transplantation revealed severe steatosis and fibrosis, and recurrent NASH was diagnosed on the basis of pathological findings. Both the patient's and donor's laboratory tests demonstrated low LDL cholesterol and apolipoprotein levels. Because mutations in messenger RNAs of microsomal triglyceride transfer protein and apolipoprotein B genes were excluded neither in the recipient nor in the donor, both were clinically diagnosed as being heterozygous for FHBL. We successfully treated the recipient with heterozygous FHBL-induced recurrent NASH after liver transplantation using our diet and exercise programs.

Apolipoprotein B gene mutations and fatty liver in Japanese hypobetalipoproteinemia.

BACKGROUND: Familial hypobetalipoproteinemia (FHBL) is a hereditary disorder characterized by decreased plasma concentrations of low-density lipoprotein cholesterol. The best-characterized causes of FHBL are apolipoprotein B (apoB) gene mutations, which produce truncated apoB proteins. Fatty liver is thought to be frequent in FHBL, owing to impaired secretion of very-low-density lipoprotein from the liver. Homozygotes for FHBL present with extremely low concentrations of plasma lipids, and may suffer from deficiencies of fat-soluble vitamins. The objectives of this study were to identify apoB-defective FHBL subjects and investigate fatty liver in Japanese population. METHODS: We screened 14 hypocholesterolemic subjects for apoB gene mutations by PCR-SSCP and performed liver ultrasonography in a Japanese population. RESULTS: We identified an apoB-82 homozygote in one subject and an apoB-13.7 heterozygote in another subject. Four of 6 individuals with FHBL presented with fatty liver in those 2 FHBL families. Liver biopsy of the apoB-13.7 heterozygote, which had obesity and insulin resistance, showed severe fatty liver. The apoB-82 homozygote was asymptomatic with fat-soluble vitamin concentrations being normal, possibly due to spared secretion of apoB-48 from the intestine and increased plasma concentrations of high-density lipoprotein cholesterol. CONCLUSION: ApoB gene mutations might not be rare and that fatty liver might be frequent in Japanese FHBL.

An MCA/MR syndrome with hypocholesterolemia due to familial hypobetalipoproteinemia: report of a second patient with Nguyen syndrome.

[Nguyen et al. (2003); Am J Med Genet 121A: 109-112] reported a boy with severe hypocholesterolemia due to autosomal dominant hypobetalipoproteinemia (ADBHL) associated with severe growth retardation, mental deficiency, epicanthal folds, a short nose with low nasal bridge and anteverted nares and bilateral partial cutaneous syndactyly of toes 2 and 3. Many of these manifestations resembled those in a mild form of Smith-Lemli-Opitz syndrome (SLOS). We report on a 13-year-old boy with ADHBL, who manifested a SLOS-like phenotype, including mental retardation and a characteristic face, similar to that of a patient reported by [Nguyen et al. (2003); Am J Med Genet 121A: 109-112]. Our patient supports the hypothesis by [Nguyen et al. (2003); Am J Med Genet 121A: 109-112] that ADHBL induced cholesterol deficiency has a significant effect on morphogenesis during embryogenesis, although additional genetic or environmental factors may be required to develop an SLOS-like phenotype in individuals with ADHLB. This is a second case of Nguyen syndrome.

[Hepatic steatosis associated with heterozygotic familial hypobetalipoproteinemia]. / Esteatosis hepática asociada a hipobetalipoproteinemia familiar heterocigótica. Presentación de un caso.

Fatty liver disease is now recognized as a major health burden, due to the greater number of cases that are being diagnosed. This trend could partly be explained by the increased use of liver ultrasonography in asymptomatic patients for various reasons, mainly persistent transaminase elevation. The most commonly reported risk factors associated with fatty liver disease are chronic alcohol intake, obesity, type 2 diabetes mellitus, hyperlipidemia, and some drugs. When these factors have been ruled out in a patient with a fatty liver, less frequent causes such as certain inherited metabolic disorders should be considered. Familial hypobetalipoproteinemia is characterized by an alteration of apolipoprotein B (apo B) synthesis, leading to the secretion of truncated forms of the protein, which in turn leads to a marked reduction in excretion of very low-density lipoproteins from the liver and consequently to lipid deposits, especially triglycerides, in the hepatocytes. We report the case of a 23-year-old man who met the diagnostic criteria for heterozygous familial hypobetalipoproteinemia. He presented with mild transaminase elevation and fatty liver. Total cholesterol, low-density lipoprotein cholesterol, very low-density lipoprotein cholesterol and apo B were below normal limits, while levels of high-density lipoprotein cholesterol were normal. Lipid profile determination and liver ultrasonography of first and second-degree relatives were also performed. Molecular studies of the index case revealed an unaffected apo B gene.

Chylomicron retention disease--the role of ultrastructural examination in differential diagnosis.

Three children with malabsorption presumably caused by celiac disease had undergone jejunal biopsy. While a histological examination revealed microvacuolization of enterocytes in the absence of celiac lesions, an ultrastructural investigation disclosed numerous chylomicrons and larger lipid vacuoles inside the cytoplasm of enterocytes, mostly in the supranuclear region. No chylomicrons were evident in the interstitium between adjacent enterocytes, as observed in normal subjects. These ultrastructural findings allowed for the diagnosis of "Chylomicron retention disease" (CRD). CRD was described for the first time by Anderson in 1961, and it is included in the group of disorders of biosynthesis and secretion of B apolipoproteins (apoB). This disease, in particular, appears to result from a specific defect involving the secretion of lipoproteins containing apoB-48 from the gut, with the complete absence of post prandial chylomicrons in the sera. CRD needs to be recognized early because of its adverse effects on growth and its potential for neurological and ocular complications, and the ultrastructural identification of chylomicron-size lipid droplets clustered in the enterocytes, with the absence of fat outside the cells, represents the gold standard to identify CRD. together with clinical aspects and laboratory measurements. In this study, we describe the histological and ultrastructural aspects observed in three pediatric cases of CRD.

Anderson's disease: exclusion of apolipoprotein and intracellular lipid transport genes.

Anderson's disease is a rare, hereditary hypocholesterolemic syndrome characterized by chronic diarrhea, steatorrhea, and failure to thrive associated with the absence of apo B48-containing lipoproteins. To further define the molecular basis of the disease, we studied 8 affected subjects in 7 unrelated families of North African origin after treatment with a low-fat diet. Lipid loading of intestinal biopsies persisted, but the pattern and extent of loading was variable among the patients. Electron microscopy showed lipoprotein-like particles in membrane-bound compartments, the densities (0.65 to 7.5 particles/mu(2)) and the mean diameters (169 to 580 nm) of which were, in general, significantly larger than in a normal fed subject (0.66 particles/mu(2), 209 nm mean diameter). There were also large lipid particles having diameters up to 7043 nm (average diameters from 368 to 2127 nm) that were not surrounded by a membrane. Rarely, lipoprotein-like particles 50 to 150 nm in diameter were observed in the intercellular spaces. Intestinal organ culture showed that apo B and apo AIV were synthesized with apparently normal molecular weights and that small amounts were secreted in lipid-bound forms (density <1.006 g/mL). Normal microsomal triglyceride transfer protein (MTP) and activity were also detected in intestinal biopsies. Segregation analyses of 4 families excluded, as a cause of the disease, significant regions of the genome surrounding the genes for apo AI, AIV, B, CI, CII, CIII, and E, as were the genes encoding 3 proteins involved in intracellular lipid transport, MTP, and fatty acid binding proteins 1 and 2. The results suggest that a factor other than apoproteins and MTP are important for human intestinal chylomicron assembly and secretion.

Diffuse fatty liver in familial heterozygous hypobetalipoproteinemia.

A 34-year-old man had asymptomatic hepatomegaly, slightly increased serum alanine aminotransferase and gamma-glutamyl transpeptidase levels, and a sonographic pattern suggesting diffuse hepatic steatosis. Liver biopsy revealed fatty change in 25% to 50% of hepatocytes. The patient also had low serum levels of cholesterol and triglycerides and met clinical, biochemical, and familial diagnostic criteria of heterozygous hypobetalipoproteinemia. We could not relate his hepatic steatosis to any already known cause of fatty liver and could only attribute it to heterozygous hypobetalipoproteinemia. Familial heterozygous hypobetalipoproteinemia should be ruled out in patients with unexplained hepatic steatosis.

[Snow white small intestinal villi in hypobetalipoproteinemia]. / Schneeweisse Dünndarmzotten bei Hypobetalipoproteinämie.

In contrast to the severe clinical picture of abetalipoproteinemia patients with hypobetalipoproteinemia are often asymptomatic. We demonstrate a 52-years-old female patient with a white mucosa of the small intestine casually observed by endoscopy. The white appearance of the mucosa was limited to the villi. As demonstrated by light and transmission electron microscopy this was caused by fat loaded enterocytes similar to the picture of abetalipoproteinemia. Fasting serum lipids and apolipoproteins were only if the lower norm level for some parameters, but no increase of the serum lipids was observed after an oral fat load. Because of the missing symptoms, the typical histomorphology and laboratory findings the snow white mucosa of the small intestine is due by the hetocygote form of the autosomal dominant hypobetalipoproteinemia with fat loaded enterocytes.