LMNA, encoding lamin A/C, is mutated in partial lipodystrophy

Insulin stimulation of hepatic triacylglycerol secretion in the insulin-replete state: implications for the etiology of peripheral insulin resistance

Observations on humans, on rats in vivo, and on isolated perfused rat livers indicate that insulin stimulates hepatic very-low-density lipoprotein (VLDL)-TAG secretion when the liver is chronically exposed to the hormone. They suggest that frequent stimulation of insulin secretion throughout the diurnal cycle may result in a chronic stimulation of VLDL secretion and increased delivery of acyl moieties to the periphery, particularly to muscle, the most important site of insulin-sensitive glucose disposal. If acyl groups are provided in excess of the oxidative needs of the tissue, this may lead to induction of insulin resistance, irrespective of whether obesity is established concomitantly. Dietary factors that stimulate hepatic VLDL secretion may have the same effect and contribute to the induction of a vicious spiral leading to the development of the full-blown Metabolic Syndrome and its pathological consequences, including type-2 diabetes, stroke, and cardiovascular disease.

The Ig-like structure of the C-terminal domain of lamin A/C, mutated in muscular dystrophies, cardiomyopathy, and partial lipodystrophy

Lamins are nuclear intermediate filaments that, together with lamin-associated proteins, maintain nuclear shape and provide a structural support for chromosomes and replicating DNA. We have determined the solution structure of the human lamin A/C C-terminal globular domain which contains specific mutations causing four different heritable diseases. This domain encompasses residues 430-545 and adopts an Ig-like fold of type s. We have also characterized by NMR and circular dichroism the structure and thermostability of three mutants, R453W and R482W/Q, corresponding to "hot spots" causing Emery-Dreifuss muscular dystrophy and Dunnigan-type lipodystrophy, respectively. Our structure determination and mutant analyses clearly show that the consequences of the mutations causing muscle-specific diseases or lipodystrophy are different at the molecular level.

Structure of the globular tail of nuclear lamin

The nuclear lamins form a two-dimensional matrix that provides integrity to the cell nucleus and participates in nuclear activities. Mutations in the region of human LMNA encoding the carboxyl-terminal tail Lamin A/C are associated with forms of muscular dystrophy and familial partial lipodystrophy (FPLD). To help discriminate tissue-specific phenotypes, we have solved at 1.4-A resolution the three-dimensional crystal structure of the lamin A/C globular tail. The domain adopts a novel, all beta immunoglobulin-like fold. FPLD-associated mutations cluster within a small surface, whereas muscular dystrophy-associated mutations are distributed throughout the protein core and on its surface. These findings distinguish myopathy- and lipodystrophy-associated mutations and provide a structural framework for further testing hypotheses concerning lamin function.

Defective prelamin A processing and muscular and adipocyte alterations in Zmpste24 metalloproteinase-deficient mice

The mouse ortholog of human FACE-1, Zmpste24, is a multispanning membrane protein widely distributed in mammalian tissues and structurally related to Afc1p/ste24p, a yeast metalloproteinase involved in the maturation of fungal pheromones. Disruption of the gene Zmpste24 caused severe growth retardation and premature death in homozygous-null mice. Histopathological analysis of the mutant mice revealed several abnormalities, including dilated cardiomyopathy, muscular dystrophy and lipodystrophy. These alterations are similar to those developed by mice deficient in A-type lamin, a major component of the nuclear lamina, and phenocopy most defects observed in humans with diverse congenital laminopathies. In agreement with this finding, Zmpste24-null mice are defective in the proteolytic processing of prelamin A. This deficiency in prelamin A maturation leads to the generation of abnormalities in nuclear architecture that probably underlie the many phenotypes observed in both mice and humans with mutations in the lamin A gene. These results indicate that prelamin A is a specific substrate for Zmpste24 and demonstrate the usefulness of genetic approaches for identifying the in vivo substrates of proteolytic enzymes.

The molecular basis of genetic lipodystrophies

OBJECTIVES

Hyperinsulinemia is often associated with a cluster of metabolic abnormalities, which usually presents before the onset of frank diabetes. Lipodystrophy syndromes are frequently associated with hyperinsulinemia and may act as models for insulin resistance. Lipodystrophy is characterized in broad terms by loss of subcutaneous adipose tissue. Despite heterogeneous causes, which include both genetic and acquired forms, lipodystrophy syndromes have similar metabolic attributes, including insulin resistance, hyperlipidemia and diabetes.

RESULTS

Recently, the molecular basis of two genetic forms of lipodystrophy, namely Dunnigan-type familial partial lipodystrophy (FPLD; MIM 151660) and Berardinelli-Seip complete lipodystrophy (BSCL; MIM 269700) have been reported. There is evidence for genetic heterogeneity for both types of lipodystrophy. In addition, murine models of lipodystrophy have provided key insights into alterations of metabolic pathways in lipodystrophy.

CONCLUSIONS

Delineation of the human molecular genetic basis of two distinct forms of inherited lipodystrophy may have relevance for the common insulin resistance syndrome and for acquired lipodystrophy syndromes.

Multisystem dystrophy syndrome due to novel missense mutations in the amino-terminal head and alpha-helical rod domains of the lamin A/C gene

Mutations in different domains of the LMNA (lamin A/C) gene encoding nuclear envelope proteins lamin A and lamin C cause familial partial lipodystrophy (Dunnigan variety), dilated cardiomyopathy, and autosomal dominant forms of Emery-Dreifuss and limb-girdle muscular dystrophies. The objective of this study was to evaluate LMNA variants in two families with familial partial lipodystrophy (Dunnigan variety) who also had cardiac conduction system defects and other manifestations related to cardiomyopathy. We performed mutational analysis of the lamin A/C gene in affected and unaffected subjects by deoxyribonucleic acid sequencing of the exons. Two novel missense mutations were identified in exon 1 of the lamin A/C gene. One mutation, R28W (CGG-->TGG), affected the amino-terminal head domain, and the other, R62G (CGC-->GGC), affected the alpha-helical rod domain. Affected subjects from both families had an increased prevalence of cardiac manifestations, such as atrioventricular conduction defects, atrial fibrillation, and heart failure due to ventricular dilatation, as well as pacemaker implantation. The proband from one of the families also had proximal muscle weakness. Novel genetic defects in the LMNA gene in two families with the Dunnigan variety of familial partial lipodystrophy, cardiac conduction system defects, and other manifestations related to cardiomyopathy suggest the occurrence of a multisystem dystrophy syndrome due to LMNA mutations.

Caspase-6 gene disruption reveals a requirement for lamin A cleavage in apoptotic chromatin condensation

To study the role of caspase-6 during nuclear disassembly, we generated a chicken DT40 cell line in which both alleles of the caspase-6 gene were disrupted. No obvious morphological differences were observed in the apoptotic process in caspase-6- deficient cells compared with the wild type. However, examination of apoptosis in a cell-free system revealed a block in chromatin condensation and apoptotic body formation when nuclei from HeLa cells expressing lamin A or lamin A-transfected Jurkat cells were incubated in caspase-6-deficient apoptotic extracts. Transfection of exogenous caspase-6 into the clone reversed this phenotype. Lamins A and C, which are caspase-6-only substrates, were cleaved by the wild-type and heterozygous apoptotic extracts but not by the extracts lacking caspase-6. Furthermore, the caspase-6 inhibitor z-VEID-fmk mimicked the effects of caspase-6 deficiency and prevented the cleavage of lamin A. Taken together, these observations indicate that caspase-6 activity is essential for lamin A cleavage and that when lamin A is present it must be cleaved in order for the chromosomal DNA to undergo complete condensation during apoptotic execution.

Molecular analysis of Berardinelli-Seip congenital lipodystrophy in Oman: evidence for multiple loci

Congenital generalized lipodystrophy (CGL) is a rare disorder characterized by the absence of body fat and insulin resistance and accompanied by other features, including acanthosis nigricans, organomegaly, hyperandrogenism, and diabetes. We have examined case subjects from 11 families in Oman with CGL. All subjects were the progeny of consanguineous marriages; therefore, a homozygosity mapping strategy was used to investigate the reported loci, 11q13 and 9q34. Three subjects could be linked to 11q13, and mutations were found within the seipin gene. An additional eight subjects were linked to 9q34, but the locus was in a 9-cM interval with no known microsatellites, so further fine mapping was not possible. However, two sibships (four subjects) did not map to either locus, raising the possibility of more than two lipodystrophy loci within the Oman population.

Intracellular trafficking of MAN1, an integral protein of the nuclear envelope inner membrane

MAN1 is an integral protein of the inner nuclear membrane that shares the LEM domain, a conserved globular domain of approximately 40 amino acids, with lamina-associated polypeptide (LAP) 2 and emerin. Confocal immuofluorescence microscopy studies of the intracellular targeting of truncated forms of MAN1 showed that the nucleoplasmic, N-terminal domain is necessary for inner nuclear membrane retention. A protein containing the N-terminal domain with the first transmembrane segment of MAN1 is retained in the inner nuclear membrane, whereas the transmembrane segments with the C-terminal domain of MAN1 is not targeted to the inner nuclear membrane. The N-terminal domain of MAN1 is also sufficient for inner nuclear membrane targeting as it can target a chimeric type II integral protein to this subcellular location. Deletion mutants of the N-terminal of MAN1 are not efficiently retained in the inner nuclear membrane. When the N-terminal domain of MAN1 is increased in size from∼50 kDa to ∼100 kDa, the protein cannot reach the inner nuclear membrane. Fluorescence recovery after photobleaching experiments of MAN1 fused to green fluorescent protein show that the fusion protein is relatively immobile in the nuclear envelope compared with the endoplasmic reticulum of interphase cells, suggesting binding to a nuclear component. These results are in agreement with the `diffusion-retention' model for targeting integral proteins to the inner nuclear membrane.

Autosomal dominant dilated cardiomyopathy with atrioventricular block: a lamin A/C defect-related disease

OBJECTIVES

We investigated the prevalence of lamin A/C (LMNA) gene defects in familial and sporadic dilated cardiomyopathies (DCM) associated with atrioventricular block (AVB) or increased serum creatine-phosphokinase (sCPK), and the corresponding changes in myocardial and protein expression.

BACKGROUND

It has been reported that familial DCM, associated with conduction disturbances or variable myopathies, is causally linked to LMNA gene defects.

METHODS

The LMNA gene and myocardial ultrastructural and immunochemical changes were analyzed in 73 cases of DCM (49 pure, 15 with AVB [seven familial, eight sporadic], 9 with increased sCPK), four cases of familial AVB and 19 non-DCM heart diseases. The normal controls included eight heart donor biopsies for tissue studies and 107 subjects for LMNA gene studies.

RESULTS

Five novel LMNA mutations (K97E, E111X, R190W, E317K, four base pair insertion at 1,713 cDNA) were identified in five cases of familial autosomal dominant DCM with AVB (5/15: 33%). The LMNA expression of the myocyte nuclei was reduced or absent. Western blot protein analyses of three hearts with different mutations showed an additional 30-kDa band, suggesting a degrading effect of mutated on wild-type protein. Focal disruptions, bleb formation and nuclear pore clustering were documented by electron microscopy of the myocyte nuclear membranes. None of these changes and no mutations were found in the nine patients with DCM and increased sCPK or in the disease and normal controls.

CONCLUSIONS

The LMNA gene mutations account for 33% of the DCMs with AVB, all familial autosomal dominant. Increased sCPK in patients with DCM without AVB is not a useful predictor of LMNA mutation.

Characterization of adiposity and metabolism in Lmna-deficient mice

Dunnigan's Familial Partial Lipodystrophy (FPLD) is an autosomal dominant disease characterized by regional fat loss and insulin resistance. FPLD is caused by mutations in the LMNA gene, which encodes intermediate filaments of the nuclear lamina. Different LMNA mutations cause Emery-Dreifuss muscular dystrophy and/or a dilated cardiomyopathy. It is not known how LMNA mutations cause any of the disease phenotypes. Here we measure physical and metabolic characteristics of Lmna-/- and +/- mice to determine their usefulness as models for FPLD. Lmna-/- mice, which die prematurely of muscular dystrophy, have little fat, but do not show the insulin resistance characteristic of FPLD. Lmna+/- mice, despite treatment with a high fat diet, do not have decreased fat stores or metabolic features of FPLD. We also show, in mice, that Lmna transcripts are expressed at high levels in muscle and adipose tissue, but do not vary by body region or sex. In conclusion, Lmna+/- and -/- mice do not mimic Dunnigan's FPLD, and differential expression of lamins A and C does not appear to contribute to sex- or tissue-specific LMNA phenotypes.

Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is characterised by early contractures, slowly progressive muscle wasting and weakness with a distinctive humero-peroneal distribution and cardiac conduction defects leading to dilated cardiomyopathy. The genes known to be responsible for EDMD encode proteins associated with the nuclear envelope: the emerin and the lamins A and C.

Homozygous defects in LMNA, encoding lamin A/C nuclear-envelope proteins, cause autosomal recessive axonal neuropathy in human (Charcot-Marie-Tooth disorder type 2) and mouse

The Charcot-Marie-Tooth (CMT) disorders comprise a group of clinically and genetically heterogeneous hereditary motor and sensory neuropathies, which are mainly characterized by muscle weakness and wasting, foot deformities, and electrophysiological, as well as histological, changes. A subtype, CMT2, is defined by a slight or absent reduction of nerve-conduction velocities together with the loss of large myelinated fibers and axonal degeneration. CMT2 phenotypes are also characterized by a large genetic heterogeneity, although only two genes---NF-L and KIF1Bbeta---have been identified to date. Homozygosity mapping in inbred Algerian families with autosomal recessive CMT2 (AR-CMT2) provided evidence of linkage to chromosome 1q21.2-q21.3 in two families (Zmax=4.14). All patients shared a common homozygous ancestral haplotype that was suggestive of a founder mutation as the cause of the phenotype. A unique homozygous mutation in LMNA (which encodes lamin A/C, a component of the nuclear envelope) was identified in all affected members and in additional patients with CMT2 from a third, unrelated family. Ultrastructural exploration of sciatic nerves of LMNA null (i.e., -/-) mice was performed and revealed a strong reduction of axon density, axonal enlargement, and the presence of nonmyelinated axons, all of which were highly similar to the phenotypes of human peripheral axonopathies. The finding of site-specific amino acid substitutions in limb-girdle muscular dystrophy type 1B, autosomal dominant Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy type 1A, autosomal dominant partial lipodystrophy, and, now, AR-CMT2 suggests the existence of distinct functional domains in lamin A/C that are essential for the maintenance and integrity of different cell lineages. To our knowledge, this report constitutes the first evidence of the recessive inheritance of a mutation that causes CMT2; additionally, we suggest that mutations in LMNA may also be the cause of the genetically overlapping disorder CMT2B1.

The muscular dystrophies

The muscular dystrophies are inherited myogenic disorders characterised by progressive muscle wasting and weakness of variable distribution and severity. They can be subdivided into several groups, including congenital forms, in accordance with the distribution of predominant muscle weakness: Duchenne and Becker; Emery-Dreifuss; distal; facioscapulohumeral; oculopharyngeal; and limb-girdle which is the most heterogeneous group. In several dystrophies the heart can be seriously affected, sometimes in the absence of clinically significant weakness. The genes and their protein products that cause most of these disorders have now been identified. This information is essential to establish an accurate diagnosis and for reliable genetic counselling and prenatal diagnosis. There is, as yet, no way of greatly affecting the long-term course of any of these diseases. However, advances in gene manipulation and stem-cell therapy suggest cautious optimism for finding an effective treatment in the not-too-distant future.

Homozygous defects in LMNA, encoding lamin A/C nuclear-envelope proteins, cause autosomal recessive axonal neuropathy in human (Charcot-Marie-Tooth disorder type 2) and mouse

The Charcot-Marie-Tooth (CMT) disorders comprise a group of clinically and genetically heterogeneous hereditary motor and sensory neuropathies, which are mainly characterized by muscle weakness and wasting, foot deformities, and electrophysiological, as well as histological, changes. A subtype, CMT2, is defined by a slight or absent reduction of nerve-conduction velocities together with the loss of large myelinated fibers and axonal degeneration. CMT2 phenotypes are also characterized by a large genetic heterogeneity, although only two genes---NF-L and KIF1Bbeta---have been identified to date. Homozygosity mapping in inbred Algerian families with autosomal recessive CMT2 (AR-CMT2) provided evidence of linkage to chromosome 1q21.2-q21.3 in two families (Zmax=4.14). All patients shared a common homozygous ancestral haplotype that was suggestive of a founder mutation as the cause of the phenotype. A unique homozygous mutation in LMNA (which encodes lamin A/C, a component of the nuclear envelope) was identified in all affected members and in additional patients with CMT2 from a third, unrelated family. Ultrastructural exploration of sciatic nerves of LMNA null (i.e., -/-) mice was performed and revealed a strong reduction of axon density, axonal enlargement, and the presence of nonmyelinated axons, all of which were highly similar to the phenotypes of human peripheral axonopathies. The finding of site-specific amino acid substitutions in limb-girdle muscular dystrophy type 1B, autosomal dominant Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy type 1A, autosomal dominant partial lipodystrophy, and, now, AR-CMT2 suggests the existence of distinct functional domains in lamin A/C that are essential for the maintenance and integrity of different cell lineages. To our knowledge, this report constitutes the first evidence of the recessive inheritance of a mutation that causes CMT2; additionally, we suggest that mutations in LMNA may also be the cause of the genetically overlapping disorder CMT2B1.

Molecular Mechanisms of Inherited Cardiomyopathies

Cardiomyopathies are diseases of heart muscle that may result from a diverse array of conditions that damage the heart and other organs and impair myocardial function, including infection, ischemia, and toxins. However, they may also occur as primary diseases restricted to striated muscle. Over the past decade, the importance of inherited gene defects in the pathogenesis of primary cardiomyopathies has been recognized, with mutations in some 18 genes having been identified as causing hypertrophic cardiomyopathy (HCM) and/or dilated cardiomyopathy (DCM). Defining the role of these genes in cardiac function and the mechanisms by which mutations in these genes lead to hypertrophy, dilation, and contractile failure are major goals of ongoing research. Pathophysiological mechanisms that have been implicated in HCM and DCM include the following: defective force generation, due to mutations in sarcomeric protein genes; defective force transmission, due to mutations in cytoskeletal protein genes; myocardial energy deficits, due to mutations in ATP regulatory protein genes; and abnormal Ca2+ homeostasis, due to altered availability of Ca2+ and altered myofibrillar Ca2+ sensitivity. Improved understanding that will result from these studies should ultimately lead to new approaches for the diagnosis, prognostic stratification, and treatment of patients with heart failure.

Myne-1, a spectrin repeat transmembrane protein of the myocyte inner nuclear membrane, interacts with lamin A/C

Mutations in the genes encoding the inner nuclear membrane proteins lamin A/C and emerin produce cardiomyopathy and muscular dystrophy in humans and mice. The mechanism by which these broadly expressed gene products result in tissue-specific dysfunction is not known. We have identified a protein of the inner nuclear membrane that is highly expressed in striated and smooth muscle. This protein, myne-1 (myocyte nuclear envelope), is predicted to have seven spectrin repeats, an interrupted LEM domain and a single transmembrane domain at its C-terminus. We found that myne-1 is expressed upon early muscle differentiation in multiple intranuclear foci concomitant with lamin A/C expression. In mature muscle, myne-1 and lamin A/C are perfectly colocalized, although colocalization with emerin is only partial. Moreover, we show that myne-1 and lamin A/C coimmunoprecipitate from differentiated muscle in vitro. The muscle-specific inner nuclear envelope expression of myne-1, along with its interaction with lamin A/C, indicates that this gene is a potential mediator of cardiomyopathy and muscular dystrophy.

Autosomal dominant Emery-Dreifuss muscular dystrophy: a new family with late diagnosis

Emery-Dreifuss muscular dystrophy is characterized by the clinical triad of early onset contractures of elbows, Achilles tendons and spine, wasting and weakness with a predominantly humero-peroneal distribution and life-threatening cardiac conduction defects and/or cardiomyopathy. Two main types of inheritance have been described: the X-linked form is caused by mutations in the STA gene on locus Xq28 and the gene for the autosomal dominant form (LMNA gene) has been localized on chromosome 1q11-q23. Recently, mutations in this LMNA gene have been also found to be responsible for the less frequent autosomal recessive form of the disease. Although all forms share a similar clinical presentation, some differences appear to exist between them as has been described recently in a large number of patients. We present the first documented Spanish family genetically confirmed to have autosomal dominant Emery-Dreifuss muscular dystrophy. Clinical, pathological and genetic data are described. We emphasize the difficulties in diagnosis, especially in sporadic cases or young patients in whom the clinical picture is not completely established.

BAF is required for emerin assembly into the reforming nuclear envelope

Mutations in emerin cause the X-linked recessive form of Emery-Dreifuss muscular dystrophy (EDMD). Emerin localizes at the inner membrane of the nuclear envelope (NE) during interphase, and diffuses into the ER when the NE disassembles during mitosis. We analyzed the recruitment of wildtype and mutant GFP-tagged emerin proteins during nuclear envelope assembly in living HeLa cells. During telophase, emerin accumulates briefly at the ‘core’ region of telophase chromosomes, and later distributes over the entire nuclear rim. Barrier-to-autointegration factor (BAF), a protein that binds nonspecifically to double-stranded DNA in vitro, co-localized with emerin at the ‘core’ region of chromosomes during telophase. An emerin mutant defective for binding to BAF in vitro failed to localize at the ‘core’ in vivo, and subsequently failed to localize at the reformed NE. In HeLa cells that expressed BAF mutant G25E, which did not show ‘core’ localization, the endogenous emerin proteins failed to localize at the ‘core’ region during telophase, and did not assemble into the NE during the subsequent interphase. BAF mutant G25E also dominantly dislocalized LAP2β and lamin A from the NE, but had no effect on the localization of lamin B. We conclude that BAF is required for the assembly of emerin and A-type lamins at the reforming NE during telophase, and may mediate their stability in the subsequent interphase.

Nuclear envelope disorganization in fibroblasts from lipodystrophic patients with heterozygous R482Q/W mutations in the lamin A/C gene

Dunnigan-type familial partial lipodystrophy (FPLD), characterized by an abnormal body fat redistribution with insulin resistance, is caused by missense heterozygous mutations in A-type lamins (lamins A and C). A- and B-type lamins are ubiquitous intermediate filament proteins that polymerize at the inner face of the nuclear envelope. We have analyzed primary cultures of skin fibroblasts from three patients harboring R482Q or R482W mutations. These cells were euploid and able to cycle and divide. A subpopulation of these cells had abnormal blebbing nuclei with A-type lamins forming a peripheral meshwork, which was frequently disorganized. Inner nuclear membrane protein emerin, an A-type lamin-binding protein, strictly colocalized with this abnormal meshwork. Cells from lipodystrophic patients often had other nuclear envelope defects, mainly consisting of nuclear envelope herniations that were deficient in B-type lamins, nuclear pore complexes, lamina-associated protein 2 beta, and chromatin. The mechanical properties of nuclear envelopes were altered, as judged from the extensive deformations observed in nuclei from heat-shocked cells, and from the low stringency of extraction of their components. These structural nuclear alterations were caused by the lamins A/C mutations, as the same changes were introduced in human control fibroblasts by ectopic expression of R482W mutated lamin A.

Nuclear envelope defects associated withLMNAmutations cause dilated cardiomyopathy and Emery-Dreifuss muscular dystrophy

Nuclear lamin A and C alleles that are linked to three distinct human diseases have been expressed both in HeLa cells and in fibroblasts derived from Lmna null mice. Point mutations that cause dilated cardiomyopathy (L85R and N195K) and autosomal dominant Emery-Dreifuss muscular dystrophy (L530P) modify the assembly properties of lamins A and C and cause partial mislocalization of emerin, an inner nuclear membrane protein, in HeLa cells. At the same time, these mutant lamins interfere with the targeting and assembly of endogenous lamins and in this way may cause significant changes in the molecular organization of the nuclear periphery. By contrast, lamin A and C molecules harboring a point mutation (R482W), which gives rise to a dominant form of familial partial lipodystrophy, behave in a manner that is indistinguishable from wild-type lamins A and C, at least with respect to targeting and assembly within the nuclear lamina. Taken together, these results suggest that nuclear structural defects could contribute to the etiology of both dilated cardiomyopathy and autosomal dominant Emery-Dreifuss muscular dystrophy.

Properties of lamin A mutants found in Emery-Dreifuss muscular dystrophy, cardiomyopathy and Dunnigan-type partial lipodystrophy

Autosomal dominant Emery-Dreifuss muscular dystrophy is caused by mutations in the LMNA gene, which encodes lamin A and lamin C. Mutations in this gene also give rise to limb girdle muscular dystrophy type 1B, dilated cardiomyopathy with atrioventricular conduction defect and Dunnigan-type partial lipodystrophy. The properties of the mutant lamins that cause muscular dystrophy, lipodystrophy and dilated cardiomyopathy are not known. We transfected C2C12 myoblasts with cDNA encoding wild-type lamin A and 15 mutant forms found in patients affected by these diseases. Immunofluorescence microscopy showed that four mutants, N195K, E358K, M371K and R386K, could have a dramatically aberrant localization, with decreased nuclear rim staining and formation of intranuclear foci. The distributions of endogenous lamin A/C, lamin B1 and lamin B2 were also altered in cells expressing these four mutants and three of them caused a loss of emerin from the nuclear envelope. In the yeast two-hybrid assay, the 15 lamin A mutants studied interacted with themselves and with wild-type lamin A and lamin B1. Pulse-chase experiments showed no decrease in the stability of several representative lamin A mutants compared with wild-type. These results indicate that some lamin A mutants causing disease can be aberrantly localized, partially disrupt the endogenous lamina and alter emerin localization, whereas others localize normally in transfected cells.

Distinct changes in intranuclear lamin A/C organization during myoblast differentiation

Intranuclear lamin foci or speckles have been observed in various cell types. In order to explore the possibility of changes in internal lamin organization during muscle differentiation, we have examined the appearance of A-type lamin speckles that associate with RNA splicing factor speckles in C2C12 myoblasts and myotubes. Lamin speckles were observed in dividing myoblasts but disappeared early during the course of differentiation in postmitotic myocytes, and were absent in myotubes and muscle fibers. However, no changes were seen in the typical peripheral organization of lamins A/C or B1 or in RNA splicing factor speckles. Lamin speckles were also absent in quiescent myoblasts but reappeared as cells were reactivated to enter the cell cycle. These changes were not observed in other quiescent cell types. Immunoblot analysis indicated that the abundance and migration of lamins A and C was not altered in differentiated myoblasts. When myotube or quiescent myoblast nuclei were extracted with nucleases and detergent, a uniformly stained internal lamina was revealed, indicating that lamins A/C were antigenically masked in these cells, probably owing to structural reorganization of the lamina during differentiation or quiescence. Our results suggest that muscle cell differentiation is accompanied by regulated rearrangements in the organization of the A-type lamins.

The nuclear envelope in muscular dystrophy and cardiovascular diseases

Considerable interest has been focused on the nuclear envelope in recent years following the realization that several human diseases are linked to defects in genes encoding nuclear envelope specific proteins, most notably A-type lamins and emerin. These disorders, described as laminopathies or nuclear envelopathies, include both X-linked and autosomal dominant forms of Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy with conduction system defects, limb girdle muscular dystrophy 1B with atrioventricular conduction disturbances, and Dunnigan-type familial partial lipodystrophy. Certain of these diseases are associated with nuclear structural abnormalities that can be seen in a variety of cells and tissues. These observations clearly demonstrate that A-type lamins in particular play a central role, not only in the maintenance of nuclear envelope integrity but also in the large-scale organization of nuclear architecture. What is not obvious, however, is why defects in nuclear envelope proteins that are found in most adult cell types should give rise to pathologies associated predominantly with skeletal and cardiac muscle and adipocytes. The recognition of these various disorders now raises the novel possibility that the nuclear envelope may have functions that go beyond housekeeping and which impact upon cell-type specific nuclear processes.

Nuclear envelope dynamics

The nuclear envelope (NE) provides a semi permeable barrier between the nucleus and cytoplasm and plays a central role in the regulation of macromolecular trafficking between these two compartments. In addition to this transport function, the NE is a key determinant of interphase nuclear architecture. Defects in NE proteins such as A-type lamins and the inner nuclear membrane protein, emerin, result in several human diseases that include cardiac and skeletal myopathies as well as lipodystrophy. Certain disease-linked A-type lamin defects cause profound changes in nuclear organization such as loss of peripheral heterochromatin and redistribution of other nuclear envelope components. While clearly essential in maintenance of nuclear integrity, the NE is a highly dynamic organelle. In interphase it is constantly remodeled to accommodate nuclear growth. During mitosis it must be completely dispersed so that the condensed chromosomes may gain access to the mitotic spindle. Upon completion of mitosis, dispersed NE components are reutilized in the assembly of nuclei within each daughter cell. These complex NE rearrangements are under precise temporal and spatial control and involve interactions with microtubules, chromatin, and a variety of cell-cycle regulatory molecules.Key words: nuclear envelope, lamin, nuclear pore complex, nuclear membranes, mitosis.

Nuclear membrane protein LAP2β mediates transcriptional repression alone and together with its binding partner GCL (germ-cell-less)

LAP2β is an integral membrane protein of the nuclear envelope involved in chromatin and nuclear architecture. Using the yeast two-hybrid system, we have cloned a novel LAP2β-binding protein, mGCL, which contains a BTB/POZ domain and is the mouse homologue of the Drosophila germ-cell-less (GCL) protein. In Drosophila embryos, GCL was shown to be essential for germ cell formation and was localized to the nuclear envelope. Here, we show that, in mammalian cells, GCL is co-localized with LAP2β to the nuclear envelope. Nuclear fractionation studies reveal that mGCL acts as a nuclear matrix component and not as an integral protein of the nuclear envelope. Recently, mGCL was found to interact with the DP3α component of the E2F transcription factor. This interaction reduced the transcriptional activity of the E2F-DP heterodimer, probably by anchoring the complex to the nuclear envelope. We demonstrate here that LAP2β is also capable of reducing the transcriptional activity of the E2F-DP complex and that it is more potent than mGCL in doing so. Co-expression of both LAP2β and mGCL with the E2F-DP complex resulted in a reduced transcriptional activity equal to that exerted by the pRb protein.

Novel and recurrent mutations in lamin A/C in patients with Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is characterized by slowly progressive muscle wasting and weakness; early contractures of the elbows, Achilles tendons, and spine; and cardiomyopathy associated with cardiac conduction defects. Clinically indistinguishable X-linked and autosomal forms of EDMD have been described. Mutations in the STA gene, encoding the nuclear envelope protein emerin, are responsible for X-linked EDMD, while mutations in the LMNA gene encoding lamins A and C by alternative splicing have been found in patients with autosomal dominant, autosomal recessive, and sporadic forms of EDMD. We report mutations in LMNA found in four familial and seven sporadic cases of EDMD, including seven novel mutations. Nine missense mutations and two small in-frame deletions were detected distributed throughout the gene. Most mutations (7/11) were detected within the LMNA exons encoding the central rod domain common to both lamins A/C. All of these missense mutations alter residues in the lamin A/C proteins conserved throughout evolution, implying an essential structural and/or functional role of these residues. One severely affected patient possesed two mutations, one specific to lamin A that may modify the phenotype of this patient. Mutations in LMNA were frequently identified among patients with sporadic and familial forms of EDMD. Further studies are needed to identify the factors modifying disease phenotype among patients harboring mutations within lamin A/C and to determine the effect of various mutations on lamin A/C structure and function.

The genetics of type 2 diabetes

Type 2 diabetes mellitus is not a single disease but a genetically heterogeneous group of metabolic disorders sharing glucose intolerance. The precise underlying biochemical defects are unknown and almost certainly include impairments of both insulin secretion and action. The rapidly increasing prevalence of T2D world wide makes it a major cause of morbidity and mortality. Understanding the genetic aetiology of T2D will facilitate its diagnosis, treatment and prevention. The results of linkage and association studies to date demonstrate that, as with other common diseases, multiple genes are involved in the susceptibility to T2D, each making a modest contribution to the overall risk. The completion of the draft human genome sequence and a brace of novel tools for genomic analysis promise to accelerate progress towards a more complete molecular description of T2D.

Novel lamin A/C mutations in two families with dilated cardiomyopathy and conduction system disease

BACKGROUND

The LMNA gene, one of 6 autosomal disease genes implicated in familial dilated cardiomyopathy, encodes lamins A and C, alternatively spliced nuclear envelope proteins. Mutations in lamin A/C cause 4 diseases: Emery-Dreifuss muscular dystrophy, limb girdle muscular dystrophy type 1B, Dunnigan-type familial partial lipodystrophy, and dilated cardiomyopathy.

METHODS AND RESULTS

Two 4-generation white families with autosomal dominant familial dilated cardiomyopathy and conduction system disease were found to have novel mutations in the rod segment of lamin A/C. In family A a missense mutation (nucleotide G607A, amino acid E203K) was identified in 14 adult subjects; disease was manifest as progressive conduction disease in the fourth and fifth decades. Death was caused by heart failure. In family B a nonsense mutation (nucleotide C673T, amino acid R225X) was identified in 10 adult subjects; disease was also manifest as progressive conduction disease but with earlier onset (third and fourth decades), ventricular dysrhythmias, left ventricular enlargement, and systolic dysfunction. Death was caused by heart failure and sudden cardiac death. Skeletal muscle disease was not observed in either family.

CONCLUSIONS

Novel rod segment mutations in lamin A/C cause variable conduction system disease and dilated cardiomyopathy without skeletal myopathy.

A missense mutation in the exon 8 of lamin A/C gene in a Japanese case of autosomal dominant limb-girdle muscular dystrophy and cardiac conduction block

A case of autosomal dominant limb-girdle muscular dystrophy with atrioventricular conduction block (LGMD1B) has been documented. In this family, 13 members, nine males and four females, had cardiac arrhythmia requiring pacemakers. The proband, a 67-year-old male, had longstanding proximal muscle weakness later associated with cardiac arrhythmia but showed neither rigid spine nor joint contracture. His muscle enzymes were within normal range and muscle biopsy showed myopathic changes. Gene analysis of the proband revealed Tyr481His mutation in the exon 8 of lamin A/C (LMNA) gene which is adjacent to the codon mutated in reported cases of familial partial lipodystrophy. This is the first report of muscular dystrophy shown to have a mutation of LMNA in a Japanese family as well as the first case of missense mutation in the exon 8 with LGMD1B phenotype.

Skeletal muscle pathology in autosomal dominant Emery-Dreifuss muscular dystrophy with lamin A/C mutations

We present our observations on the skeletal muscle pathology of nine cases from seven families of autosomal dominant Emery-Dreifuss muscular dystrophy (ADEDMD) with identified mutations in the lamin A/C gene, aged 2-35 years at the time of biopsy. The severity of pathological change was moderate and the most common features were variation in fibre size (hypertrophy and atrophy), an increase in internal nuclei and smaller diameter fibres with high oxidative enzyme activity. Only one case showed necrosis, which was present in two separate samples taken from the quadriceps and tibialis anterior, at different ages. Immunocytochemistry detected an age-related reduction of laminin beta1 on the muscle fibres in adolescent and adult cases. Antibodies to lamins A and A/C, and emerin did not reveal any detectable differences from controls. Electron microscopy of two out of three cases showed an abnormal distribution of heterochromatin in many fibre nuclei. Our results show that dystrophic changes in skeletal muscle are not a major feature of ADEDMD, and that nuclear abnormalities may be detected with electron microscopy. Immunodetection of reduced laminin beta1 may be a useful secondary marker in adults with this disorder, as immunocytochemistry of lamins is not yet of diagnostic use.

Adipose tissue and the insulin resistance syndrome

Obesity is associated with insulin resistance. Insulin resistance underlies a constellation of adverse metabolic and physiological changes (the insulin resistance syndrome) which is a strong risk factor for development of type 2 diabetes and CHD. The present article discusses how accumulation of triacylglycerol in adipocytes can lead to deterioration of the responsiveness of glucose metabolism in other tissues. Lipodystrophy, lack of adipose tissue, is also associated with insulin resistance. Any plausible explanation for the link between excess adipose tissue and insulin resistance needs to be able to account for this observation. Adipose tissue in obesity becomes refractory to suppression of fat mobilization by insulin, and also to the normal acute stimulatory effect of insulin on activation of lipoprotein lipase (involved in fat storage). The net effect is as though adipocytes are 'full up' and resisting further fat storage. Thus, in the postprandial period especially, there is an excess flux of circulating lipid metabolites that would normally have been 'absorbed' by adipose tissue. This situation leads to fat deposition in other tissues. Accumulation of triacylglycerol in skeletal muscles and in liver is associated with insulin resistance. In lipodystrophy there is insufficient adipose tissue to absorb the postprandial influx of fatty acids, so these fatty acids will again be directed to other tissues. This view of the link between adipose tissue and insulin resistance emphasises the important role of adipose tissue in 'buffering' the daily influx of dietary fat entering the circulation and preventing excessive exposure of other tissues to this influx.

Please pass the chips: genomic insights into obesity and diabetes

Type 2 diabetes mellitus is an increasingly common disorder of carbohydrate and lipid metabolism. Approximately 16 million individuals in the United States have diabetes, and 800,000 new cases are identified each year. Two important characteristics of this disease are insulin resistance, the failure of peripheral tissues, including liver, muscle, and adipose tissue, to respond to physiologic doses of insulin, and failure of pancreatic beta-cells to properly secrete insulin in response to elevated blood glucose levels. Obesity is a significant risk factor for the development of type 2 diabetes mellitus. Recent observations of extremely lean, lipoatrophic models have revealed a similar predisposition to developing diabetes. Although it may seem paradoxical that both increased adiposity and severely reduced fat mass cause diabetes, a common pathophysiologic process in fat may be responsible for the predisposition to develop hyperglycemia in both conditions. This review will focus on the important role of adipose tissue dysfunction in the pathogenesis of diabetes, and on insights gained through the application of microarray technology to analyze adipocyte gene expression.

Fine mapping of the PSORS4 psoriasis susceptibility region on chromosome 1q21

Psoriasis is a chronic skin disorder affecting approximately 2% of the Caucasian population. Family clustering of the disease is well established and nonparametric linkage analyzes have mapped disease susceptibility loci on chromosomes 6p (PSORS1) and 17q (PSORS2). Nonconfirmed evidence for linkage is also available for chromosomes 2q 3q, 4q (PSORS3), 8q, 16q, and 20p. We mapped an additional susceptibility locus on chromosome 1q21 (PSORS4). In this study, we have carried out a linkage disequilibrium analysis, in order to achieve a finer localization. We recruited 79 triads from continental Italy and typed them at five loci spanning the 1.6 Mb region generating the highest multipoint LOD scores in our previous linkage study. We observed significant evidence for association with D1S2346 marker (p = 0.004). Results consistent with this data were obtained by typing an independent sample that included 28 patients and 56 controls, originating from Sardinia. In fact, p values of 0.02 were observed with both D1S2346 and D1S2715 markers. We sought further confirmation of our results by typing both samples with two novel markers (140J1C and 140J1D) flanking D1S2346. Marker 140J1D generated a p value of 0.003 in the continental Italy sample where a D1S2346/140J1D haplotype was found with a higher frequency among patients' chromosomes. Altogether our data indicate that the 1q21 susceptibility gene may be localized in the genomic interval spanned by D1S2346 and 140J1D. This report provides evidence supporting the refinement of a non-HLA psoriasis susceptibility locus.

Both emerin and lamin C depend on lamin A for localization at the nuclear envelope

Physical interactions between lamins and emerin were investigated by co-immunoprecipitation of in vitro translated proteins. Emerin interacted with in vitro translated lamins A, B1 and C in co-immunprecipitation reactions. Competition reactions revealed a clear preference for interactions between emerin and lamin C. Structural associations between lamins and emerin were investigated in four human cell lines displaying abnormal expression and/or localisation of lamins A and C. In each cell line absence of lamins A and C from the nuclear envelope (NE) was correlated with mis-localisation of endogenous and exogenous emerin to the ER. In two cell lines that did not express lamin A but did express lamin C, lamin C as well as emerin was mis-localised. When GFP-lamin A was expressed in SW13 cells (which normally express only very low levels of endogenous lamin A and mis-localise endogenous emerin and lamin C), all three proteins became associated with the NE. When GFP-lamin C was expressed in SW13 cells neither the endogenous nor the exogenous lamin C was localised to the NE and emerin remained in the ER. Finally, lamins A and C were selectively eliminated from the NE of HeLa cells using a dominant negative mutant of lamin B1. Elimination of these lamins from the lamina led to the accumulation of emerin as aggregates within the ER. Our data suggest that lamin A is essential for anchorage of emerin to the inner nuclear membrane and of lamin C to the lamina.

SP3 and AP-1 mediate transcriptional activation of the lamin A proximal promoter

Lamin A is a major component of the nuclear lamina that is expressed in various types of differentiated cells. We have analysed previously the putative promoter sequences of the gene and shown that the rat lamin A proximal promoter contains two essential motifs, a GC box that can bind to Sp1 and Sp3, and an AP-1 motif that can bind to c-Jun and c-Fos. In this study we have investigated the role of Sp1 and Sp3 in transactivation of the promoter. Functional analysis of the promoter in Drosophila SL2 cells has demonstrated that it is inactive in the absence of Sp proteins. Activation by expression of Sp3 is more pronounced than that by Sp1 although both proteins can bind to the GC box in vitro; activation clearly depends on an intact GC box as deduced from mutant analysis. Promoter activity in SL2 cells also requires an intact AP-1 motif, which can bind to endogenous Drosophila Jun and Fos proteins. Furthermore, overexpression of c-Jun and c-Fos results in fourfold activation of the promoter in PCC-4 embryonal carcinoma cells. Our demonstration that activation of the lamin A proximal promoter is mediated by Sp3 and AP-1 transcription factors affords a basis for further studies on the regulation of this important gene during development and disease.

Transgenic overexpression of leptin rescues insulin resistance and diabetes in a mouse model of lipoatrophic diabetes

Lipoatrophic diabetes is caused by a deficiency of adipose tissue and is characterized by severe insulin resistance, hypoleptinemia, and hyperphagia. The A-ZIP/F-1 mouse (A-ZIPTg/+) is a model of severe lipoatrophic diabetes and is insulin resistant, hypoleptinemic, hyperphagic, and shows severe hepatic steatosis. We have also produced transgenic "skinny" mice that have hepatic overexpression of leptin (LepTg/+) and no adipocyte triglyceride stores, and are hypophagic and show increased insulin sensitivity. To explore the pathophysiological and therapeutic roles of leptin in lipoatrophic diabetes, we crossed LepTg/+ and A-ZIPTg/+ mice, producing doubly transgenic mice (LepTg/+:A-ZIPTg/+) virtually lacking adipose tissue but having greatly elevated leptin levels. The LepTg/+:A-ZIPTg/+ mice were hypophagic and showed improved hepatic steatosis. Glucose and insulin tolerance tests revealed increased insulin sensitivity, comparable to LepTg/+ mice. These effects were stable over at least 6 months of age. Pair-feeding the A-ZIPTg/+ mice to the amount of food consumed by LepTg/+:A-ZIPTg/+ mice did not improve their insulin resistance, diabetes, or hepatic steatosis, demonstrating that the beneficial effects of leptin were not due to the decreased food intake. Continuous leptin administration that elevates plasma leptin concentrations to those of LepTg/+:A-ZIPTg/+ mice also effectively improved hepatic steatosis and the disorder of glucose and lipid metabolism in A-ZIP/F-1 mice. These data demonstrate that leptin can improve the insulin resistance and diabetes of a mouse model of severe lipoatrophic diabetes, suggesting that leptin may be therapeutically useful in the long-term treatment of lipoatrophic diabetes.

Keratin 8 mutations in patients with cryptogenic liver disease

BACKGROUND

About 10 percent of patients who undergo liver transplantation have cryptogenic liver disease. In animal models, the absence of heteropolymeric keratins 8 and 18 or the presence of mutant keratins in hepatocytes causes or promotes liver disease. We have previously described a mutation in the keratin 18 gene in a patient with cryptogenic cirrhosis, but the importance of mutations in the keratin 8 and keratin 18 genes in such patients is unclear.

METHODS

We tested for mutations in the keratin 8 and keratin 18 genes in purified genomic DNA isolated from 150 explanted livers and 89 peripheral-blood specimens from three groups of patients: 55 patients with cryptogenic liver disease; 98 patients with noncryptogenic liver disease, with causes that included alcohol use, autoimmunity, drug use, and viral infections; and 86 randomly selected inpatients and outpatients who provided blood to the hematology laboratory.

RESULTS

Of the 55 patients with cryptogenic liver disease, 3 had glycine-to-cysteine mutations at position 61 (a highly conserved glycine) of keratin 8, and 2 had tyrosine-to-histidine mutations at position 53 of keratin 8. These mutations were not detected in the patients with other liver diseases or in the randomly selected patients. We verified the presence of the mutations in specimens of explanted livers by protein analysis and by the detection of unique restriction-enzyme cleavage sites. In transfected cells, the glycine-to-cysteine mutation limited keratin-filament reorganization when the cells were exposed to oxidative stress. In contrast, the tyrosine-to-histidine mutation destabilized keratin filaments when transfected cells were exposed to heat or okadaic acid stress.

CONCLUSIONS

Mutations in the keratin 8 gene may predispose people to liver disease and may account for cryptogenic liver disease in some patients.

Premature atherosclerosis associated with monogenic insulin resistance

BACKGROUND

The common insulin resistance syndrome, with obesity, dyslipidemia, hyperglycemia, and hypertension, is associated with increased risk of atherosclerosis. Early atherosclerosis in rare monogenic forms of insulin resistance, however, has not been extensively documented. Cardiovascular end points were thus evaluated in subjects with Dunnigan-type familial partial lipodystrophy (FPLD) due to mutations at LMNA codon 482.

METHODS AND RESULTS

FPLD subjects >/=35 years old were stratified by genotype for either the LMNA R482Q or R482W mutation. Twenty-three subjects were heterozygous mutation carriers, and 17 were R482/R482 homozygous family control subjects. All LMNA mutation carriers had FPLD with insulin resistance. In addition, LMNA mutation carriers had significantly more type 2 diabetes, hypertension, and dyslipidemia than normal family control subjects. Eight LMNA mutation carriers had coronary heart disease (CHD), compared with 1 normal control subject (OR 5.9, 95% CI 1.2 to 30.2). Six LMNA mutation carriers had CHD end points before age 55 years, and 4 of these, all women, had been hospitalized for CABG surgery between the ages of 35 and 54 years.

CONCLUSIONS

Rare LMNA mutations that underlie FPLD with insulin resistance and hyperinsulinemia are also associated with early CHD, notably in women. This suggests that abnormalities of the nuclear envelope can result in a phenotype that recapitulates most of the important attributes of the common insulin resistance syndrome, including accelerated cardiovascular disease. FPLD thus appears to be an appropriate human monogenic model for the common insulin resistance syndrome.

Cardiomyopathy in animal models of muscular dystrophy

Arrhythmia and cardiomyopathy frequently accompany muscular dystrophy. In the last year, the cardiovascular consequences of muscular dystrophy gene mutations have been established through studies of murine models. These models have highlighted the potential role of primary defects in cardiac muscle as well as those secondary cardiovascular outcomes that arise from severe muscle disease. This review focuses on three areas. Recent studies using mouse models have shown that the dystrophin-associated proteins, the sarcoglycans and alpha-dystrobrevin, are critical for both cardiac and skeletal muscle membrane function, yet may exert their roles by different molecular mechanisms. New findings have shown that cytoskeletal proteins at the nuclear membrane, such as emerin and lamin AC, cause muscular dystrophy and cardiomyopathy with cardiac conduction system disease. Finally, the mechanism of cardiac and muscle degeneration in myotonic dystrophy has been re-evaluated through a series of studies using murine models. Implications for human therapy are considered in light of these new findings.

Dyslipemia in familial partial lipodystrophy caused by an R482W mutation in the LMNA gene

Lipatrophic diabetes, also referred to as familial partial lipodystrophy, is a rare disease that is metabolically characterized by hypertriglyceridemia and insulin resistance. Affected patients typically present with regional loss of body fat and muscular hypertrophic appearance. Variable symptoms may comprise pancreatitis and/or eruptive xanthomas due to severe hypertriglyceridemia, acanthosis nigricans, polycystic ovaria, and carpal tunnel syndrome. Mutations within the LMNA gene on chromosome 1q21.2 were recently reported to result in the phenotype of familial partial lipodystrophy. The genetic trait is autosomal dominant. We identified a family with partial lipodystrophy carrying the R482W (Arg(482)Trp) missense mutation within LMNA. Here we present the lipoprotein characteristics in this family in detail. Clinically, the loss of sc fat and muscular hypertrophy especially of the lower extremities started as early as in childhood. Acanthosis and severe hypertriglyceridemia developed later in life, followed by diabetes. The characterization of the lipoprotein subfractions revealed that affected children present with hyperlipidemia. The presence and severity of hyperlipidemia seem to be influenced by age, apolipoprotein E genotype, and the coexistence of diabetes mellitus. In conclusion, dyslipemia is an early and prominent feature in the presented lipodystrophic family carrying the R482W mutation within LMNA.