Lipid storage myopathy, ichthyosis, and steatorrhea

ABHD5-A Regulator of Lipid Metabolism Essential for Diverse Cellular Functions

The α/β-Hydrolase domain-containing protein 5 (ABHD5; also known as comparative gene identification-58, or CGI-58) is the causative gene of the Chanarin-Dorfman syndrome (CDS), a disorder mainly characterized by systemic triacylglycerol accumulation and a severe defect in skin barrier function. The clinical phenotype of CDS patients and the characterization of global and tissue-specific ABHD5-deficient mouse strains have demonstrated that ABHD5 is a crucial regulator of lipid and energy homeostasis in various tissues. Although ABHD5 lacks intrinsic hydrolase activity, it functions as a co-activating enzyme of the patatin-like phospholipase domain-containing (PNPLA) protein family that is involved in triacylglycerol and glycerophospholipid, as well as sphingolipid and retinyl ester metabolism. Moreover, ABHD5 interacts with perilipins (PLINs) and fatty acid-binding proteins (FABPs), which are important regulators of lipid homeostasis in adipose and non-adipose tissues. This review focuses on the multifaceted role of ABHD5 in modulating the function of key enzymes in lipid metabolism.

Chanarin-Dorfman Syndrome: A comprehensive review

The Chanarin-Dorfman syndrome (CDS) is a rare, autosomal recessively inherited genetic disease. This syndrome is associated with a decrease in the lipolysis activity in multiple tissue cells because of recessive mutations in the abhydrolase domain containing 5 (ABHD5) gene, which leads to the accumulation of lipid droplets in multiple types of cells. Major clinical symptoms in patients with CDS include ichthyosis and intracytoplasmic lipid droplets. The variability of clinical symptoms in patients with CDS depends on a large number of mutations involved. In this syndrome, liver involvement is an important cause of mortality and morbidity. This review aims to summarize the demographic characteristic, clinical symptoms, liver involvement and mutations in CDS patients in the literature to date.

CGI-58: Versatile Regulator of Intracellular Lipid Droplet Homeostasis

Comparative gene identification-58 (CGI-58), also known as α/β-hydrolase domain-containing 5 (ABHD5), is a member of a large family of proteins containing an α/β-hydrolase-fold. CGI-58 is well-known as the co-activator of adipose triglyceride lipase (ATGL), which is a key enzyme initiating cytosolic lipid droplet lipolysis. Mutations in either the human CGI-58 or ATGL gene cause an autosomal recessive neutral lipid storage disease, characterized by the excessive accumulation of triglyceride (TAG)-rich lipid droplets in the cytoplasm of almost all cell types. CGI-58, however, has ATGL-independent functions. Distinct phenotypes associated with CGI-58 deficiency commonly include ichthyosis (scaly dry skin), nonalcoholic steatohepatitis, and hepatic fibrosis. Through regulated interactions with multiple protein families, CGI-58 controls many metabolic and signaling pathways, such as lipid and glucose metabolism, energy balance, insulin signaling, inflammatory responses, and thermogenesis. Recent studies have shown that CGI-58 regulates the pathogenesis of common metabolic diseases in a tissue-specific manner. Future studies are needed to molecularly define ATGL-independent functions of CGI-58, including the newly identified serine protease activity of CGI-58. Elucidation of these versatile functions of CGI-58 may uncover fundamental cellular processes governing lipid and energy homeostasis, which may help develop novel approaches that counter against obesity and its associated metabolic sequelae.

Neutral Lipid Storage Diseases as Cellular Model to Study Lipid Droplet Function

Neutral lipid storage disease with myopathy (NLSDM) and with ichthyosis (NLSDI) are rare autosomal recessive disorders caused by mutations in the PNPLA2 and in the ABHD5/CGI58 genes, respectively. These genes encode the adipose triglyceride lipase (ATGL) and α-β hydrolase domain 5 (ABHD5) proteins, which play key roles in the function of lipid droplets (LDs). LDs, the main cellular storage sites of triacylglycerols and sterol esters, are highly dynamic organelles. Indeed, LDs are critical for both lipid metabolism and energy homeostasis. Partial or total PNPLA2 or ABHD5/CGI58 knockdown is characteristic of the cells of NLSD patients; thus, these cells are natural models with which one can unravel LD function. In this review we firstly summarize genetic and clinical data collected from NLSD patients, focusing particularly on muscle, skin, heart, and liver damage due to impaired LD function. Then, we discuss how NLSD cells were used to investigate and expand the current structural and functional knowledge of LDs.

Lipid storage myopathies: Current treatments and future directions

Lipid storage myopathies (LSMs) are a heterogeneous group of genetic disorders that present with abnormal lipid storage in multiple body organs, typically muscle. Patients can clinically present with cardiomyopathy, skeletal muscle weakness, myalgia, and extreme fatigue. An early diagnosis is crucial, as some LSMs can be managed by simple nutraceutical supplementation. For example, high dosage l-carnitine is an effective intervention for patients with Primary Carnitine Deficiency (PCD). This review discusses the clinical features and management practices of PCD as well as Neutral Lipid Storage Disease (NLSD) and Multiple Acyl-CoA Dehydrogenase Deficiency (MADD). We provide a detailed summary of current clinical management strategies, highlighting issues of high-risk contraindicated treatments with case study examples not previously reviewed. Additionally, we outline current preclinical studies providing disease mechanistic insight. Lastly, we propose that a number of other conditions involving lipid metabolic dysfunction that are not classified as LSMs may share common features. These include Neurofibromatosis Type 1 (NF1) and autoimmune myopathies, including Polymyositis (PM), Dermatomyositis (DM), and Inclusion Body Myositis (IBM).

Muscle-specific deletion of comparative gene identification-58 (CGI-58) causes muscle steatosis but improves insulin sensitivity in male mice

Intramyocellular accumulation of lipids is often associated with insulin resistance. Deficiency of comparative gene identification-58 (CGI-58) causes cytosolic deposition of triglyceride (TG)-rich lipid droplets in most cell types, including muscle due to defective TG hydrolysis. It was unclear, however, whether CGI-58 deficiency-induced lipid accumulation in muscle influences insulin sensitivity. Here we show that muscle-specific CGI-58 knockout mice relative to their controls have increased glucose tolerance and insulin sensitivity on a Western-type high-fat diet, despite TG accumulation in both heart and oxidative skeletal muscle and cholesterol deposition in heart. Although the intracardiomyocellular lipid deposition results in cardiac ventricular fibrosis and systolic dysfunction, muscle-specific CGI-58 knockout mice show increased glucose uptake in heart and soleus muscle, improved insulin signaling in insulin-sensitive tissues, and reduced plasma concentrations of glucose, insulin, and cholesterol. Hepatic contents of TG and cholesterol are also decreased in these animals. Cardiac steatosis is attributable, at least in part, to decreases in cardiac TG hydrolase activity and peroxisome proliferator-activated receptor-α/peroxisome proliferator-activated receptor-γ coactivator-1-dependent mitochondrial fatty acid oxidation. In conclusion, muscle CGI-58 deficiency causes cardiac dysfunction and fat deposition in oxidative muscles but induces a series of favorable metabolic changes in mice fed a high-fat diet.

Intestinal Cgi-58 deficiency reduces postprandial lipid absorption

Comparative Gene Identification-58 (CGI-58), a lipid droplet (LD)-associated protein, promotes intracellular triglyceride (TG) hydrolysis in vitro. Mutations in human CGI-58 cause TG accumulation in numerous tissues including intestine. Enterocytes are thought not to store TG-rich LDs, but a fatty meal does induce temporary cytosolic accumulation of LDs. Accumulated LDs are eventually cleared out, implying existence of TG hydrolytic machinery in enterocytes. However, identities of proteins responsible for LD-TG hydrolysis remain unknown. Here we report that intestine-specific inactivation of CGI-58 in mice significantly reduces postprandial plasma TG concentrations and intestinal TG hydrolase activity, which is associated with a 4-fold increase in intestinal TG content and large cytosolic LD accumulation in absorptive enterocytes during the fasting state. Intestine-specific CGI-58 knockout mice also display mild yet significant decreases in intestinal fatty acid absorption and oxidation. Surprisingly, inactivation of CGI-58 in intestine significantly raises plasma and intestinal cholesterol, and reduces hepatic cholesterol, without altering intestinal cholesterol absorption and fecal neutral sterol excretion. In conclusion, intestinal CGI-58 is required for efficient postprandial lipoprotein-TG secretion and for maintaining hepatic and plasma lipid homeostasis. Our animal model will serve as a valuable tool to further define how intestinal fat metabolism influences the pathogenesis of metabolic disorders, such as obesity and type 2 diabetes.

The important role of epidermal triacylglycerol metabolism for maintenance of the skin permeability barrier function

Survival in a terrestrial, dry environment necessitates a permeability barrier for regulated permeation of water and electrolytes in the cornified layer of the skin (the stratum corneum) to minimize desiccation of the body. This barrier is formed during cornification and involves a cross-linking of corneocyte proteins as well as an extensive remodeling of lipids. The cleavage of precursor lipids from lamellar bodies by various hydrolytic enzymes generates ceramides, cholesterol, and non-esterified fatty acids for the extracellular lipid lamellae in the stratum corneum. However, the important role of epidermal triacylglycerol (TAG) metabolism during formation of a functional permeability barrier in the skin was only recently discovered. Humans with mutations in the ABHD5/CGI-58 (α/β hydrolase domain containing protein 5, also known as comparative gene identification-58, CGI-58) gene suffer from a defect in TAG catabolism that causes neutral lipid storage disease with ichthyosis. In addition, mice with deficiencies in genes involved in TAG catabolism (Abhd5/Cgi-58 knock-out mice) or TAG synthesis (acyl-CoA:diacylglycerol acyltransferase-2, Dgat2 knock-out mice) also develop severe skin permeability barrier dysfunctions and die soon after birth due to increased dehydration. As a result of these defects in epidermal TAG metabolism, humans and mice lack ω-(O)-acylceramides, which leads to malformation of the cornified lipid envelope of the skin. In healthy skin, this epidermal structure provides an interface for the linkage of lamellar membranes with corneocyte proteins to maintain permeability barrier homeostasis. This review focuses on recent advances in the understanding of biochemical mechanisms involved in epidermal neutral lipid metabolism and the generation of a functional skin permeability barrier. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Deficiency of liver Comparative Gene Identification-58 causes steatohepatitis and fibrosis in mice

Triglyceride (TG) accumulation in hepatocytes (hepatic steatosis) preludes the development of advanced nonalcoholic fatty liver diseases (NAFLDs) such as steatohepatitis, fibrosis, and cirrhosis. Mutations in human Comparative Gene Identification-58 (CGI-58) cause cytosolic TG-rich lipid droplets to accumulate in almost all cell types including hepatocytes. However, it is unclear if CGI-58 mutation causes hepatic steatosis locally or via altering lipid metabolism in other tissues. To directly address this question, we created liver-specific CGI-58 knockout (LivKO) mice. LivKO mice on standard chow diet displayed microvesicular and macrovesicular panlobular steatosis, and progressed to advanced NAFLD stages over time, including lobular inflammation and centrilobular fibrosis. Compared with CGI-58 floxed control littermates, LivKO mice showed 8-fold and 52-fold increases in hepatic TG content, which was associated with 40% and 58% decreases in hepatic TG hydrolase activity at 16 and 42 weeks, respectively. Hepatic cholesterol also increased significantly in LivKO mice. At 42 weeks, LivKO mice showed increased hepatic oxidative stress, plasma aminotransferases, and hepatic mRNAs for genes involved in fibrosis and inflammation, such as α-smooth muscle actin, collagen type 1 α1, tumor necrosis factor α, and interleukin-1β. In conclusion, CGI-58 deficiency in the liver directly causes not only hepatic steatosis but also steatohepatitis and fibrosis.

Neutral lipid storage disease with subclinical myopathy due to a retrotransposal insertion in the PNPLA2 gene

An 18-year-old girl referred to a rheumatologist with malar flush and Gottran papules was found to have a markedly elevated serum CK. She was a good student and an avid ballet dancer. A muscle biopsy showed massive triglyceride storage, which was also found in peripheral blood granulocytes (Jordan anomaly) and cultured skin fibroblasts. Assessment using computerized dynamometry and cycle ergometry showed normal strength and muscle energetics, but proton spectroscopy revealed severe triglyceride accumulation in both skeletal and cardiac muscle. Sequencing of PNPLA2, the gene responsible for neutral lipid storage disease with myopathy (NLSDM), revealed a retrotransposal insertion of about 1.8kb in exon 3 that abrogates transcription of PNPLA2. The sequences of CGI-58, the gene responsible for Chanarin-Dorfman syndrome (CDS), another multisystem triglyceride storage disease, and of two genes encoding lipid droplets-associated proteins, perilipin A and adipophilin, were normal. This case shows that NLSDM can be a transposon-associated disease and that massive lipid storage in muscle can present as asymptomatic hyperCKemia.

Opposed-phase MR imaging of lipid storage myopathy in a case of Chanarin-Dorfman disease

Chanarin-Dorfman disease (CDD) is a rare genetic disorder characterized by ichthyosis, myopathy, central nervous system disturbances, and intracellular lipid storage in muscle fibers, hepatocytes, and granulocytes. We describe skeletal muscle magnetic resonance imaging findings in a case of CDD, outlining the potential role of GE T1-weighted opposed-phase sequence (chemical shift imaging) in the evaluation of lipid storage myopathies.

Clinical and genetic characterization of Chanarin-Dorfman syndrome

We describe the clinical features, muscle pathology features, and molecular studies of seven patients with Chanarin-Dorfman syndrome (CDS) or neutral lipid storage disease and ichthyosis (NLSDI), a multisystem triglyceride storage disease with massive accumulation of lipid droplets in muscle fibers. All patients presented with congenital ichthyosiform erythroderma, cytoplasmic lipid droplets in blood cells, mild to severe hepatomegaly, and increased serum CK levels and liver enzymes. Three patients showed muscle symptoms and three had steathorrea. Molecular analysis identified five mutations, three of which are novel. These findings expand the clinical and mutational spectrum and underline the genetic heterogeneity of this disease.

Rickets with Dorfman-Chanarin syndrome

BACKGROUND

Dorfman-Chanarin syndrome is a rare, autosomal recessive, inherited, lipid storage disease. It is characterized by nonbullous congenital ichthyosiform erythroderma, leukocyte vacuoles and variable involvement of the liver, muscles and central nervous system, due to errors of triacylglycerol metabolism. To date only 32 cases of this syndrome have been described worldwide.

AIMS

To report the case of a boy with Dorfman-Chanarin syndrome with rickets.

CASE REPORT

A boy of Turkish origin was born of a nonconsanguineous marriage after an uncomplicated perinatal period. On examination the patient had failure to thrive, diffuse erythroderma and ichthyosis and clinical features suggesting rickets. A light-microscopic examination of peripheral smear revealed vacuolated leukocytes typical of Jordans' anomaly. Lipid analysis showed an increase in triacylglycerol and very low density lipoprotein. A radiographic study of the wrist revealed rickets.

CONCLUSION

The clinical progression in these patients ranges from mild to fatal. We believe that patients with ichthyosis should be evaluated bearing in mind the possibility of Dorfman-Chanarin syndrome. This may increase the number of reported Dorfman-Chanarin syndrome cases, and the pathogenesis and progression of the disease will become clearer.

Mutations in CGI-58, the gene encoding a new protein of the esterase/lipase/thioesterase subfamily, in Chanarin-Dorfman syndrome

Chanarin-Dorfman syndrome (CDS) is a rare autosomal recessive form of nonbullous congenital ichthyosiform erythroderma (NCIE) that is characterized by the presence of intracellular lipid droplets in most tissues. We previously localized a gene for a subset of NCIE to chromosome 3 (designated "the NCIE2 locus"), in six families. Lipid droplets were found in five of these six families, suggesting a diagnosis of CDS. Four additional families selected on the basis of a confirmed diagnosis of CDS also showed linkage to the NCIE2 locus. Linkage-disequilibrium analysis of these families, all from the Mediterranean basin, allowed us to refine the NCIE2 locus to an approximately 1.3-Mb region. Candidate genes from the interval were screened, and eight distinct mutations in the recently identified CGI-58 gene were found in 13 patients from these nine families. The spectrum of gene variants included insertion, deletion, splice-site, and point mutations. The CGI-58 protein belongs to a large family of proteins characterized by an alpha/beta hydrolase fold. CGI-58 contains three sequence motifs that correspond to a catalytic triad found in the esterase/lipase/thioesterase subfamily. Interestingly, CGI-58 differs from other members of the esterase/lipase/thioesterase subfamily in that its putative catalytic triad contains an asparagine in place of the usual serine residue.

Dorfman-Chanarin syndrome: a case with prevalent hepatic involvement

BACKGROUND/AIMS

Dorfman-Chanarin syndrome is a very rare condition determined by an autosomal recessive inherited disorder of neutral lipid metabolism. The syndrome is defined by the association of ichthyosiform nonbullous erythroderma, vacuoles in the leukocytes and variable involvement of liver, muscle and central nervous system. Only 19 cases have been described worldwide.

METHODS

We studied a 16-year-old patient with congenital ichthyosis, liver and spleen enlargement and abnormal gamma-glutamyltransferase. Liver biopsy, skin biopsy and blood smear showed abnormal intracellular neutral lipid storage.

RESULTS/CONCLUSION

On the basis of clinical and histological findings, the patient was diagnosed as having Dorfman-Chanarin syndrome. This is the fourth reported Italian case, with a prominent skin and hepatic involvement. Liver biopsy, performed in the first instance, was of great importance in reaching a diagnosis.

Dorfman-Chanarin syndrome (neutral lipid storage disease). A case report

We describe the case of a woman from a small town in the south of Spain, with consanguineous parents, who presented with the complete syndrome. The main clinicopathological characteristics are discussed.

Neutral lipid storage disease: a possible functional defect in phospholipid- linked triacylglycerol metabolism

Neutral lipid storage disease (NLSD) (Chanarin-Dorfman Syndrome) is an autosomal recessive disorder of multisystem triacylglycerol (TAG) storage. Previous work has pointed to a defect in intracellular TAG metabolism. In the studies reported here, the lipid metabolism of three lines of NLSD fibroblasts were compared to normal skin fibroblasts. When pulsed with [3H]oleic acid, the earliest observed abnormality in NLSD cell lines was increased incorporation into phosphatidylethanolamine, followed by accumulation of radiolabel in TAG. Activities of several glycerolipid synthetic enzymes were comparable in NLSD and normal fibroblast lines, excluding oversynthesis of glycerolipid. The proportion of plasmalogen and neutral ether lipid synthesized was normal and alkylglycerols did not accumulate, excluding a defect in ether lipid metabolism. Activities of both acid lipase and Mn2(+)-sensitive lipase within the particulate fractions of NLSD and normal fibroblasts were comparable. These studies are most consistent with functional deficiency of a TAG lipase with activity against a pool of TAG that are normally utilized for phospholipid biosynthesis.

Adult onset lipid storage in gastric mucosa and skeletal muscle fibers associated with gastric pain, progressive muscle weakness and partial deficiency of cytochrome C oxidase

We report on the first case, a 21-year-old man, with partial deficiency of cytochrome c oxidase, lipid storage myopathy and concomitant lipid storage in the gastric mucosa affecting chief, parietal, and argentaffine cells as well as interstitial macrophages. The clinical symptoms consisted of increasing muscle weakness, cramps of the legs, and severe gastric pain that was resistant to treatment. Muscle biopsy specimens showed severe lipid storage in muscle fibers. Enzyme histochemistry revealed partial deficiency of cytochrome c oxidase (COX) with scattered non-reactive fibers among a majority of COX-positive fibers whereas biochemical analysis of muscle homogenates resulted in no corresponding defect of mitochondrial enzymes. Gastric biopsy specimens showed similarly to muscle fibers an extensive accumulation of lipid droplets in the chief cells, HCl producing parietal cells, macrophages, neutrophilic and eosinophilic leucocytes, and to a lesser degree also in argentaffine cells and unmyelinated axons of the gastric mucosa. The lipid droplets were associated with an insignificant increase in the number and size of mitochondria although paracristalline mitochondrial inclusions were neither noted in muscle fibers nor in cells of the gastric mucosa. These findings resemble those in multisystem triglyceride storage disease although the clinical signs were not reminiscent of this disease, and indicate that among the clinically heterogeneous group of cytochrome c oxidase deficiencies lipid storage may not be confined to muscle, but can affect the gastric mucosa as well.

Neutral lipid storage disease with ichthyosis: serum apolipoprotein levels and cholesterol metabolism in monocyte-derived macrophages

Neutral lipid storage disease with ichthyosis (NLSDI) is an inherited metabolic disorder characterized by accumulation of neutral lipids, in a wide variety of cells, by a still unknown mechanism. Previous studies have shown normal cholesterol content in NLSDI granulocytes, fibroblasts and skin cells. Monocyte-derived macrophages possess an additional pathway of cholesterol uptake, which is not shared by these cells and which is not regulated by intracellular cholesterol levels. This pathway is thought to play a rôle in the process of atherosclerosis. Three NLSDI patients were studied. The serum levels of triglycerides, cholesterol, high-density lipoprotein cholesterol, and apolipoproteins A-I and B were within normal limits in all three patients. The intracellular levels of free and esterified cholesterol were measured in the monocyte-derived macrophages of one patient and found to be normal, while the triglyceride concentrations were twice as high as normal. The cholesterol esterification rates, which serve as a sensitive indicator of intracellular changes in cholesteryl ester levels, were normal in the monocyte-derived macrophages of all three patients. These findings provide further evidence that cholesterol metabolism is not disturbed in NLSDI, and it may be inferred that in this respect these patients are not at increased risk for atherosclerosis.

Primary lipid cardiomyopathy

In this communication, we describe an isolated, apparently congenital cardiomyopathy (CMP) characterized by the accumulation of stainable lipid in mitochondria of cardiomyocytes. This lesion, which we term primary lipid cardiomyopathy, has not been reported so far. The structural alteration was associated with progressive heart failure, leading to death at the age of 3 years, and with massive hypertrophy of myocardium. Lipid storage in heart muscle cells resulted in an impressive yellow to orange color of the myocardium. We suggest that this type of primary CMP may represent a new member within the group of mitochondrial CMPs. Possible pathogenic mechanisms are discussed.

Ichthyosis and neutral lipid storage disease (Dorfman-Chanarin syndrome)

Ichthyosis and neutral lipid storage disease (INLSD) is a nonlysosomal, multisystemic, triglyceride storage disorder. It is characterized by nonbullous congenital ichthyosiform erythroderma (NBCIE), leukocyte vacuoles, and variable involvement of the liver, muscles, eyes, and central nervous system. In our patient fat-containing vacuoles were also demonstrated in the epidermis. In patients with NBCIE, the diagnosis of INLSD is readily made by direct examination of a peripheral blood smear demonstrating cytoplasmic lipid vacuoles within most granulocytes and monocytes.

Systemic triglyceride storage disease with normal carnitine: a putative defect in long-chain fatty acid metabolism

A 45-year-old Japanese man presented with lipid storage myopathy, fatty liver, cardiomyopathy, vacuolated leukocytes (Jordans' anomaly) and perceptive deafness. His parents were consanguineous and his younger sister was also affected. Histopathological and biochemical studies revealed an abnormal accumulation of triglyceride in muscle, liver, leukocytes, gastrointestinal endothelial cells and cultured skin fibroblasts. On electron microscopy, the vacuoles lacked limiting membranes and were adjacent to the mitochondria. Total and free carnitines in muscle were normal levels. Production rate of 14CO2 or acid-soluble [14C]metabolites from [1-14C]palmitate in the patient's cells was decreased to about 50% of that in control cells, whereas that from [1-14C]butyrate was normal. Long-chain fatty acyl esterase activities in the patient's leukocytes were normal at both pH 4.0 and pH 8.0. Despite the strong suggestion of an impaired metabolism of long-chain fatty acids, there were no evidences of abnormalities in carnitine metabolism or uptake of fatty acids into cells. The disorder is clinically different from defects in carnitine metabolism, defects in the carnitine-acylcarnitine translocase system or in mitochondrial beta-oxidation enzymes. Although the underlying metabolic defect has not been elucidated, this disease seems to be an autosomal-recessively inherited disorder of systemic triglyceride storage, probably due to an impaired regulation of lipolysis and triacylglycerol synthesis.

Sjögren-Larsson syndrome. Impaired fatty alcohol oxidation in cultured fibroblasts due to deficient fatty alcohol:nicotinamide adenine dinucleotide oxidoreductase activity

Lipid metabolism was studied in cultured skin fibroblasts from patients with the inherited disorder, Sjögren-Larsson syndrome (SLS). Intact SLS fibroblasts incubated in the presence of [1-14C]palmitate accumulated more radioactive hexadecanol than did normal cells, whereas incorporation of radioactivity into other cellular lipids was unaltered. The hexadecanol content of SLS fibroblasts was abnormally elevated. Hexadecanol accumulation was not due to increased fatty alcohol synthesis nor its deficient utilization for glycerol ether synthesis. The half-life of intracellular hexadecanol loaded into SLS fibroblasts was increased (70 min) compared with normal (15 min), and intact SLS fibroblasts showed impaired oxidation of [14C]-hexadecanol to fatty acid. Fatty alcohol:NAD+ oxidoreductase, the enzyme catalyzing this reaction, was deficient in SLS fibroblasts. Mean total activity in SLS fibroblasts (n = 5) was 13% of that in normal fibroblasts, and palmitoyl CoA-inhibitable activity was 1% of normal. Fibroblasts from two obligate SLS heterozygotes had enzyme activities intermediate between that in normal fibroblasts and individuals with SLS. These results suggest that the primary defect in SLS is deficiency of fatty alcohol:NAD+ oxidoreductase. SLS represents the first inherited disorder in man associated with an isolated abnormality in fatty alcohol metabolism.

Ichthyosis and neutral lipid storage disease

A boy with a lipid storage disease characterized by lamellar ichthyosis, cataracts, hepatosplenomegaly, and leukocyte vacuoles has been identified in a Sicilian family. This patient shows all the characteristics of ichthyosis and neutral lipid storage disease (Chanarin-Dorfman syndrome). Family data confirm an autosomal recessive inheritance; the heterozygotes may be detected by the presence of vacuoles in circulating eosinophils.

Neutral lipid storage disease with ichthyosis: lipid content and metabolism of fibroblasts

Neutral lipid storage disease with ichthyosis is a newly recognized heritable disorder characterized by widespread cellular triglyceride storage. Lipid metabolism in fibroblasts cultured from three affected family members was studied. The stored lipid is triglyceride composed of an unremarkable fatty acid profile and derived from both exogenously-supplied and endogenously-synthesized fatty acids. Lipid storage could not be corrected by prolonged culture in lipid-depleted media. Acetyl CoA carboxylase activity and beta-oxidation of palmitate were both normal. Taken together, these studies exclude a primary defect of fatty acid uptake, over-synthesis or impaired beta-oxidation. Moreover, triacylglycerol lipase activity of homogenates of fibroblasts from patients with NLSDI examined over the range of pH 3.5-8.5 was normal.

Dorfman-Chanarin syndrome. A case report and a review

Dorfman-Chanarin syndrome in two sisters of Jewish Iraqi origin is reported. This heritable disorder of the metabolism of neutral lipids was manifested by congenital ichthyosis, vacuoles in the leukocytes, and variable involvement of liver, muscle, central nervous system, and the auditory system. In two asymptomatic members of the family leukocyte vacuoles were found as the only sign of the syndrome. Clinical, pathologic, ultrastructural, and biochemical findings are described. Previous reported cases are reviewed.

Changes in oleic acid oxidation and incorporation into lipids of differentiating L6 myoblasts cultured in normal or fatty acid-supplemented growth medium

L6 myoblasts accumulate large stores of neutral lipid (predominantly triacylglycerol) when cultured in fatty acid-supplemented growth medium. No accumulation of neutral lipid was evident in myotubes (differentiated myoblasts) when treated similarly. Triacylglycerol accumulation was rapid and dependent on exogenous fatty acid concentration. Triacylglycerol content in myoblasts cultured in fatty acid-supplemented growth medium was approx. 3-fold higher than that in myotubes treated similarly and 2-3-fold higher than that in myoblasts cultured in normal growth medium. Incorporation studies using [I-14C]oleic acid showed that myoblasts and myotubes take up exogenous fatty acid at similar rates. However, cells cultured in fatty acid-supplemented growth medium remove more exogenous fatty acid than do cells cultured in normal growth medium. Over 90% of the incorporated label was found in phospholipid and triacylglycerol fractions in all situations studied. Myoblasts incorporated a more significant proportion (P less than 0.001) of label into triacylglycerol compared with that of myotubes. No differences in fatty acid oxidation rates were detected when differentiating L6 cells cultured in normal growth medium were compared with those cultured in fatty acid-supplemented growth medium. However, fatty acid oxidation rates were observed to increase 3-5-fold upon myoblast differentiation. We conclude that there is a marked change in the pattern of lipid metabolism when myoblasts (primarily triacylglycerol-synthesizing cells) differentiate into myotubes (primarily phospholipid-synthesizing cells). Understanding these changes, which coincide with normal muscle development, may be important, since a defect in this natural switch could explain the observed accumulation of lipid in muscle characteristic of some of the muscular dystrophies and other lipid-storage myopathies.

Metabolism of neutral lipids in cultured fibroblasts from multisystemic (or type 3) lipid storage myopathy

The lipid metabolism in cultured fibroblasts from multisystemic (type 3) lipid storage myopathy (MLSM) and controls has been studied through pulse-chase experiments using radiolabelled oleic acid and acetate precursors. The uptake of radiolabelled oleic acid by MLSM fibroblasts was slightly higher than in controls but did not seem to be the primary defect of the multisystemic lipid storage myopathy. The uptake of radiolabelled acetate was quite similar in MLSM and in control cells. During short-time pulse periods, using either radiolabelled oleic acid or acetate as precursors, we observed no significant difference in lipid composition between MLSM and controls. In contrast, pulse experiments using radiolabelled oleic acid as precursor showed a major accumulation of radiolabelled triacylglycerols in MLSM (around 1000% of controls); no significant increase of other neutral or polar lipids was noticed. A similar triacylglycerol storage was observed by using radiolabelled acetate as precursor, but in this case the difference between MLSM and controls was more pronounced; we also observed in MLSM cells a higher amount of polar lipids which can be due to an increased rate of fatty acid biosynthesis (from radiolabelled acetate). Chase experiments, after pulse by low concentration of exogenous radiolabelled oleic acid or acetate, showed similar features: the biosynthesized triacylglycerols were not at all degraded in MLSM, but on the contrary increased, probably by accumulation of radiolabelled triacylglycerols newly synthesized from radiolabelled fatty acids liberated during the phospholipid turnover. Similarly, the triacylglycerol storage induced by high doses of fatty acids was not degraded in MLSM cells, in contrast to control cells. This suggested that the triacylglycerols synthesized in the presence of low and high levels of fatty acids were accumulated in only one subcellular cytoplasmic compartment without relationship with the lysosomal compartment, since these cells were not deficient in acid lysosomal lipase. The more probable hypothesis is a deficiency of the cytoplasmic catabolism of triacylglycerols in MLSM cells.

Tissue culture studies of muscle disorders: Part 2. Biochemical studies, nerve-muscle culture, metabolic myopathies, and animal models

This review continues with studies of protein, lipid, and purine metabolism of Duchenne muscular dystrophy (DMD) cells in vitro and of muscle cells in combined culture with nerve cells. In vitro studies of human metabolic myopathies are tabulated. Results using the hamster, chicken, and mouse (dy25, dy, mdg, and mdx) myopathies are discussed. Interesting findings include suggestions of altered collagen synthesis by DMD cells. Analysis of cell proteins by two-dimensional gel electrophoresis and the use of combined nerve-muscle cultures remain important areas of development. It is disappointing that so few attempts have been made to repeat significant findings in this field, and when a number of laboratories have examined the same phenomenon, the results are often contradictory. It remains to be shown how these various abnormalities found in cells in vitro are related to each other and to those pathologic features of diseased muscle observed in vivo.

Ichthyosis and neutral lipid storage disease

Four members of a consanguineous middle eastern family had a lipid storage disease characterized by congenital ichthyosiform erythroderma, neurosensory deafness, cataracts, mild myopathy, and leukocyte vacuoles. These patients are similar to several others recently reported and represent a unique disorder of lipid metabolism. The clinical and biochemical manifestations of this lipid storage disease are reviewed. Evidence is presented that the disorder is inherited as an autosomal recessive trait, and that heterozygotes may be detected by the presence of vacuoles within circulating eosinophils.

The ichthyoses--pathogenesis and prenatal diagnosis: a review of recent advances

Disturbances in the process of normal cornification leading to pathologic scaling provide the pathophysiologic basis for the ichthyoses. These disturbances may result from either abnormalities in protein metabolism (keratinization) (i.e., the "bricks") or in lipid metabolism (i.e., the "mortar") (Fig. 1). The evidence linking the various ichthyoses to defects in protein or lipid metabolism have been reviewed. It is likely that future advances will lead not only to a more complete understanding of the pathogenesis of these disorders, but also will shed significant light on the normal stratum corneum functions of barrier formation and desquamation, as well as lead the way to more rational and effective therapies. In recent years, prenatal diagnosis has been successfully performed in several of the ichthyoses. It is likely that improvements in our ability to prenatally diagnose those disorders will advance hand-in-hand with further progress in unraveling their underlying causes.

Fatal lipid storage myopathy with deficiency of cytochrome-c-oxidase and carnitine. A contribution to the combined cytochemical-finestructural identification of cytochrome-c-oxidase in longterm frozen muscle

Two newborn female siblings fell ill with apathy, failure of suckling and a generalized progressive muscular hypotonia. Death occured at the age of 7 weeks, obviously caused by impairment of respiratory musculature. Biochemical studies in one child revealed carnitine deficiency especially in skeletal muscle; hepatic encephalopathy was absent. Both children had a generalized hyperaminoaciduria, an unusual finding in primary carnitine deficiency. Besides fatty metamorphosis of the liver, bilateral hydroureters and tubular calcifications of both kidneys, morphological studies showed a generalized lipid storage myopathy which predominated in Type-I-fibres and was accentuated in the muscles of the neck. Enzymehistochemical electron microscopy in longterm frozen muscle demonstrated that cytochrome-c-oxidase activity was absent not only in myopathic but also in most of the morphological unchanged muscle fibres. Only some fibres and endothelial cells displayed normal activity of mitochondria. Biochemically no cytochrome aa3 (cytochrome-c-oxidase) could be found in skeletal muscle; cytochrome b was almost undetectable. --In newborns with fatal lipid storage myopathy and carnitine deficiency it seems necessary to look for additional defects in the respiratory chain. Enzyme histochemical electron microscopy is a sensitive method in identifying cytochrome-c-oxidase even after a 12 months period of storage.

Disorders of lipid metabolism in muscle

At rest and during sustained exercise, lipids are the main source of energy for muscle. Free fatty acids become available to muscle from plasma free fatty acids and triglycerides, and from intracellular triglycride lipid droplets. Transport of long-chain fatty acyl groups into the mitochondria requires esterification and de-esterification with carnitine by the "twin" enzymes carnitine palmityltransferase (CPT) I and II, bound to the outer and inner faces of the inner mitochondrial membrane. Carnitine deficiency occurs in two clinical syndromes. (1) In the myopathic form, there is weakness; muscle biopsy shows excessive accumulation of lipid droplets; and the carnitine concentration is markedly decreased in muscle but normal in plasma. (2) In the systemic form, there are weakness and recurrent episodes of hepatic encephalopathy; muscle biopsy shows lipid storage; and the carnitine concentration is decreased in muscle, liver, and plasma. The etiology of carnitine deficiency is not known in either the myopathic or the systemic form, but administration of carnitine or corticosteroids has been beneficial in some patients. "Secondary" carnitine deficiency may occur in patients with malnutrition, liver disease, chronic hemodialysis, and, possibly, mitochondrial disorders. CPT deficiency causes recurrent myoglobinuria, usually precipitated by prolonged exercise or fasting. Muscle biopsy may be normal or show varying degrees of lipid storage. Genetic transmission is probably autosomal recessive, but the great male predominance (20/21) remains unexplained. In many cases, lipid storage myopathy is not accompanied by carnitine or CPT deficiency, and the biochemical error remains to be identified.