Abetalipoproteinemia (Bassen-Kornzweig syndrome). Muscle involvement

A tale of 2 cousins: An atypical and a typical case of abetalipoproteinemia

Abetalipoproteinemia (ABL) is a rare recessive genetic disease caused by mutations of the MTTP gene. This disease is characterised by a defect in the lipidation of APO B and the absence of VLDL and chylomicron production. Patients affected by ABL present neurological, hemalogical and gastro-intestinal symptoms due to deficiency in lipophilic vitamins and fat malabsorption. We herein report the case of two cousins, one presenting classical symptoms of abetalipoproteinemia and one presenting a much attenuated phenotype. The proband carried a novel combination of MTTP mutations, the 1867+1G>A and the R540C mutations. This patient never received any vitamin supplements and was relatively free of symptoms despite an undetectable APO B concentration. Her cousin was homozygous for 1867+1G>A MTTP mutation and presented most of the classical symptoms of ABL. In conclusion we report a very unusual kindred where on affected member is strongly symptomatic of ABL whereas the other presents very mostly asymptomatic disease suggesting that ABL can present itself with a very incomplete clinical penetrance.

Insights from human congenital disorders of intestinal lipid metabolism

The intestine must challenge the profuse daily flux of dietary fat that serves as a vital source of energy and as an essential component of cell membranes. The fat absorption process takes place in a series of orderly and interrelated steps, including the uptake and translocation of lipolytic products from the brush border membrane to the endoplasmic reticulum, lipid esterification, Apo synthesis, and ultimately the packaging of lipid and Apo components into chylomicrons (CMs). Deciphering inherited disorders of intracellular CM elaboration afforded new insight into the key functions of crucial intracellular proteins, such as Apo B, microsomal TG transfer protein, and Sar1b GTPase, the defects of which lead to hypobetalipoproteinemia, abetalipoproteinemia, and CM retention disease, respectively. These "experiments of nature" are characterized by fat malabsorption, steatorrhea, failure to thrive, low plasma levels of TGs and cholesterol, and deficiency of liposoluble vitamins and essential FAs. After summarizing and discussing the functions and regulation of these proteins for reader's comprehension, the current review focuses on their specific roles in malabsorptions and dyslipidemia-related intestinal fat hyperabsorption while dissecting the spectrum of clinical manifestations and managements. The influence of newly discovered proteins (proprotein convertase subtilisin/kexin type 9 and angiopoietin-like 3 protein) on fat absorption has also been provided. Finally, it is stressed how the overexpression or polymorphism status of the critical intracellular proteins promotes dyslipidemia and cardiometabolic disorders.

Vitamin E deficiency impairs the somatostatinergic receptor-effector system and leads to phosphotyrosine phosphatase overactivation and cell death in the rat hippocampus

Vitamin E plays an essential role in maintaining the structure and function of the nervous system, and its deficiency, commonly associated with fat malabsorption diseases, may reduce neuronal survival. We previously demonstrated that the somatostatinergic system, implicated in neuronal survival control, can be modulated by α-tocopherol in the rat dentate gyrus, increasing cyclic adenosine monophosphate response element binding protein phosphorylation. To gain a better understanding of the molecular actions of tocopherols and examine the link among vitamin E, somatostatin and neuronal survival, we have investigated the effects of a deficiency and subsequent administration of tocopherol on the somatostatin signaling pathway and neuronal survival in the rat hippocampus. No changes in somatostatin expression were detected in vitamin-E-deficient rats. These rats, however, showed a significant increase in the somatostatin receptor density and dissociation constant, which correlated with a significant increase in the protein levels of somatostatin receptors. Nevertheless, vitamin E deficiency impaired the ability of the somatostatin receptors to couple to the effectors adenylyl cyclase and phosphotyrosine phosphatase by diminishing Gi protein functionality. Furthermore, vitamin E deficiency significantly increased phosphotyrosine phosphatase activity and PTPη expression, as well as PKCδ activation, and decreased extracellular-signal-regulated kinase phosphorylation. All these changes were accompanied by an increase in neuronal cell death. Subsequent α-tocopherol administration partially or completely reversed all these values to control levels. Altogether, our results prove the importance of vitamin E homeostasis in the somatostatin receptor-effector system and suggest a possible mechanism by which this vitamin may regulate the neuronal cell survival in the adult hippocampus.

Allele-specific regulation of MTTP expression influences the risk of ischemic heart disease

Promoter polymorphisms in microsomal triglyceride transfer protein (MTTP) have been associated with decreased plasma lipids but an increased risk for ischemic heart disease (IHD), indicating that MTTP influences the susceptibility for IHD independent of plasma lipids. The objective of this study was to characterize the functional promoter polymorphism in MTTP predisposing to IHD and its underlying mechanism. Use of pyrosequencing technology revealed that presence of the minor alleles of the promoter polymorphisms -493G>T and -164T>C result in lower transcription of MTTP in vivo in the heart, liver, and macrophages. In vitro experiments indicated that the minor -164C allele mediates the lower gene expression and that C/EBP binds to the polymorphic region in an allele-specific manner. Furthermore, homozygous carriers of the -164C were found to have increased risk for IHD as shown in a case-control study including a total of 544 IHD patients and 544 healthy control subjects. We concluded that carriers of the minor -164C allele have lower expression of MTTP in the heart, mediated at least partly by the transcription factor CCAAT/enhancer binding protein, and that reduced concentration of MTTP in the myocardium may contribute to IHD upon ischemic damage.

Abetalipoproteinemia: two case reports and literature review

Abetalipoproteinemia (ABL, OMIM 200100) is a rare, autosomal recessive disorder, characterized by fat malabsorption, acanthocytosis and hypocholesterolemia in infancy. Later in life, deficiency of fat-soluble vitamins is associated with development of atypical retinitis pigmentosa, coagulopathy, posterior column neuropathy and myopathy. ABL results from mutations in the gene encoding the large subunit of microsomal triglyceride transfer protein (MTP; OMIM 157147). To date at least 33 MTP mutations have been identified in 43 ABL patients. We describe the clinical progress of two patients, both currently in the fifth decade of life, who were diagnosed with ABL as children and were treated with high oral doses of fat soluble vitamins, including vitamin E over the last three decades. Treatment appears to have been associated with arrest of the neuropathy and other complications in both patients. Because pharmacologic inhibition of MTP is being developed as a novel approach to reduce plasma cholesterol for prevention of cardiovascular disease, defining the long-term clinical features of patients with a natural deficiency in MTP might provide some insight into the possible effects of such treatments. We review the range of clinical, biochemical and molecular perturbations in ABL.

Sarcoplasmic body myopathy--a rare hereditary myopathy with characteristic inclusions

OBJECTIVES

To characterise a Swedish family with a rare hereditary myopathy with unique sarcoplasmic inclusion bodies in the muscle biopsy.

MATERIALS AND METHODS

Part of the pedigree was described in 1980. Nine new members of the included and the phenotype further characterised through clinical, neurophysiological and radiological investigations.

RESULTS

Six of the nine subjects displayed clinical and/or laboratory evidence of myopathy with sarcoplasmic inclusions.

CONCLUSIONS

Sarcoplasmic body myopathy is distinguished from other distal myopathies by a more malignant course and early involvement of thenar muscles and hand flexors. Five to ten years after onset the affected subjects develop distal, as well as proximal, weakness and atrophy and the majority require a wheelchair after ten to fifteen years of disease. The disorder is manifested through elevated creatine kinase levels and the presence of the pathognomonic sarcoplasmic inclusions prior to clinical signs and symptoms.

The role of the microsomal triglygeride transfer protein in abetalipoproteinemia

The microsomal triglyceride transfer protein (MTP) is a dimeric lipid transfer protein consisting of protein disulfide isomerase and a unique 97-kDa subunit. In vitro, MTP accelerates the transport of triglyceride, cholesteryl ester, and phospholipid between membranes. It was recently demonstrated that abetalipoproteinemia, a hereditary disease characterized as an inability to produce chylomicrons and very low-density lipoproteins in the intestine and liver, respectively, results from mutations in the gene encoding the 97-kDa subunit of the microsomal triglyceride transfer protein. Downstream effects resulting from this defect include malnutrition, very low plasma cholesterol and triglyceride levels, altered lipid and protein compositions of membranes and lipoprotein particles, and vitamin deficiencies. Unless treated, abetalipoproteinemic subjects develop gastrointestinal, neurological, ophthalmological, and hematological abnormalities.

Histochemical and ultrastructural pathology of skeletal muscle in a patient with abetalipoproteinemia

Pathological examination was carried out of the skeletal muscle of an 8-year-old boy with abetalipoproteinemia. The patient complained of diarrhea, and showed a deficiency of betalipoprotein, decreased fat-soluble vitamins, acanthocytosis and a mild increase in serum creatine kinase. The prominent histochemical finding was punctate deposits of acid phosphatase activity in most fibers. Ultrastructural lesions revealed a number of giant lysosomes. Although these pathological findings seemed to be related to vitamin E deficiency, other pathological findings such as concentric laminated bodies or filamentous bodies were also observed. The clinical course and the changes in the pathological findings in our patient after long-term vitamin E therapy need to be observed.

[Role of the electrophysiologic examination in the diagnosis of Bassen-Kornzweig syndrome]

An autosomal recessive disorder, abetalipoproteinemia or Bassen-Kornzweig disease, concerning two sisters are described. This disorder, clinically similar to Friedreich ataxia, should be examined by electrophysiological and laboratory procedures because of the possibility of treatment by high doses of vitamin A and E. The routine electrophysiological examination of the two sisters revealed a degenerative spinocerebellar and peripheral nervous process which confirmed the damage of large myelinated fibers, as reported in the literature: neurogenic muscular atrophy of distal muscles, polyphasic motor unit potentials, moderately decrease of lower motor and sensory nerve conduction rates, and reduced amplitude of evoked responses in sensory nerves and muscles. We stress out the diagnostic value of the heterogenous conduction decrease in the distal motor fibers, signs of processes of demyelination or distal regeneration.

Lysosomal storage in human skeletal muscle

Skeletal muscle is involved symptomatically in two lysosomal storage diseases, acid maltase deficiency and a similar condition in which enzyme levels are normal. Asymptomatic storage in skeletal muscle cells is found in Batten-Kufs' disease (ceroid lipofuscinosis), Fabry's disease, and mannosidosis, as well as in rare patients with an unidentified storage disease. Other cell types (vascular endothelium, smooth muscle, fibroblasts, satellite cells) within the confines of the biopsy specimen may reveal storage in other diseases. The differential diagnosis involves predominantly both normal and abnormal conditions in which acid phosphatase activity is prominent in cells.

Progressive neuromuscular disease in children with chronic cholestasis and vitamin E deficiency: clinical and muscle biopsy findings and treatment with alpha-tocopherol

We have studied four children (ages 6 to 17 years) with chronic cholestasis who developed a slowly progressive neuromuscular disease characterized by ataxia, dysmetria, areflexia, loss of vibratory sensation, and a variable ophthalmoplegia. Serum vitamin E concentrations were low in all patients prior to treatment (0.17-2.0 mg/g cholesterol, normal greater than 3 mg/g). Muscle histochemical studies showed prominent yellow autofluorescence, basophilic cytoplasmic inclusions which stain with esterase and acid phosphatase, and occasional necrotic fibers. Ultrastructural findings consisted of increased number and size of membrane-bound dense bodies (lysosomes), membranous whorls, and autophagic vacuoles. Intramuscular injections of all-rac-alpha-tocopherol (0.55-1.42 mg/kg per 24 hours based on individualized pharmacokinetic data) were required in three patients to achieve normal serum vitamin E values. High-dose (32 mg/kg per 24 hours) oral supplementation was effective in one patient. After normalization of serum vitamin E concentrations for 12 to 20 months, the neurologic disease has improved in all four patients.

Progressive neuromuscular disease in children with chronic cholestasis and vitamin E deficiency: diagnosis and treatment with alpha tocopherol

We have studied four children (ages 6 to 17 years) with chronic cholestasis who developed a slowly progressive neuromuscular disease characterized by ataxia, dysmetria, areflexia, loss of vibratory sensation, and a variable ophthalmoplegia. Serum vitamin E concentration were low in all patients prior to treatment. Muscle histochemical studies in all four patients showed autofluorescent basophilic esterase and acid phosphatase-positive cytoplasmic inclusions and occasional necrotic fibers. These distinctive muscle changes are similar to those described in vitamin E-deficient animals. Intramuscular injections of alpha tocopherol were required in three patients to achieve normal serum vitamin E values. High-dose oral supplementation was effective in one patient. After normalization of serum vitamin E concentrations for six to 14 months, the neurologic disease has improved in all four patients.