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PubMed2001

Subcutaneous abdominal adipocyte size, a predictor of type 2 diabetes, is linked to chromosome 1q21--q23 and is associated with a common polymorphism in LMNA in Pima Indians.

Large subcutaneous abdominal adipocyte size (s.c. abd. AS) is associated with insulin resistance and predicts type 2 diabetes in Pima Indians. Because type 2 diabetes is familial, we aimed to determine whether mean s.c. abd. AS is also familial and if so, to identify chromosomal regions linked to this measure. Body composition (hydrodensitometry) and mean s.c. abd. AS (fat biopsy) were measured in 295 Pima Indians (179 with normal, 80 with impaired, and 36 with diabetic glucose tolerance) representing 164 nuclear families. Mean s.c. abd. AS, adjusted for age, sex, and percentage body fat was a familial trait (heritability h(2) = 0.48, P < 0.0001). A genome-wide autosomal scan revealed suggestive evidence for linkage (LOD 1.73) of adjusted mean s.c. abd. AS to chromosome 1q21--q23, a region containing LMNA, the gene encoding for the nuclear envelope proteins lamin A/C. Rare mutations in LMNA were recently shown to underlie familial partial lipodystrophy (FPLD), a syndrome characterized by regional loss of adipose tissue, insulin resistance, and glucose intolerance. A common (allelic frequency 0.43) single nucleotide polymorphism (silent 1908C --> T substitution) in exon 10 of LMNA (GenBank X03444) was associated with reduced age-, sex- and percentage body fat-adjusted mean s.c. abd. AS [0.80 +/- 0.17 (CC), 0.76 +/- 0.15 (CT), 0.73 +/- 0.16 (TT) microg lipid/cell, P < 0.05 for CC vs TT]. These findings indicate that approximately half of the variance in mean s.c. abd. AS can be attributed to familial factors and that genetic variation in LMNA might not only underlie rare cases of FPLD, but may also contribute to variation in adipocyte size in the general population.

Adipocytes↗

PubMed2005

Type A insulin resistance syndrome revealing a novel lamin A mutation.

Particular forms of polycystic ovary syndrome with severe hyperandrogenism, acanthosis nigricans, and marked insulin resistance, defining the type A insulin resistance syndrome, are due to insulin receptor gene mutations. However, the majority of affected individuals do not have such mutation, arguing for the genetic heterogeneity of this syndrome. The familial partial lipodystrophy of the Dunnigan type, one of the diseases due to mutations in the lamin A/C (LMNA) gene, is characterized by a lipodystrophic phenotype and shares some clinical and metabolic features with the type A syndrome. We describe here the case of a nonobese 24-year-old woman affected with type A syndrome without clinical lipodystrophy. We linked this phenotype to a novel heterozygous missense mutation in the LMNA, predicting a G602S amino acid substitution in lamin A. This mutation cosegregated with impaired glucose tolerance, insulin resistance, and acanthosis nigricans in the absence of clinical lipodystrophy in the family. The skin fibroblasts from the proband exhibited nuclear alterations similar to those described in other laminopathies, and showed several defects in the insulin transduction pathway. This study further extends the vast range of diseases linked to LMNA mutations and identifies another genetic cause for the type A insulin resistance syndrome.

Adult↗

PubMed2003

The phenotypic manifestations of autosomal recessive axonal Charcot-Marie-Tooth due to a mutation in Lamin A/C gene.

Charcot-Marie-Tooth disease constitutes a genetically heterogeneous group of hereditary motor and sensory peripheral neuropathies. The axonal type of Charcot-Marie-Tooth is designated type 2. Six loci for autosomal dominant and three for recessive Charcot-Marie-Tooth type 2 have been reported so far. In this study we report the phenotype of autosomal recessive axonal Charcot-Marie-Tooth type 2 due to a recently-described mutation (c.892C>T-p.R298C) in a gene encoding Lamin A/C nuclear envelope proteins and the first gene in which a mutation leads to autosomal recessive Charcot-Marie-Tooth type 2. We have explored eight patients from four Algerian families. The onset is usually in the second decade and the course is rapid, involving upper limbs and proximal muscles, leading to a severe condition in less than 4 years. Many different mutations in Lamin A/C have been identified as causing variable phenotypes, such as limb girdle muscular dystrophy type 1B, autosomal dominant and recessive Emery-Dreyfuss muscular dystrophy, dilated cardiomyopathy with atrioventricular conduction defect, and Dunnigan-type familial partial lipodystrophy should prompt us to fully investigate the skeletal and cardiac muscles in patients affected with autosomal recessive Charcot-Marie-Tooth type 2 carrying a mutation in LMNA.

Algeria↗

PubMed2004

A lamin A/C beta-strand containing the site of lipodystrophy mutations is a major surface epitope for a new panel of monoclonal antibodies.

Using a phage-displayed peptide library, we have identified the epitope recognized by a new panel of five monoclonal antibodies (mAbs) raised against full-length recombinant human lamin A. The mAbs were found to recognize both lamin A and C by Western blotting and immunolocalization at the nuclear rim. A nine-amino acid consensus sequence PLLTYRFPP in the common immunoglobulin-like (Ig-like) domain of lamin A/C contains the binding site for all five mAbs. Three-dimensional structure of the Ig-like domain of lamin A/C shows this sequence is a complete beta-strand. This sequence includes arginine-482 (R482) which is mutated in most cases of Dunnigan-type familial partial lipodystrophy (FPLD). R482 may be part of an interaction site on the surface of lamin A/C for lamin-binding proteins associated with lipodystrophy.

Amino Acid Sequence↗

PubMed2001

Genetic determinants of type 2 diabetes mellitus.

Type 2 diabetes refers to a group of disparate metabolic diseases, which are typically characterized by insulin resistance in peripheral tissues, together with impaired insulin secretion from pancreatic beta-cells. The complexity of type 2 diabetes is related to factors such as genetic heterogeneity, interactions between genes, and the modulating role played by the environment. Recent progress has included defining the molecular basis of monogenic forms of type 2 diabetes, such as familial partial lipodystrophy and the subtypes of maturity-onset diabetes of the young (MODY), and also the identification of chromosomal regions that may harbor type 2 diabetes susceptibility genes. Many common variants in functional and positional candidate genes, including ADRB3, PPARG, ENPP1, and CAPN10, have also been studied for their possible role as determinants of type 2 diabetes, with varying levels of agreement between studies. The availability of a relatively complete sequence of the human genome will increase the amount of genetic information that can be used to evaluate hypotheses for the genetic basis of type 2 diabetes. To make sense of human type 2 diabetes in the post-genomic era, it is essential to have well-defined phenotypes in addition to sufficient numbers of individuals with the appropriate pedigree structure from families and/or communities.

Animals↗

PubMed2002

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.

Adipose Tissue↗

PubMed2001

Analysis of the lamin A/C gene as a candidate for type II diabetes susceptibility in Pima Indians.

AIMS/HYPOTHESIS: Lamin A/C (LMNA) is located within a region on chromosome 1q that has been linked with Type II (non-insulin-dependent) diabetes mellitus in Pima Indians. Rare mutations in exon 8 of LMNA underlie Dunnigan-Type familial partial lipodystrophy, a disease characterized by regional adipocyte degeneration and frequently accompanied by insulin resistance, glucose intolerance, and diabetes. A more common variant in exon 10 (3408C/T) has recently been associated with obesity in non-diabetic aboriginal Canadian subjects. Because obesity is a strongly predisposing factor for Type II diabetes, we hypothesized that the LMNA 3408C/T variant could be associated with diabetes and body mass index in Pima Indians. METHODS: To determine whether the LMNA 3408C/T variant contributes to Type II diabetes susceptibility, we genotyped the polymorphism in 1,338 Pimas using allelic discrimination technology. The locus was screened for additional variants in 20 diabetic Pima Indians and non-diabetic Pima Indians using denaturing high performance liquid chromatography and dideoxy sequencing. RESULTS: We found no evidence for association of 3408C/T with diabetes, body mass index, total cholesterol, HDL cholesterol, triglycerides, leptin concentrations, or indices of insulin sensitivity and secretion. Subsequent screening of the remaining LMNA exons and flanking sequences revealed only rare variants in intron 4 and the 3'UTR, showing no frequency differences between diabetic and non-diabetic Pima Indians. We reassessed the linkage with diabetes following adjustment for the LMNA 3408C/T variant; adjustment for the effects of LMNA did not substantially modify the evidence for linkage. CONCLUSION/INTERPRETATION: We conclude that the LMNA 3408C/T variant probably does not play a role in susceptibility to diabetes or obesity in Pima Indians.

Alleles↗

PubMed2001

Single nucleotide polymorphisms of the fukutin gene.

Mutations in the LMNA gene, which encodes nuclear lamins A and C, underlie both Emery-Dreifuss muscular dystrophy (EMD2) and Dunnigan-type familial partial lipodystrophy (FPLD). This indicates that one gene can cause different phenotypes characterized by tissue degeneration. The gene for one form of Berardinelli-Seip-type congenital total lipodystrophy (BSCL) has been mapped to chromosome 9q34. Based on the observation that one gene caused both FPLD and EMD2, we considered that a known gene for muscular dystrophy at or near the BSCL locus on chromosome 9q would be an appropriate candidate for BSCL. The gene encoding fukutin, which is mutated in Fukuyama congenital muscular dystrophy has been mapped to 9q31. We thus developed amplification primers for the coding regions of the fukutin gene. We found no putative disease mutations, but through screening of diseased and normal subjects, we identified three novel single nucleotide polymorphisms (SNPs). We conclude that mutations in fukutin are not present in subjects with BSCL. However, the identification of SNPs provides tools to investigate this protein for association with other phenotypes.

Base Sequence↗

PubMed2001

Single-nucleotide polymorphisms of the nuclear lamina proteome.

Familial partial lipodystrophy (FPLD) has been shown to be due to mutations in the LMNA gene encoding nuclear lamins A and C, indicating that defective structure of the nuclear envelope can produce this unique phenotype. Some patients with inherited partial lipodystrophy have normal LMNA coding, promoter, and 3'-untranslated region sequences. This suggests that the FPLD phenotype is genetically heterogeneous. Among the candidate genes to consider for the non-LMNA-associated forms of FPLD are other components of the inner nuclear membrane, such as lamin B1 and B2 and the lamin B receptor. We developed amplification primers for the coding regions of LMNB1, LMNB2, and LBR, which encode lamin B1, lamin B2, and the lamin B receptor, respectively. We found no putative disease mutations in any of these proteins in subjects with non-LMNA FPLD, but, through the screening of diseased and normal subjects, we identified several single-nucleotide polymorphisms (SNPs); specifically, five SNPs in LMNB1 and four SNPs in LBR. The LMNB2 gene was monomorphic in screening experiments. We conclude that mutations in other constituent proteins of the nuclear envelope are not present in subjects with non-LMNA-associated FPLD. However, the identification of amplification primers and SNPs provides tools to investigate these proteins for their association with other phenotypes.

Base Sequence↗

PubMed2002

Identification of lamin A/C ( LMNA) gene mutations in Korean patients with autosomal dominant Emery-Dreifuss muscular dystrophy and limb-girdle muscular dystrophy 1B.

Mutations in the LMNA gene encoding lamins A and C by alternative splicing have been found to cause at least four different kinds of genetic disorders: autosomal dominant Emery-Dreifuss muscular dystrophy (EDMD2; MIM 181350); limb-girdle muscular dystrophy type 1B (LGMD1B; MIM 159001); dilated cardiomyopathy type 1A (CMD1A; MIM 115200); and familial partial lipodystrophy (FPLD; MIM 151660). Recently, we have studied two Korean patients with atrioventricular conduction defects. They had variable extents of muscular dystrophy; one patient was diagnosed with EDMD2 and the other with LGMD1B. We performed a mutation analysis of the LMNA gene by direct sequencing and found two different missense mutations: R249Q and R377L, in the EDMD2 and LGMD1B patient, respectively. The R249Q mutation is located within the central rod domain of the LMNA gene, and has been described in at least five unrelated sporadic EDMD2 patients. On the other hand, the R377L mutation, also located within the rod domain, is a novel mutation, although a histidine substitution instead of leucine (R377H) has been reported previously in an LGMD1B patient. To our knowledge, this is the first report of LMNA gene mutations in Korean patients with EDMD2 and LGMD1B.

Adult↗

PubMed2004

Both lamin A and lamin C mutations cause lamina instability as well as loss of internal nuclear lamin organization.

We have applied the fluorescence loss of intensity after photobleaching (FLIP) technique to study the molecular dynamics and organization of nuclear lamin proteins in cell lines stably transfected with green fluorescent protein (GFP)-tagged A-type lamin cDNA. Normal lamin A and C proteins show abundant decoration of the inner layer of the nuclear membrane, the nuclear lamina, and a generally diffuse localization in the nuclear interior. Bleaching studies revealed that, while the GFP-tagged lamins in the lamina were virtually immobile, the intranuclear fraction of these molecules was partially mobile. Intranuclear lamin C was significantly more mobile than intranuclear lamina A. In search of a structural cause for the variety of inherited diseases caused by A-type lamin mutations, we have studied the molecular organization of GFP-tagged lamin A and lamin C mutants R453W and R386K, found in Emery-Dreifuss muscular dystrophy (EDMD), and lamin A and lamin C mutant R482W, found in patients with Dunnigan-type familial partial lipodystrophy (FPLD). In all mutants, a prominent increase in lamin mobility was observed, indicating loss of structural stability of lamin polymers, both at the perinuclear lamina and in the intranuclear lamin organization. While the lamin rod domain mutant showed overall increased mobility, the tail domain mutants showed mainly intranuclear destabilization, possibly as a result of loss of interaction with chromatin. Decreased stability of lamin mutant polymers was confirmed by flow cytometric analyses and immunoblotting of nuclear extracts. Our findings suggest a loss of function of A-type lamin mutant proteins in the organization of intranuclear chromatin and predict the loss of gene regulatory function in laminopathies.

Animals↗

PubMed2003

The nuclear lamina and its functions in the nucleus.

The nuclear lamina is a structure near the inner nuclear membrane and the peripheral chromatin. It is composed of lamins, which are also present in the nuclear interior, and lamin-associated proteins. The increasing number of proteins that interact with lamins and the compound interactions between these proteins and chromatin-associated proteins make the nuclear lamina a highly complex but also a very exciting structure. The nuclear lamina is an essential component of metazoan cells. It is involved in most nuclear activities including DNA replication, RNA transcription, nuclear and chromatin organization, cell cycle regulation, cell development and differentiation, nuclear migration, and apoptosis. Specific mutations in nuclear lamina genes cause a wide range of heritable human diseases. These diseases include Emery-Dreifuss muscular dystrophy, limb girdle muscular dystrophy, dilated cardiomyopathy (DCM) with conduction system disease, familial partial lipodystrophy (FPLD), autosomal recessive axonal neuropathy (Charcot-Marie-Tooth disorder type 2, CMT2), mandibuloacral dysplasia (MAD), Hutchison Gilford Progeria syndrome (HGS), Greenberg Skeletal Dysplasia, and Pelger-Huet anomaly (PHA). Genetic analyses in Caenorhabditis elegans, Drosophila, and mice show new insights into the functions of the nuclear lamina, and recent structural analyses have begun to unravel the molecular structure and assembly of lamins and their associated proteins.

Animals↗

PubMed2000

Emery-Dreifuss muscular dystrophy - a 40 year retrospective.

Emery-Dreifuss muscular dystrophy (EDMD) was delineated as a separate form of muscular dystrophy nearly 40 years ago, based on the distinctive clinical features of early contractures and humero-peroneal weakness, and cardiac conduction defects. The gene, STA at Xq28, for the commoner X-linked EDMD encodes a 34 kD nuclear membrane protein designated 'emerin', and in almost all cases on immunostaining is absent in muscle, skin fibroblasts, leucocytes and even exfoliative buccal cells, and a mosaic pattern in female carriers. The gene, LMNA at 1q21, for the autosomal dominant Emery-Dreifuss muscular dystrophy encodes other nuclear membrane proteins, lamins A/C. The diagnosis (at present) depends on mutation analysis rather than protein immunohistochemistry. It is still not at all clear how defects in these nuclear membrane proteins are related to the phenotype, even less clear that LMNA mutations can also be associated with familial dilated cardiomyopathy with no weakness, and even familial partial lipodystrophy with diabetes mellitus and coronary heart disease! What began as clinical studies in a relatively rare form of dystrophy has progressed to detailed research into the functions of nuclear membrane proteins particularly in regard to various forms of heart disease.

Humans↗

PubMed2000

Lipoatrophy revisited.

The lipoatrophy syndromes are a heterogeneous group of syndromes characterized by a paucity of adipose tissue. Severe lipoatrophy is associated with insulin-resistant diabetes mellitus (DM). The loss of adipose tissue can have a genetic, immune, or infectious/drug-associated etiology. Causative mutations have been identified in patients for one form of partial lipoatrophy--Dunnigan-type familial partial lipodystrophy. Experiments using lipoatrophic mice demonstrate that the diabetes results from the lack of fat and that leptin deficiency is a contributing factor. Thiazolidinedione therapy improves metabolic control in lipoatrophic patients; the efficacy of leptin treatment is currently being investigated.

Adipose Tissue↗

PubMed2003

Monogenic forms of insulin resistance: apertures that expose the common metabolic syndrome.

Insulin resistance is common and plays a central role in the pathogenesis of type 2 diabetes mellitus (T2DM). Precedents in biomedical research indicate that evaluation of monogenic syndromes can help to understand a common complex phenotype. Monogenic forms of insulin resistance, such as familial partial lipodystrophy, which results from mutations in either LMNA (encoding lamin A/C) or PPARG (encoding peroxisome proliferator-activated receptor gamma), and congenital generalized lipodystrophy, which results from mutations in either AGPAT2 (encoding 1-acylglycerol-3-phosphate O-acyltransferase) or BSCL2 (encoding seipin), can display features seen in the common metabolic syndrome. In addition, insulin resistance is seen in disorders associated with insulin receptor mutations, progeria syndromes and in inherited forms of obesity. Although insulin resistance in such rare monogenic syndromes could simply be secondary to fat redistribution and/or central obesity, the products of the causative genes might also produce insulin resistance directly, and might illuminate new causative mechanisms for insulin resistance in such common disorders as T2DM and obesity.

Humans↗

PubMed2001

The A-type lamins: nuclear structural proteins as a focus for muscular dystrophy and cardiovascular diseases.

Mutations in the lamin A (LMNA) gene are associated with the tissue-specific diseases Emery-Dreifuss muscular dystrophy (EDMD), limb girdle muscular dystrophy (LGMD-1B), dilated cardiomyopathy with conduction system disease (DCM-CD), and Dunnigan's familial partial lipodystrophy (FPLD). Lamins A and C, the products of the LMNA gene, are nuclear intermediate filament proteins and are the major structural components of the lamina network that underlies and supports the nuclear envelope. Nuclear fragility and mislocalization of the nuclear envelope protein emerin are two defects induced by a lack of the A-type lamins. These observations reveal that organization and structural integrity of the nucleus are critical factors in the origins of certain dystrophic and cardiovascular diseases.

Animals↗

PubMed2002

Environmental modulation of atherosclerosis end points in familial hypercholesterolemia.

In familial hypercholesterolemia (FH), early coronary heart disease (CHD) is a complex trait that results from a large monogenic component of susceptibility due to elevated LDL cholesterol. This was demonstrated by observation of the high risk of early CHD in FH subjects compared with the general population. However, not all subjects with a LDLR gene mutation suffer with early CHD. Furthermore, studies in extended multigenerational families showed that even for this strong monogenic effect the environment could substantially modulate the age at death from CHD. Anecdotal examples of apparent modulation of atherosclerosis severity by lifestyle changes were also seen in other monogenic metabolic problems, such as hepatic lipase deficiency and Dunnigan-type familial partial lipodystrophy. Thus, even within apparently clear-cut rare monogenic metabolic diseases, such as FH, among carriers there can be a variability in the expression of important quantitative end points, such as early CHD. In some cases, the environment, including lifestyle factors, appears to play a key role in modulating the disease severity. This complexity could have implications for diagnosis and treatment.

Adult↗

PubMed2001

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.

Animals↗