EPHX1 mutations cause a lipoatrophic diabetes syndrome due to impaired epoxide hydrolysis and increased cellular senescence.

Epoxide hydrolases (EHs) regulate cellular homeostasis through hydrolysis of epoxides to less-reactive diols. The first discovered EH was EPHX1, also known as mEH. EH functions remain partly unknown, and no pathogenic variants have been reported in humans. We identified two de novo variants located in EPHX1 catalytic site in patients with a lipoatrophic diabetes characterized by loss of adipose tissue, insulin resistance, and multiple organ dysfunction. Functional analyses revealed that these variants led to the protein aggregation within the endoplasmic reticulum and to a loss of its hydrolysis activity. CRISPR-Cas9-mediated EPHX1 knockout (KO) abolished adipocyte differentiation and decreased insulin response. This KO also promoted oxidative stress and cellular senescence, an observation confirmed in patient-derived fibroblasts. Metreleptin therapy had a beneficial effect in one patient. This translational study highlights the importance of epoxide regulation for adipocyte function and provides new insights into the physiological roles of EHs in humans.

Early-onset, severe lipoatrophy in a patient with permanent neonatal diabetes mellitus secondary to a recessive mutation in the INS gene.

We describe a case of neonatal diabetes due to a homozygous mutation (c.3 G>T) at the INS gene, leading to lack of insulin expression and severe hyperglycemia from day one of life requiring permanent insulin replacement therapy. The genetic loss of endogenous insulin production likely led to lack of immune tolerance to insulin, with resultant autoantibody production against exogenous insulin and progressive immune-mediated lipoatrophy at injection sites.

Síndromes de insulino resistencia extrema / Extreme insulin resistance syndromes

Los síndromes de insulino resistencia extrema son entidades raras. Las formas monogénicas de las mismas están ligadas a mutaciones del recepto de insulina o de genes responsable de los síndromes lipoatróficos. Los tres síndromes relacionados con mutaciones del receptor de insulina son el síndrome A, el leprechaunismo y el de Rabson- Mendenhall. Los pacientes con la forma más severa, leprechaunismo, tiene retraso de crecimiento intrauterino, alteración del metabolismo hidrocarbonato y muerte precoz. El Rabson-Mendenhall es una forma menos grave con supervivencia de 5 a 15 años. Las dos formas principales de lipodistrofia congénita son la lipodistrofia congénita generalizada y la forma parcial familiar. En la primera tres loci han sido referidos: AGPAT2, BSCL2 y caveolin 1. En la segunda cuatro loci ha sido encontrados: Laminina A/C (LMNA), PPARG, V-AKT” y ZMPSTE23 (AU)

Extreme insulin resistance syndromes are rare entities. Genetically determined forms are mainly linked to mutations of the insulin receptor gene and to lipoatrophic syndrome-linked mutations. The three syndromes related to mutations of the insulin receptor gene are Type A syndrome, leprechaunism and Rabson- Mendenhall syndrome. Patientes with the more severe syndrome, leprechaunism, have growth restriction, altered glucose homeostasis and early death. Rabson-Mendenhall syndrome is less severe with survival up to 5-15 years of age. These disorders are transmitted as autosomal recessive traits. The two main types of genetic lipodystrophies are: congenital generalized lipodystrophy (CGL) and familial partial lipodys-trophy (FPL). So far, three genetic loci have been reported for CGL: AGPAT2, BSCL2 and caveolin 1 (CAV1) whereas for FPL, four loci have been discovered: lamin A/C (LMNA), PPARG, V-AKT2 and ZMPSTE24 (AU)

Adrenocortical changes and arterial hypertension in lipoatrophic A-ZIP/F-1 mice.

The A-ZIP/F-1 transgenic mouse is a model of lipoatrophic diabetes with severe insulin resistance, hyperglycemia and hyperlipidemia. Recently, a regulatory role of adipose tissue on adrenal gland function and blood pressure has been suggested. To further explore the importance of adipose tissue in the regulation of adrenal function and blood pressure, we studied this mouse model of lipodystrophy. A-ZIP/F-1 mice exhibit significantly elevated systolic and diastolic blood pressure values despite lack of white adipose tissue and its hormones. Furthermore, A-ZIP/F-1 lipoatrophic mice have a significant reduction of adrenal zona glomerulosa, while plasma aldosterone levels and aldosterone synthase mRNA expression remain unchanged. On the other hand, lipoatrophic mice present elevated corticosterone levels but no adrenocortical hyperplasia. Ultrastructural analysis of adrenal gland show significant alterations in adrenocortical cells, with conformational changes of mitochondrial internal membranes and high amounts of liposomes. In conclusion, lipodystrophy in A-ZIP/F-1 mice is associated with hypertension, possibly due to hypercorticosteronemia and/or others metabolic-vascular changes.

Sequencing of the reannotated LMNB2 gene reveals novel mutations in patients with acquired partial lipodystrophy.

The etiology of acquired partial lipodystrophy (APL, also called "Barraquer-Simons syndrome") is unknown. Genomic DNA mutations affecting the nuclear lamina protein lamin A cause inherited partial lipodystrophy but are not found in patients with APL. Because it also encodes a nuclear lamina protein (lamin B2) and its genomic structure was recently reannotated, we sequenced LMNB2 as a candidate gene in nine white patients with APL. In four patients, we found three new rare mutations in LMNB2: intron 1 -6G-->T, exon 5 c.643G-->A (p.R215Q; in two patients), and exon 8 c.1218G-->A (p.A407T). The combined frequency of these mutations was 0.222 in the patients with APL, compared with 0.0018 in a multiethnic control sample of 1,100 subjects (P = 2.1 x 10-7) and 0.0045 in a sample of 330 white controls (P = 1.2 x 10-5). These novel heterozygous mutations are the first reported for LMNB2, are the first reported among patients with APL, and indicate how sequencing of a reannotated candidate gene can reveal new disease-associated mutations.

Berardinelli-Seip congenital lipodystrophy.

Berardinelli-Seip congenital lipodystrophy (BSCL) is a very rare genetic disorder characterized by lipoatrophy, hypertriglyceridemia, hepatomegaly and acromegaloid features. On the basis of mutational and haplotype analysis, BSCL families have been classified into three types BSCL 1, BSCL2 and BSCLX. We report Berardinelli-Seip congenital lipodystrophy (BSCL2 type) in three subjects from two unrelated Indian families (family1 and family2). The mutation (c.IVS2 11 A GT G ) found in affected members of family1 is a newly identified mutation. We also report the association of renal anomaly with this new mutation.

A LMNA splicing mutation in two sisters with severe Dunnigan-type familial partial lipodystrophy type 2.

CONTEXT: To date, all cases of familial partial lipodystrophy type 2 (FPLD2; Mendelian Inheritance in Man 151660) result from missense mutations in LMNA, which encodes nuclear lamin A/C (Mendelian Inheritance in Man 150330). OBJECTIVE: The objective of the study was to carry out mutational analysis of LMNA in two sisters with a particularly severe FPLD2 phenotype. DESIGN: This was a descriptive case report with molecular studies. SETTING: The study was conducted at a referral center. PATIENTS: We report two sisters of South Asian origin. The first presented with acanthosis nigricans at age 5 yr, diabetes with insulin resistance, hypertension and hypertriglyceridemia at age 13 yr, and partial lipodystrophy starting at puberty. Her sister and their mother had a similar metabolic profile and physical features, and their mother died of vascular disease at age 32 yr. INTERVENTIONS: There were no interventions. MAIN OUTCOME MEASURES AND RESULTS: LMNA sequencing showed that the sisters were each heterozygous for a novel G>C mutation at the intron 8 consensus splice donor site, which was absent from the genomes of 300 healthy individuals. The retention of intron 8 in mRNA predicted a prematurely truncated lamin A isoform (516 instead of 664 amino acids) with 20 nonsense 3'-terminal residues. The mutant lamin A isoform failed to interact normally with emerin and failed to localize to the nuclear envelope. CONCLUSIONS: This is the first LMNA splicing mutation to be associated with FPLD2, and it causes a severe clinical and metabolic phenotype.

Membrane topology of the human seipin protein.

The Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) gene encodes an integral membrane protein, called seipin, of unknown function localized to the endoplasmic reticulum of eukaryotic cells. Seipin is associated with the heterogeneous genetic disease BSCL2, and mutations in an N-glycosylation motif links the protein to two other disorders, autosomal-dominant distal hereditary motor neuropathy type V and Silver syndrome. Here, we report a topological study of seipin using an in vitro topology mapping assay. Our results suggest that the predominant form of seipin is 462 residues long and has an N(cyt)-C(cyt) orientation with a long luminal loop between the two transmembrane helices.

Peroxisomal proliferator activated receptor-gamma deficiency in a Canadian kindred with familial partial lipodystrophy type 3 (FPLD3).

BACKGROUND: Familial partial lipodystrophy (Dunnigan) type 3 (FPLD3, Mendelian Inheritance in Man [MIM] 604367) results from heterozygous mutations in PPARG encoding peroxisomal proliferator-activated receptor-gamma. Both dominant-negative and haploinsufficiency mechanisms have been suggested for this condition. METHODS: We present a Canadian FPLD3 kindred with an affected mother who had loss of fat on arms and legs, but no increase in facial, neck, suprascapular or abdominal fat. She had profound insulin resistance, diabetes, severe hypertriglyceridemia and relapsing pancreatitis, while her pre-pubescent daughter had normal fat distribution but elevated plasma triglycerides and C-peptide and depressed high-density lipoprotein cholesterol. RESULTS: The mother and daughter were each heterozygous for PPARG nonsense mutation Y355X, whose protein product in vitro was transcriptionally inactive with no dominant-negative activity against the wild-type receptor. In addition the mutant protein appeared to be markedly unstable. CONCLUSION: Taken together with previous studies of human PPARG mutations, these findings suggest that PPAR-gamma deficiency due either to haploinsufficiency or to substantial activity loss due to dominant negative interference of the normal allele product's function can each contribute to the FPLD3 phenotype.

Nuclear lamin A inhibits adipocyte differentiation: implications for Dunnigan-type familial partial lipodystrophy.

Mutations in the LMNA gene encoding A-type lamins cause several diseases, including Emery-Dreifuss muscular dystrophy and Dunnigan-type familial partial lipodystrophy (FPLD). We analyzed differentiation of 3T3-L1 preadipocytes to adipocytes in cells overexpressing wild-type lamin A as well as lamin A with amino acid substitutions at position 482 that cause FPLD. We also examined adipogenic conversion of mouse embryonic fibroblasts lacking A-type lamins. Overexpression of both wild-type and mutant lamin A inhibited lipid accumulation, triglyceride synthesis and expression of adipogenic markers. This was associated with inhibition of expression of peroxisome-proliferator-activated receptor gamma 2 (PPARgamma2) and Glut4. In contrast, embryonic fibroblasts lacking A-type lamins accumulated more intracellular lipid and exhibited elevated de novo triglyceride synthesis compared with wild-type fibroblasts. They also had increased basal phosphorylation of AKT1, a mediator of insulin signaling. We conclude that A-type lamins act as inhibitors of adipocyte differentiation, possibly by affecting PPARgamma2 and insulin signaling.

Mouse models created to study the pathophysiology of Type 2 diabetes.

Obesity and Type 2 diabetes have become epidemics in the Western world. Understanding the pathophysiology of the disease should help in prevention and treatment of these disorders. A common theme is the presence of insulin resistance that eventually results in Type 2 diabetes. To understand the underlying mechanisms in the progression of the disease states, investigators have created mouse models by transgenic overexpression of a candidate gene or produced gene-deletion mouse models. This review will summarize many of the more appropriate models that study insulin resistance and Type 2 diabetes.

Adipokines and the insulin resistance syndrome in familial partial lipodystrophy caused by a mutation in lamin A/C.

AIMS/HYPOTHESIS: Familial partial lipodystrophy (FPLD) and obesity are both associated with increased risks of type 2 diabetes and cardiovascular disease. Although adipokines have been implicated, few data exist in subjects with FPLD; therefore we investigated a family with FPLD due to a lamin A/C mutation in order to determine how abnormalities of the plasma adipokine profile relate to insulin resistance and the metabolic syndrome. METHODS: Plasma levels of adiponectin, leptin, resistin, IL-1beta, IL-6 and TNF-alpha in 30 subjects (ten patients, 20 controls) were correlated with indices of metabolic syndrome. RESULTS: Compared with controls, FPLD patients had significantly lower plasma levels of adiponectin (3.7+/-1.0 in FDLP cases vs 7.1+/-0.72 mug/ml in controls, p=0.02), leptin (1.23+/-0.4 vs 9.0+/-1.3 ng/ml, p=0.002) and IL-6 (0.59+/-0.12 vs 1.04+/-0.17 pg/ml, p=0.047) and elevated TNF-alpha (34.8+/-8.1 vs 13.7+/-2.7 pg/ml, p=0.028), whereas IL-1beta and resistin were unchanged. In both groups, adiponectin levels were inversely correlated with body fat mass (controls, r=-0.44, p=0.036; FDLP, r=-0.67, p=0.025), insulin resistance (controls, r=-0.62, p=0.003; FDLP, r=-0.70, p=0.025) and other features of the metabolic syndrome. TNF-alpha concentrations were positively related to fat mass (controls, r=0.68, p=0.001; FDLP, r=0.64, p=0.048) and insulin resistance (controls, r=0.86, p=0.001; FDLP, r=0.75, p=0.013). IL-6, IL-1beta and resistin did not demonstrate any correlations with the metabolic syndrome in either group. CONCLUSIONS/INTERPRETATION: Low adiponectin and leptin and high TNF-alpha were identified as the major plasma adipokine abnormalities in FPLD, consistent with the hypothesis that low adiponectin and high TNF-alpha production may be mechanistically related, and perhaps responsible for the development of insulin resistance and cardiovascular disease in FPLD.

Diseases of adipose tissue: genetic and acquired lipodystrophies.

Human lipodystrophies represent a group of diseases characterized by altered body fat amount and/or repartition and major metabolic alterations with insulin resistance leading to diabetic complications and increased cardiovascular and hepatic risk. Genetic forms of lipodystrophies are rare. Congenital generalized lipodystrophy or Berardinelli-Seip syndrome, autosomal recessive, is characterized by a complete early lipoatrophy and severe insulin resistance and results, in most cases, from mutations either in the seipin gene of unknown function or AGPAT2 encoding an enzyme involved in triacylglycerol synthesis. The Dunnigan syndrome [FPLD2 (familial partial lipodystrophy of the Dunnigan type)] is due to mutations in LMNA encoding the lamin A/C, belonging to the complex group of laminopathies that could comprise muscular and cardiac dystrophies, neuropathies and syndromes of premature aging. Some FPLDs are linked to loss-of-function mutations in the PPAR-gamma gene (peroxisome-proliferator-activated receptor gamma; FPLD3) with severe metabolic alterations but a less severe lipodystrophy compared with FPLD2. The metabolic syndrome, acquired, represents the most common form of lipodystrophy. HIV-infected patients often present lipodystrophies, mainly related to side effects of antiretroviral drugs together with insulin resistance and metabolic alterations. Such syndromes help to understand the mechanisms involved in insulin resistance resulting from altered fat repartition and could benefit from insulin-sensitizing effects of lifestyle modifications or of specific medications.

Hepatic steatosis in Dunnigan-type familial partial lipodystrophy.

OBJECTIVES: Characterization of familial clusters of subjects with metabolic derangements predisposing to hepatic steatosis and nonalcoholic steatohepatitis could facilitate genomic studies to identify risk factors for their development. Dunnigan-type familial partial lipodystrophy (FPLD) is an autosomal dominantly inherited disorder caused by mutations in the LMNA gene. Affected subjects have loss of subcutaneous fat from the extremities and symptoms similar to those characterizing the metabolic syndrome, including insulin resistance and dyslipidemia. The goal of this study was to determine the prevalence of steatosis in subjects with FPLD. METHODS: We examined 18 subjects from six families with FPLD for mutations in LMNA and analyzed plasma lipid and serum glucose concentrations. Liver ultrasound and serum aminotransferase activities were used as indicators of steatosis or steatohepatitis. In two subjects, histological examination of hepatic tissue was performed. RESULTS: All subjects had FPLD-causing mutations in LMNA. Plasma lipids were measured in 17 subjects, 16 of whom had hyperlipidemia and 14 presented with either documented insulin resistance or diabetes mellitus. Hepatic steatosis was present in 15 subjects who had ultrasound examinations and 9 of these had elevated serum aminotransferase activities. Liver biopsy confirmed steatosis in 2 subjects. CONCLUSIONS: Hepatic steatosis is part of the clinical phenotype of FPLD. This familial disorder may provide a human metabolic model system to facilitate genomic and environmental studies to determine risk factors for hepatic steatosis and nonalcoholic steatohepatitis.

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.

Genetic modulation of senescent phenotypes in Homo sapiens.

Single-gene mutations can produce human progeroid syndromes--phenotypes that mimic usual or "normative" aging. These can be divided into two classes--those that have their impacts upon multiple organs and tissues (segmental progeroid syndromes) and those that have their major impacts upon a single organ or tissue (unimodal progeroid syndromes). The prototypic example of the former is the Werner syndrome, a condition caused by mutations of the RecQ family of DNA helicases. Research on the Werner syndrome and a surprising number of other progeroid syndromes support the importance of the maintenance of genomic stability as a partial antidote to aging. The prototypic examples of the latter are Alzheimer type dementias. The three gene products that cause rare autosomal-dominant early-onset varieties of these disorders all participate in the modulation of the beta amyloid precursor protein. They thus support the importance of the maintenance of proper protein processing and folding as a partial antidote to aging.

Phenotypes of the N88S Berardinelli-Seip congenital lipodystrophy 2 mutation.

Recently, two missense mutations (N88S, S90L) in the Berardinelli-Seip congenital lipodystrophy gene have been identified in autosomal dominant distal hereditary motor neuropathy and Silver syndrome. We report the phenotypic consequences of the N88S mutation in 90 patients of 1 large Austrian family and two unrelated German families. Variation in the clinical and electrophysiological phenotype enabled us to distinguish six subtypes. In 4.4%, the disorder was not penetrant. Twenty percent of the patients were subclinically affected; some of these patients could only be detected by pathological nerve conduction studies. A distal hereditary motor neuropathy type V phenotype characterized by predominant hand muscle involvement was found in 31.1%, whereas 14.5% showed typical Silver syndrome with amyotrophy of the small hand muscles and spasticity of the lower extremities. Moreover, the phenotype present in 20% was compatible with Charcot-Marie-Tooth disease. In 10%, the clinical diagnosis of pure or complicated hereditary spastic paraparesis was made. Electrophysiological studies showed an axonal neuropathy but also chronodispersion of compound motor action potentials and conduction blocks. Sensory nerve conduction studies were rarely pathological. Our study indicates that the dominant N88S mutation in the Berardinelli-Seip congenital lipodystrophy gene 2 leads to a broad spectrum of motor neuron disorders.

Phenotypic heterogeneity in biochemical parameters correlates with mutations in AGPAT2 or Seipin genes among Berardinelli-Seip congenital lipodystrophy patients.

The Berardinelli-Seip congenital lipodystrophy (BSCL) syndrome is characterized by a near-total congenital absence of fat and predisposition to develop diabetes mellitus. We have previously reported that 22 patients from 16 consanguineous pedigrees living in the northeastern region of Brazil had a homozygous 669insA mutation in the Seipin gene (BSCL2 locus), while all of the 10 investigated subjects from the southeastern region were homozygous for a 1036 bp deletion in the AGPAT2 gene (BSCL1 locus). In this study, we compared the serum insulin and insulin resistance (HOMA), leptin, triglyceride and fasting glucose levels in individuals of these two genetically distinct clusters of BSCL subjects. The onset of diabetes was also estimated. The fasting glucose and triglyceride levels were not significantly different in these groups. Significant differences were detected for leptin, insulin and insulin resistance. BSCL1 patients presented lower serum leptin levels compared to BSCL2 patients. BSCL2 subjects had earlier onset of diabetes and higher insulin levels. In agreement, BSCL2 patients were more insulin resistant, as detected by HOMA. These results indicate phenotypic heterogeneity between BSCL1 and BSCL2 Brazilian subjects.