Prevalence of mutations in AGPAT2 among human lipodystrophies

Lipid droplet biogenesis and functions in health and disease

Ubiquitous yet unique, lipid droplets are intracellular organelles that are increasingly being recognized for their versatility beyond energy storage. Advances uncovering the intricacies of their biogenesis and the diversity of their physiological and pathological roles have yielded new insights into lipid droplet biology. Despite these insights, the mechanisms governing the biogenesis and functions of lipid droplets remain incompletely understood. Moreover, the causal relationship between the biogenesis and function of lipid droplets and human diseases is poorly resolved. Here, we provide an update on the current understanding of the biogenesis and functions of lipid droplets in health and disease, highlighting a key role for lipid droplet biogenesis in alleviating cellular stresses. We also discuss therapeutic strategies of targeting lipid droplet biogenesis, growth or degradation that could be applied in the future to common diseases, such as cancer, hepatic steatosis and viral infection.

Face-sparing Congenital Generalized Lipodystrophy Type 1 Associated With Nonclassical Congenital Adrenal Hyperplasia

CONTEXT

Congenital generalized lipodystrophy, type 1 (CGL1), due to biallelic pathogenic variants in AGPAT2, is characterized by the near total loss of body fat from the face, trunk, and extremities. Patients develop premature diabetes, hypertriglyceridemia, hepatic steatosis, and polycystic ovary syndrome. However, sparing of the facial fat and precocious pubertal development has not been previously reported in CGL1.

CASE DESCRIPTION

We report a 21-year-old woman of European descent with CGL1 who had sparing of the facial fat and premature thelarche at birth with premature pubarche and menstrual bleeding at age 3 years. Her serum 17-OH progesterone level rose to 1000 ng/dL (30.26 nmol/L) after cosyntropin stimulation test, suggestive of nonclassical congenital adrenal hyperplasia (NCAH) due to 21-hydroxylase deficiency. Hydrocortisone replacement therapy from age 3.5 to 10 years resulted in cessation of menstruation and growth of pubic hair, and a reduction of breast size. Sanger and whole-exome sequencing revealed compound heterozygous variants c.493-1G>C; p.(Leu165_Gln196del), and c.del366_588+534; p.(Leu123Cysfs*55) in AGPAT2 plus c.806G>C; p.(Ser269Thr) and c.844G>T; p.(Val282Leu) in CYP21A2. She developed diabetes at age 13 requiring high-dose insulin and had 7 episodes of acute pancreatitis due to extreme hypertriglyceridemia in the next 5 years. Metreleptin therapy was initiated at age 18 and after 3 years, she had remission of diabetes and hypertriglyceridemia; however, menstrual irregularity and severe hirsutism did not improve.

CONCLUSION

Concomitant NCAH in this CGL1 patient was associated with precocious pubertal development and sparing of facial fat. Metreleptin therapy drastically improved her hyperglycemia and hyperlipidemia but not menstrual irregularity and hirsutism.

Approach to Diagnosing a Pediatric Patient With Severe Insulin Resistance in Low- or Middle-income Countries

Diabetes mellitus (DM) in children is most often caused by impaired insulin secretion (type 1 DM). In some children, the underlying mechanism for DM is increased insulin resistance, which can have different underlying causes. While the majority of these children require insulin dosages less than 2.0 U/kg/day to achieve normoglycemia, higher insulin requirements indicate severe insulin resistance. Considering the therapeutic challenges in patients with severe insulin resistance, early diagnosis of the underlying cause is essential in order to consider targeted therapies and to prevent diabetic complications. Although rare, several disorders can attribute to severe insulin resistance in pediatric patients. Most of these disorders are diagnosed through advanced diagnostic tests, which are not commonly available in low- or middle-income countries. Based on a case of DM with severe insulin resistance in a Surinamese adolescent who was later confirmed to have autosomal recessive congenital generalized lipodystrophy, type 1 (Berardinelli-Seip syndrome), we provide a systematic approach to the differential diagnosis and work-up. We show that a thorough review of medical history and physical examination generally provide sufficient information to diagnose a child with insulin-resistant DM correctly, and, therefore, our approach is especially applicable to low- or middle-income countries.

RNA-seq of peripheral blood mononuclear cells of congenital generalized lipodystrophy type 2 patients

Illumina RNA-seq analysis was used to characterize the whole transcriptomes of peripheral blood mononuclear cells (PBMCs) from patients with congenital generalized lipodystrophy. RNA-seq information for seven patients with type 2 congenital generalized lipodystrophy (CGL2; Berardinelli-Seip congenital lipodystrophy, BSCL2) was obtained and compared with similar information for seven age- and sex-matched healthy control subjects. All seven CGL2 patients carried biallelic pathogenic mutations affecting the BSCL2 gene and had clinical symptoms of varying severity. The findings provide the whole-transcriptome signatures of PBMCs of CGL2 patients, allowing further exploration of gene expression patterns/signatures associated with the various clinical symptoms of patients with this disease.

Measurement(s)	RNA-Seq • RNA
Technology Type(s)	Illumina HiSeq. 2500 • RNA sequencing
Sample Characteristic - Organism	Homo sapiens

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.15022521

Severe insulin resistance syndromes

Severe insulin resistance syndromes are a heterogeneous group of rare disorders characterized by profound insulin resistance, substantial metabolic abnormalities, and a variety of clinical manifestations and complications. The etiology of these syndromes may be hereditary or acquired, due to defects in insulin potency and action, cellular responsiveness to insulin, and/or aberrations in adipose tissue function or development. Over the past decades, advances in medical technology, particularly in genomic technologies and genetic analyses, have provided insights into the underlying pathophysiological pathways and facilitated the more precise identification of several of these conditions. However, the exact cellular and molecular mechanisms of insulin resistance have not yet been fully elucidated for all syndromes. Moreover, in clinical practice, many of the syndromes are often misdiagnosed or underdiagnosed. The majority of these disorders associate with an increased risk of severe complications and mortality; thus, early identification and personalized clinical management are of the essence. This Review aims to categorize severe insulin resistance syndromes by disease process, including insulin receptor defects, signaling defects, and lipodystrophies. We also highlight several complex syndromes and emphasize the need to identify patients, investigate underlying disease mechanisms, and develop specific treatment regimens.

Targeted massively parallel sequencing for congenital generalized lipodystrophy

Objective

Our aim is to establish genetic diagnosis of congenital generalized lipodystrophy (CGL) using targeted massively parallel sequencing (MPS), also known as next-generation sequencing (NGS).

Methods

Nine unrelated individuals with a clinical diagnosis of CGL were recruited. We used a customized panel to capture genes related to genetic lipodystrophies. DNA libraries were generated, sequenced using the Illumina MiSeq, and bioinformatics analysis was performed.

Results

An accurate genetic diagnosis was stated for all nine patients. Four had pathogenic variants in AGPAT2 and three in BSCL2. Three large homozygous deletions in AGPAT2 were identified by copy-number variant analysis.

Conclusion

Although we have found allelic variants in only 2 genes related to CGL, the panel was able to identify different variants including deletions that would have been missed by Sanger sequencing. We believe that MPS is a valuable tool for the genetic diagnosis of multi-genes related diseases, including CGL.

Acromegaly with congenital generalized lipodystrophy - two rare insulin resistance conditions in one patient: a case report

BACKGROUND

Lipodystrophies are a group of diseases which are characterized by abnormal adipose tissue deposition and are frequently associated with metabolic changes. Congenital generalized lipodystrophy is an autosomal recessive syndrome, with a prevalence < 1:10 million. Acromegaly is a rare disease, secondary to the chronic hypersecretion of growth hormone and insulin-like growth factor-1, with characteristic metabolic and somatic effects. "Acromegaloidism" is a term used for patients who manifest clinical features of acromegaly, but do not present a demonstrable hormone growth hypersecretion. The extreme shortage of subcutaneous adipose tissues and muscle hypertrophy confer an acromegaloid-like appearance in these patients.

CASE PRESENTATION

We describe a case of a patient with the rare combination of Berardinelli-Seip congenital lipodystrophy and acromegaly; our patient is a 63-year-old white man, who was referred to an endocrinology consultation for suspected lipodystrophy. He had lipoatrophy of upper and lower limbs, trunk, and buttocks, with muscular prominence, acromegaloid facial appearance, large extremities, and soft tissue tumescence. In addition, he had dyslipidemia and prediabetes. His fat mass ratio (% trunk fat mass/% lower limbs fat mass) was 1.02 by densitometry and he also had hepatomegaly, with mild steatosis (from an abdominal ultrasound), and left ventricular hypertrophy (from an electrocardiogram). His first oral glucose tolerance test had growth hormone nadir of 0.92 ng/mL, and the second test, 10 months afterwards, registered growth hormone nadir of 0.64 ng/mL (growth hormone nadir < 0.3 ng/mL excludes acromegaly). Pituitary magnetic resonance imaging identified an area of hypocaptation of contrast product in relation to a pituitary adenoma and he was subsequently submitted to transsphenoidal surgical resection of the mass. A pathological evaluation showed pituitary adenoma with extensive expression of growth hormone and adrenocorticotropic hormone, as well as a rare expression of follicle-stimulating hormone and prolactin. A genetic study revealed an exon 3/exon 4 deletion of the AGPAT2 gene in homozygosity.

CONCLUSIONS

Congenital generalized lipodystrophy is a rare disease which occurs with acromegaloid features. As far as we know, we have described the first case of genetic lipodystrophy associated with true acromegaly. Although this is a rare association, the presence of congenital generalized lipodystrophy should not exclude the possibility of simultaneous acromegaly.

Congenital Generalized Lipoatrophy (Berardinelli-Seip Syndrome) Type 1: Description of Novel AGPAT2 Homozygous Variants Showing the Highly Heterogeneous Presentation of the Disease

Berardinelli-Seip congenital lipoatrophy (BSCL) is characterized by near total fat atrophy, associated with the progressive development of metabolic complications. BSCL type 1 (BSCL1) is caused by mutations in AGPAT2, encoding 1-acylglycerol-3phosphate-O-acyltransferase β (recently renamed lysophosphatidic acid acyltransferase beta), which catalyzes the transformation of lysophosphatidic acid in phosphatidic acid, the precursor of glycerophospholipids and triglycerides. BSCL1 is an autosomal recessive disease due to AGPAT2 pathogenic variants leading to a depletion of triglycerides inside the adipose organ, and to a defective signaling of key elements involved in proper adipogenesis. We herein investigated the characteristics of two AGPAT2 variants in Caucasian Italian patients with Berardinelli-Seip congenital lipoatrophy. The first patient exhibited a novel homozygous nonsense c.430 C > T AGPAT2 mutation (p.Gln144^*) predicting the synthesis of a truncated enzyme of approximately half of the proper size. The second patient harbored a homozygous AGPAT2 missense variant (p.Arg159Cys), never described previously in BSCL1 patients: the segregation of the disease with the mutation in the pedigree of the family and the in silico analysis are compatible with a causative role of the p.Arg159Cys variant. We remark that BSCL1 can be clinically very heterogeneous at presentation and that the associated complications, occurring in the natural history of the disease, reduce life-expectancy. We point to the necessity for medical treatments capable of reducing the risk of cardiovascular death. In BSCL1 patients, the assessment of cardiovascular disease with conventional diagnostic means maybe particularly challenging.

What lipodystrophies teach us about the metabolic syndrome

Lipodystrophies are the result of a range of inherited and acquired causes, but all are characterized by perturbations in white adipose tissue function and, in many instances, its mass or distribution. Though patients are often nonobese, they typically manifest a severe form of the metabolic syndrome, highlighting the importance of white fat in the "safe" storage of surplus energy. Understanding the molecular pathophysiology of congenital lipodystrophies has yielded useful insights into the biology of adipocytes and informed therapeutic strategies. More recently, genome-wide association studies focused on insulin resistance have linked common variants to genes implicated in adipose biology and suggested that subtle forms of lipodystrophy contribute to cardiometabolic disease risk at a population level. These observations underpin the use of aligned treatment strategies in insulin-resistant obese and lipodystrophic patients, the major goal being to alleviate the energetic burden on adipose tissue.

The Structure and Function of Acylglycerophosphate Acyltransferase 4/ Lysophosphatidic Acid Acyltransferase Delta (AGPAT4/LPAATδ)

Lipid-modifying enzymes serve crucial roles in cellular processes such as signal transduction (producing lipid-derived second messengers), intracellular membrane transport (facilitating membrane remodeling needed for membrane fusion/fission), and protein clustering (organizing lipid domains as anchoring platforms). The lipid products crucial in these processes can derive from different metabolic pathways, thus it is essential to know the localization, substrate specificity, deriving products (and their function) of all lipid-modifying enzymes. Here we discuss an emerging family of these enzymes, the lysophosphatidic acid acyltransferases (LPAATs), also known as acylglycerophosphate acyltransferases (AGPATs), that produce phosphatidic acid (PA) having as substrates lysophosphatidic acid (LPA) and acyl-CoA. Eleven LPAAT/AGPAT enzymes have been identified in mice and humans based on sequence homologies, and their localization, specific substrates and functions explored. We focus on one member of the family, LPAATδ, a protein expressed mainly in brain and in muscle (though to a lesser extent in other tissues); while at the cellular level it is localized at the trans-Golgi network membranes and at the mitochondrial outer membranes. LPAATδ is a physiologically essential enzyme since mice knocked-out for Lpaatδ show severe dysfunctions including cognitive impairment, impaired force contractility and altered white adipose tissue. The LPAATδ physiological roles are related to the formation of its product PA. PA is a multifunctional lipid involved in cell signaling as well as in membrane remodeling. In particular, the LPAATδ-catalyzed conversion of LPA (inverted-cone-shaped lipid) to PA (cone-shaped lipid) is considered a mechanism of deformation of the bilayer that favors membrane fission. Indeed, LPAATδ is an essential component of the fission-inducing machinery driven by the protein BARS. In this process, a protein-tripartite complex (BARS/14-3-3γ/phosphoinositide kinase PI4KIIIβ) is recruited at the trans-Golgi network, at the sites where membrane fission is to occur; there, LPAATδ directly interacts with BARS and is activated by BARS. The resulting formation of PA is essential for membrane fission occurring at those spots. Also in mitochondria PA formation has been related to fusion/fission events. Since PA is formed by various enzymatic pathways in different cell compartments, the BARS-LPAATδ interaction indicates the relevance of lipid-modifying enzymes acting exactly where their products are needed (i.e., PA at the Golgi membranes).

The worldwide mutational landscape of Berardinelli-Seip congenital lipodystrophy

Berardinelli-Seip congenital lipodystrophy (BSCL) is a rare disease characterized by the near total absence of body fat at birth. BSCL etiology involves genetic variations in four different genes: AGPAT2, BSCL2, CAV1, and CAVIN1. The four different biochemical subtypes of the disease are distinguished depending on which gene is mutated. The diagnosis of lipodystrophy can be based on clinical criteria, but the gold standard remains genetic testing. Since many different mutations have already been correlated with the onset of the disease, the most indicative method is DNA sequencing. However, not all laboratories have the resources to perform sequencing. Thus, less expensive techniques that include narrow gene regions may be applied. In such cases, the target mutations to be tested must be carefully determined taking into account the frequency of the description of the mutations in the literature, the nationality of the patient, as well as their phenotype. This review considers the molecular basis of BSCL, including the manual count of the majority of mutations reported in the literature up to the year 2018. Ninety different genetic mutations in 332 cases were reported at different frequencies. Some mutations were distributed homogeneously and others were specific to geographic regions. Type 2 BSCL was mentioned most often in the literature (50.3% of the cases), followed by Type 1 (38.0%), Type 4 (10.2%), and Type 3 (1.5%). The mutations comprised frameshifts (34.4%), nonsense (26.6%), and missense (21.1%). The c.517dupA in the BSCL2 gene was the most frequent (13.3%), followed by c.589-2A>G in the AGPAT2 gene (11.5%), c.507_511delGTATC in the BSCL2 gene (9.7%), c.317-588del in the AGPAT2 gene (7.3%), and c.202C>T in the AGPAT2 gene (4.5%). This information should prove valuable for analysts in making decisions regarding the best therapeutic targets in a population-specific context, which will benefit patients and enable faster and less expensive treatment.

Monogenic forms of lipodystrophic syndromes: diagnosis, detection, and practical management considerations from clinical cases

BACKGROUND

Lipodystrophic syndromes are rare diseases of genetic or acquired origin characterized by partial or generalized lack of body fat. Early detection and diagnosis are crucial to prevent and manage associated metabolic dysfunctions, i.e. insulin resistance, dyslipidemia, fatty liver, and diabetes, and to provide appropriate genetic counseling. By means of several representative case studies, this article illustrates the diagnostic and management challenges of lipodystrophic syndromes.

REVIEW

Berardinelli-Seip congenital lipodystrophy (BSCL) is typically diagnosed at birth, or soon thereafter, with generalized lipoatrophy and hepatomegaly secondary to hepatic steatosis. Physicians must also consider this diagnosis in adults with atypical non-autoimmune diabetes, hypertriglyceridemia, and a lean and muscular phenotype. The BSCL1 subtype due to mutations in the AGPAT2 gene can have an unusual presentation, especially in neonates and infants. Particular attention should be paid to infants presenting failure to thrive who also have hepatomegaly and metabolic derangements. The BSCL2 sub-type due to mutations in the BSCL gene tends to be more severe than BSCL1, and is characterized by greater fat loss, mild intellectual disability, earlier onset of diabetes, and higher incidence of premature death. Effective management from an earlier age may moderate the natural disease course. Partial lipodystrophies may easily be confused with common central obesity and/or metabolic syndrome. In patients with unexplained pancreatitis and hypertriglyceridemia, lipodystrophies such as familial partial lipodystrophy type 2 (FPLD2; Dunnigan type, due to LMNA mutations) should be considered. Oral combined contraceptives, which can reveal the disease by inducing severe hypertriglyceridemia, are contraindicated. Endogenous estrogens may also lead to "unmasking" of the FPLD2 phenotype, which often appears at puberty, and is more severe in females than males.

CONCLUSIONS

Diet and exercise, adapted to age and potential comorbidities, are essential prerequisites for therapeutic management of lipodystrophic syndromes. Metreleptin therapy can be useful to manage lipodystrophy-related metabolic complications.

A New Compound Heterozygous Mutation Of BSCL2 In A Chinese Zhuang Ethnic Family With Congenital Generalized Lipodystrophy

PURPOSE

This study aims to report the clinical features of an infant with CGL in a Chinese Zhuang ethnic family, whose family members were discovered to carry new pathogenic mutations in the BSCL2.

PATIENTS AND METHODS

In this study, we report clinical and molecular investigations of CGL disease in a family of 4 members (parents and two sons). We used whole exome sequencing (WES) in the family to examine the genetic cause of the disease.

RESULTS

The proband presented with skin pigmentation, hypertriglyceridemia and diabetes. WES identified a previously unreported compound heterozygous mutation in the BSCL2 (c.545_546insCCG heterozygous mutation and exon 3 heterozygous deletion) in the proband. His mother is a heterozygous carrier of the c.545_546insCCG mutation and his father and brother are carriers of the exon 3 heterozygous deletion.

CONCLUSION

Compound heterozygous mutation of the BSCL2 (new c.545_546insCCG heterozygous mutation and new exon 3 heterozygous deletion) was detected in the proband with characteristic clinical manifestations of CGL2.

Further delineation of AGPAT2 and BSCL2 related congenital generalized lipodystrophy in young infants

BACKGROUND AND OBJECTIVES

Congenital generalized lipodystrophy (CGL) is a rare autosomal recessive disorder with two major subtypes, which are caused by AGPAT2 and BSCL2 mutations. Our aim was to further investigate the genetic features and clinical characteristics of infant patients with CGL.

PATIENTS AND METHODS

Three male infants and two female infants aged from one month to three months and unrelated with each other were involved in this study. Both whole-exome and Sanger sequencing were conducted, and variants were compared with in-house and public databases.

RESULTS

The five infants with CGL displayed generalized lipodystrophy, skeletal muscle hypertrophy, hepatomegaly, hypertriglyceridemia, hyperinsulinemia, and liver dysfunction. Four patients (#2-5) showed more severe hypertriglyceridemia than Patient #1. A compound heterozygosity for novel frameshift mutations c.622_626delTCCTC and c.513delC in AGPAT2 was identified in Patient #1. Seven mutations in BSCL2 were found among Patients #2-5, in which splice site mutation c.404+1G > T, nonsense mutation c.402C > G, and frameshift mutation c.759_760delGA were novel. After medical treatment, metabolic parameters for all patients were under control. At the time of writing, they are seven to seventeen months old with much improved physical and cognitive development.

CONCLUSIONS

Two novel mutations in AGPAT2 and three novel mutations in BSCL2 were identified from five unrelated infant patients diagnosed with CGL1 and CGL2.

A Single Complex Agpat2 Allele in a Patient With Partial Lipodystrophy

Genetic lipodystrophies are a group of rare syndromes associated with major metabolic complications – including severe insulin resistance, type 2 diabetes mellitus, and hypertriglyceridemia – which are classified according to the distribution of adipose tissue. Lipodystrophies can be present at birth or develop during life and can range from local to partial and general. With at least 18 different genes implicated so far, definite diagnosis can be challenging due to clinical and genetic heterogeneity. In an adult female patient with clinical and metabolic features of partial lipodystrophy we identified via whole genome sequencing (WGS) a single complex AGPAT2 allele [V67M;V167A], functionally equivalent to heterozygosity. AGPAT2 encodes for an acyltransferase implicated in the biosynthesis of triacylglycerol and glycerophospholipids. So far homozygous and compound heterozygous mutations in AGPAT2 have only been associated with generalized lipodystrophy. A SNP risk score analysis indicated that the index patient is not predisposed to lipodystrophy based on her genetic background. The partial phenotype in our patient is therefore more likely associated to the genetic variants in AGPAT2. To test whether the resulting double-mutant AGPAT2 protein is functional we analyzed its in vitro enzymatic activity via mass spectrometry. The resulting AGPAT2 double mutant is enzymatically inactive. Our data support the view that the current classification of lipodystrophies as strictly local, partial or generalized may have to be re-evaluated and viewed more as a continuum, both in terms of clinical presentation and underlying genetic causes. Better molecular understanding of lipodystrophies may lead to new therapies to treat adipose tissue dysfunction in common and rare diseases.

Performance Measurement and Comparative Transcriptome Analysis Revealed the Efforts on Hybrid Improvement of Qinchuan Cattle

Crossbreeding can provide productive gains through heterosis, however, surveys about the effects of crossbreeding through global transcriptomic sequencing are few. This study revealed that Angus × Qinchuan cattle (AQF) have improved performance characteristics compared to Qinchuan cattle (QCF). We performed RNA-seq on the subcutaneous fat tissue of QCF and AQF. More than 42.2 million clean reads were obtained in each sample. We detected 40 and 21 breed-specific highly expressed genes (FPKM > 500) in QCF and AQF, respectively. Furthermore, a total of 353 differentially expressed genes (DEGs, |log2 ratio| ≥ 1 and Probability ≥ 0.8) were found between these two groups, of which 227 genes were upregulated in AQF and 126 genes were upregulated in QCF. Functional enrichment analyses showed that breed-specific highly expressed genes and DEGs were closely related to terms such as development in AQF, and adaption or immune in QCF. In addition, we also identified the novel transcript units, alternative splicing events, single-nucleotide polymorphisms and Indels. Our results revealed differences in inherent characteristics and genetic differences when comparing QCF with AQF.

Clinical Features and Management of Non-HIV-Related Lipodystrophy in Children: A Systematic Review

CONTEXT

Lipodystrophy syndromes are characterized by generalized or partial absence of adipose tissue.

OBJECTIVE

We conducted a systematic review to synthesize data on clinical and metabolic features of lipodystrophy (age at onset, < 18 years).

DATA SOURCE

Sources included Medline, Embase, Cochrane Library, Scopus and Non-Indexed Citations from inception through January 2016.

STUDY SELECTION

Search terms included lipodystrophy, and age 0 to 18 years. Patients with unambiguous diagnosis of lipodystrophy were included. Lipodystrophy secondary to HIV treatment was excluded.

DATA SYNTHESIS

We identified 1141 patients from 351 studies. Generalized fat loss involving face, neck, abdomen, thorax, and upper and lower limbs was explicitly reported in 65% to 93% of patients with congenital generalized lipodystrophy (CGL) and acquired generalized lipodystrophy (AGL). In familial partial lipodystrophy (FPL), fat loss occurred from upper and lower limbs, with sparing of face and neck. In acquired partial lipodystrophy (APL), upper limbs were involved while lower limbs were spared. Other features were prominent musculature, acromegaloid, acanthosis nigricans and hepatosplenomegaly. Diabetes mellitus was diagnosed in 48% (n = 222) of patients with CGL (mean age at onset, 5.3 years). Hypertriglyceridemia was observed in CGL, AGL and FPL. Multiple interventions were used, with most patients receiving ≥ 3 interventions and being ≥ 18 years of age at the initiation of interventions.

CONCLUSIONS

To our knowledge, this is the largest reported pooled database describing lipodystrophy patients with age at onset < 18 years. We have suggested core and supportive clinical features and summarized data on available interventions, outcomes and mortality.

Natural History of Congenital Generalized Lipodystrophy: A Nationwide Study From Turkey

CONTEXT

Congenital generalized lipodystrophy (CGL) is a rare autosomal recessive disorder characterized by near-total lack of body fat.

OBJECTIVE

We aimed to study natural history and disease burden of various subtypes of CGL.

DESIGN

We attempted to ascertain nearly all patients with CGL in Turkey.

SETTING

This was a nationwide study.

PATIENTS OR OTHER PARTICIPANTS

Participants included 33 patients (22 families) with CGL and 30 healthy controls.

MAIN OUTCOME MEASURE(S)

We wanted to ascertain genotypes by sequencing of the known genes. Whole-body magnetic resonance imaging was used to investigate the extent of fat loss. Metabolic abnormalities and end-organ complications were measured on prospective follow-up.

RESULTS

Analysis of the AGPAT2 gene revealed four previously reported and four novel mutations (CGL1; c.144C>A, c.667_705delinsCTGCG, c.268delC, and c.316+1G>T). Analysis of the BSCL2 gene revealed four different homozygous and one compound heterozygous possible disease-causing mutations (CGL2), including four novel mutations (c.280C>T, c.631delG, c.62A>T, and c.465-468delGACT). Two homozygous PTRF mutations (c.481-482insGTGA and c.259C>T) were identified (CGL4). Patients with CGL1 had preservation of adipose tissue in the palms, soles, scalp, and orbital region, and had relatively lower serum adiponectin levels as compared to CGL2 patients. CGL4 patients had myopathy and other distinct clinical features. All patients developed various metabolic abnormalities associated with insulin resistance. Hepatic involvement was more severe in CGL2. End-organ complications were observed at young ages. Two patients died at age 62 years from cardiovascular events.

CONCLUSIONS

CGL patients from Turkey had both previously reported and novel mutations of the AGPAT2, BSCL2, and PTRF genes. Our study highlights the early onset of severe metabolic abnormalities and increased risk of end-organ complications in patients with CGL.

Berardinelli-Seip Syndrome - A Case Report

Congenital generalized lipodystrophy (CGL), also known as Berardinelli-Seip syndrome (BSS), is a rare autosomal recessive disease characterized by near total absence of adipose tissue and muscular hypertrophy. Additional common clinical signs are acanthosis nigricans, acromegaloid features, hepatomegaly, hyperandrogenism, altered glucose intolerance, cardiomyopathy and hypertriglyceridemia. An 11-year-old girl was admitted to our Clinic presenting with hyperandrogenic features, generalized lack of adipose tissue, generalized muscular hypertrophy and brownish colored skin on the neck, axillas and inguinal folds associated with impaired glucose tolerance and hypertension. A clinical diagnosis of congenital generalized lipodystrophy was made.

Barraquer-Simons syndrome: a rare form of acquired lipodystrophy

Background

Human lipodystrophies are uncommon disorders, with important clinical consequences, which are often undiagnosed. The Barraquer–Simons syndrome is a form of partial symmetric lipodystrophy of unknown etiology, characterized by the loss of subcutaneous adipose tissue, limited to upper part of the body. Insulin resistance and metabolic complications are less common than with other lipodystrophy subtypes. Patients usually have decreased serum complement-component 3 levels, associated with complement activation by the alternative pathway, which may indicate the presence of renal involvement.

Case presentation

The authors report a case of a 31-year-old woman with progressive loss of subcutaneous fat, limited to the face, neck and thorax. She presented no severe metabolic complications, neither signs of insulin resistance. Laboratory tests revealed mild dyslipidemia, and low serum levels of complement-component 3. Clinical and biochemical characteristics were consistent with the diagnosis of Barraquer–Simons syndrome.

Conclusion

The present case illustrates the importance of recognizing the clinical features of this lipodystrophic syndrome, which may present potentially severe consequences and psychological distress. A brief overview is made, addressing the clinical signs of the disease, its course, and how to manage it.

Congenital generalized lipodystrophies--new insights into metabolic dysfunction

Congenital generalized lipodystrophy (CGL) is a heterogeneous autosomal recessive disorder characterized by a near complete lack of adipose tissue from birth and, later in life, the development of metabolic complications, such as diabetes mellitus, hypertriglyceridaemia and hepatic steatosis. Four distinct subtypes of CGL exist: type 1 is associated with AGPAT2 mutations; type 2 is associated with BSCL2 mutations; type 3 is associated with CAV1 mutations; and type 4 is associated with PTRF mutations. The products of these genes have crucial roles in phospholipid and triglyceride synthesis, as well as in the formation of lipid droplets and caveolae within adipocytes. The predominant cause of metabolic complications in CGL is excess triglyceride accumulation in the liver and skeletal muscle owing to the inability to store triglycerides in adipose tissue. Profound hypoleptinaemia further exacerbates metabolic derangements by inducing a voracious appetite. Patients require psychological support, a low-fat diet, increased physical activity and cosmetic surgery. Aside from conventional therapy for hyperlipidaemia and diabetes mellitus, metreleptin replacement therapy can dramatically improve metabolic complications in patients with CGL. In this Review, we discuss the molecular genetic basis of CGL, the pathogenesis of the disease's metabolic complications and therapeutic options for patients with CGL.

Congenital generalized lipodystrophy: identification of novel variants and expansion of clinical spectrum

Congenital generalized lipodystrophy (CGL) is an autosomal recessive disorder with two major subtypes. Variants in AGPAT2 result in CGL type 1 with milder manifestations, whereas BSCL2 variants cause CGL type 2 with more severe features. Muscle hypertrophy caused by lack of adipose tissue is present early in life in CGL patients. Our aim was to investigate 10 CGL patients from 7 different countries and report genotype-phenotype relationships. Genetic analysis identified disease-causing variants in AGPAT2 (five patients) and in BSCL2 (five patients), including three novel variants; c.134C>A (p.Ser45*), c.216C>G (p.Tyr72*) in AGPAT2 and c.458C>A (p.Ser153*) in BSCL2. We also report possible novel clinical features such as anemia, breast enlargement, steatorrhea, intraventricular hemorrhage and nephrolithiasis in CGL patients. Generalized lipodystrophy and muscular hypertrophy were the only features in all of our patients. Hepatomegaly was the second common feature. Some manifestations were exclusively noticed in our CGL2 patients; hypertrichosis, high-pitched voice and umbilical hernia. Bone cysts and history of seizures were noticed only in CGL1 patients. The findings of this study expand our knowledge of genotype-phenotype correlations in CGL patients. These results have important clinical applications in diagnosis and management of the CGL patients as well as in genetic counseling in families at-risk.

Congenital lipodystrophies and dyslipidemias

Lipodystrophies are rare acquired and genetic disorders characterized by the selective loss of adipose tissue. One key metabolic feature of patients with congenital inherited lipodystrophy is hypertriglyceridemia. The precise mechanisms by which the lack of adipose tissue causes dyslipidemia remain largely unknown. In recent years, new insights have arisen from data obtained in vitro in adipocytes, yeast, drosophila, and very recently in several genetically modified mouse models of generalized lipodystrophy. A common metabolic pathway involving accelerated lipolysis and defective energy storage seems to contribute to the dyslipidemia associated with congenital generalized lipodystrophy syndromes, although the pathophysiological changes may vary with the nature of the mutation involved. Therapeutic management of dyslipidemia in patients with lipodystrophy is primarily based on specific approaches using recombinant leptin therapy. Preclinical studies suggest a potential efficacy of thiazolidinediones that remains to be assessed in dedicated clinical trials.

Berardinelli-Seip syndrome and achalasia: a shared pathomechanism?

Berardinelli-Seip congenital lipodystrophy (BSCL) is an uncommon autosomal recessive disorder. Patients with BSCL present with a distinct phenotype since subcutaneous fat is largely lacking and musculature has become more prominent. During childhood, diabetes and acanthosis nigricans evolve and female patients may develop hirsutism. Different genes encoding this entity have been described. Achalasia is a rare esophageal motility disorder, characterized by its distinct motility pattern with absent or incomplete lower esophageal sphincter (LES) relaxations. The exact cause of achalasia is yet unknown. Here, we describe a patient with achalasia in the context of BSCL, which might be linked by a shared pathophysiologic background, as evaluated in this case report.

CONCLUSION

In a BSCL patient presenting with gastrointestinal symptoms, a motility disorder of the gastrointestinal tract should be considered.

WHAT IS KNOWN

• Berardinelli-Seip congenital lipodystrophy (BSCL) and achalasia are both disorders characterized by low prevalence. What is New: • Co-existence of both diseases is described in this report. Linkage by a potential common pathophysiologic background is discussed in this paper.

Towards a mechanistic understanding of lipodystrophy and seipin functions

CGL (Congenital generalized lipodystrophy) is a genetic disorder characterized by near complete loss of adipose tissue along with increased ectopic fat storage in other organs including liver and muscle. Of the four CGL types, BSCL2 (Berardinelli-Seip Congenital lipodystrophy type 2), resulting from mutations in the BSCL2/seipin gene, exhibits the most severe lipodystrophic phenotype with loss of both metabolic and mechanical adipose depots. The majority of Seipin mutations cause C-terminal truncations, along with a handful of point mutations. Seipin localizes to the ER and is composed of a conserved region including a luminal loop and two transmembrane domains, plus cytosolic N- and C-termini. Animal models deficient in seipin recapitulate the human lipodystrophic phenotype. Cells isolated from seipin knockout mouse models also exhibit impaired adipogenesis. Mechanistically, seipin appears to function as a scaffolding protein to bring together interacting partners essential for lipid metabolism and LD (lipid droplet) formation during adipocyte development. Moreover, cell line and genetic studies indicate that seipin functions in a cell-autonomous manner. Here we will provide a brief overview of the genetic association of the CGLs, and focus on the current understanding of differential contributions of distinct seipin domains to lipid storage and adipogenesis. We will also discuss the roles of seipin-interacting partners, including lipin 1 and 14-3-3β, in mediating seipin-dependent regulation of cellular pathways such as actin cytoskeletal remodelling.

What's the matter with MAT? Marrow adipose tissue, metabolism, and skeletal health

Marrow adipose tissue (MAT) is functionally distinct from both white and brown adipose tissue and can contribute to systemic and skeletal metabolism. MAT formation is a spatially and temporally defined developmental event, suggesting that MAT is an organ that serves important functions and, like other organs, can undergo pathologic change. The well-documented inverse relationship between MAT and bone mineral density has been interpreted to mean that MAT removal is a possible therapeutic target for osteoporosis. However, the bone and metabolic phenotypes of patients with lipodystrophy argues that retention of MAT may actually be beneficial in some circumstances. Furthermore, MAT may exist in two forms, regulated and constitutive, with divergent responses to hematopoietic and nutritional demands. In this review, we discuss the role of MAT in lipodystrophy, bone loss, and metabolism, and highlight our current understanding of this unique adipose tissue depot.

Divergent metabolic phenotype between two sisters with congenital generalized lipodystrophy due to double AGPAT2 homozygous mutations. a clinical, genetic and in silico study

Congenital generalized lipodystrophy (CGL) is a rare autosomal recessive disorder characterized by extreme reduction of white adipose tissue (WAT) mass. CGL type 1 is the most frequent form and is caused by mutations in AGPAT2. Genetic and clinical studies were performed in two affected sisters of a Chilean family. These patients have notoriously dissimilar metabolic abnormalities that correlate with differential levels of circulating leptin and soluble leptin receptor fraction. Sequencing of AGPAT2 exons and exon-intron boundaries revealed two homozygous mutations in both sisters. Missense mutation c.299G>A changes a conserved serine in the acyltransferase NHX4D motif of AGPAT2 (p.Ser100Asn). Intronic c.493-1G>C mutation destroy a conserved splicing site that likely leads to exon 4 skipping and deletion of whole AGPAT2 substrate binding domain. In silico protein modeling provided insights of the mechanisms of lack of catalytic activity owing to both mutations.

Exploring the pathophysiology behind the more common genetic and acquired lipodystrophies

Lipodystrophies are an immense group of genetic or acquired metabolic disorders that are characterized by varying degrees of body fat loss and in some instances localized accumulation of subcutaneous fat. Lipodystrophies are often tightly linked with profound metabolic complications; this strong bond emphasizes and reinforces the significance of adipose tissue as a dynamic endocrine organ. The extent of fat loss determines the severity of associated metabolic complications such as diabetes mellitus, hypertriglyceridemia and hepatic steatosis. The lipodystrophies can be divided into generalized, partial or local, depending on the degree and locality of the observable fat loss; moreover, the generalized and partial divisions can be partitioned further into inherited or acquired forms. The major genetic factors in the generalized forms of the lipodystrophies, particularly Congenital generalized lipodystrophy (CGL)-Berardinelli-Seip syndrome, are the AGPAT2, BSCL2, caveolin 1 (CAV1) and polymerase-I-and-transcriptrelease factor (PTRF) genes. In the acquired forms, genes such as LMNA, PPARG, CIDEC (cell-death-inducing DNA fragmentation factor a-like effector c) and PLIN1 are heavily involved in familial partial lipodystrophy (FPLD) type 2 (also known as the Dunnigan-Variety) and WRN along with RECQL5 in Werner Syndrome (WS). Autoimmune causes are particularly noted in acquired partial lipodystrophy (APL)-Barraquer-Simons syndrome and in AGL-Lawrence syndrome; panniculitis has been shown to have a substantial role in the former as well as in other forms of localized lipodystrophies. Patients with human immunodeficiency virus (HIV) exposed to protease inhibitors, nucleoside reverse transcriptase inhibitors (NRTIs) (for example, zidovudine and stavudine) or non-nucleoside reverse transcriptase inhibitors (NNRTIs) (for example, efavirenz) while undergoing Highly Active Antiretroviral Therapy (HAART) have led to the current most-prevalent form of the lipodystrophies: lipodystrophy in HIV-infected patients (LD-HIV) and HAART-associated lipodystrophy syndrome (HALS).

Identification of a novel nonsense mutation and a missense substitution in the AGPAT2 gene causing congenital generalized lipodystrophy type 1

Congenital generalized lipodystrophy (CGL) is an autosomal recessive disease characterized by the generalized scant of adipose tissue. CGL type 1 is caused by mutations in gene encoding 1-acylglycerol-3-phosphate O-acyltransferase-2 (AGPAT2). A clinical and molecular genetic investigation was performed in affected and unaffected members of two families with CGL type 1. The AGPAT2 coding region was sequenced in index cases of the two families. The presence of the identified mutations in relevant parents was tested. We identified a novel nonsense mutation (c.685G>T, p.Glu229*) and a missense substitution (c.514G>A, p.Glu172Lys). The unaffected parents in both families were heterozygous carrier of the relevant mutation. The results expand genotype-phenotype spectrum in CGL1 and will have applications in prenatal and early diagnosis of the disease. This is the first report of Persian families identified with AGPAT2 mutations.

Clinical review#: Lipodystrophies: genetic and acquired body fat disorders

CONTEXT

Lipodystrophies are heterogeneous, genetic or acquired disorders characterized by selective loss of body fat and predisposition to insulin resistance. The extent of fat loss determines the severity of associated metabolic complications such as diabetes mellitus, hypertriglyceridemia, and hepatic steatosis.

EVIDENCE ACQUISITION AND SYNTHESIS

Both original and review articles were found via PubMed search reporting on clinical features and management of various types of lipodystrophies and were integrated with the author's knowledge of the field.

CONCLUSION

The autosomal recessive congenital generalized lipodystrophy and autosomal dominant familial partial lipodystrophy (FPL) are the two most common types of genetic lipodystrophies. Mutations in AGPAT2, BSCL2, CAV1, and PTRF have been reported in congenital generalized lipodystrophy and in LMNA, PPARG, AKT2, and PLIN1 in FPL. CIDEC is the disease gene for autosomal recessive, FPL and LMNA and ZMPSTE24 for autosomal recessive, mandibuloacral dysplasia-associated lipodystrophy. Recently, an autosomal recessive autoinflammatory lipodystrophy syndrome was reported to be due to PSMB8 mutation. Molecular genetic bases of many rare forms of genetic lipodystrophies remain to be elucidated. The most prevalent subtype of acquired lipodystrophy currently occurs with prolonged duration of protease inhibitor-containing, highly-active antiretroviral therapy in HIV-infected patients. The acquired generalized and partial lipodystrophies are mainly autoimmune in origin and display complement abnormalities. Localized lipodystrophies occur due to drug or vaccine injections, pressure, panniculitis, and other unknown reasons. The current management includes cosmetic surgery and early identification and treatment of metabolic and other complications with diet, exercise, hypoglycemic drugs, and lipid-lowering agents.

[Genetic and metabolic description of five patients with Berardinelli-Seip syndrome]

OBJECTIVE

To report the genetic and metabolic profile of patients with Berardinelli-Seip syndrome (BSCL) followed at Instituto da Criança, HC-FMUSP.

SUBJECTS AND METHODS

Patients with clinical features of BSCL (n = 5), all female, were evaluated through serum levels of glucose, insulin, lipids, leptin, and liver enzymes. Abdominal sonography and DNA analysis were also performed.

RESULTS

Leptin deficiency and hypertriglyceridemia were found in all the patients. Three progressed to diabetes mellitus. Four patients have mutations in AGPAT2 gene and one have a mutation in CAV1 gene.

CONCLUSION

The earliest metabolic abnormalities were hypertriglyceridemia and insulin resistance, culminating in the onset of diabetes at the time of puberty. Mutations in the AGPAT2 gene were the most frequent in our patients.

Description of an AGPAT2 pathologic allelic variant in a 54-year-old Caucasian woman with Berardinelli-Seip syndrome

A 54-year-old Italian female patient was admitted to our Department with the diagnosis of type 2 diabetes poorly controlled with insulin therapy. The patient was born by consanguineous parents (first degree cousins); she had acromegaloid features, diffuse lipoatrophy and muscular pseudo-hypertrophy since childhood. To confirm the clinical hypothesis of congenital generalized lipodystrophy (CGL) or Berardinelli-Seip syndrome, the sequences of AGPAT2 (encoding for 1-acyl-sn-glycerol-3-phosphate acyltransferase beta) and BSCL2 (encoding for seipin) candidate genes were analyzed. DNA analysis showed the presence of a homozygous mutation in exon 3 of the AGPAT2 gene (P112L). This is the first description of a Caucasian subject with CGL who carries the pathologic allelic variant P112L of the AGPAT2 gene.

A Taiwanese boy with congenital generalized lipodystrophy caused by homozygous Ile262fs mutation in the BSCL2 gene

Congenital generalized lipodystrophy (CGL) is a rare autosomal recessive disease that is characterized by a near-complete absence of adipose tissue from birth or early infancy. Mutations in the BSCL2 gene are known to result in CGL2, a more severe phenotype than CGL1, with earlier onset, more extensive fat loss and biochemical changes, more severe intellectual impairment, and more severe cardiomyopathy. We report a 3-month-old Taiwanese boy with initial presentation of a lack of subcutaneous fat, prominent musculature, generalized eruptive xanthomas, and extreme hypertriglyceridemia. Absence of mechanical adipose tissue in the orbits and scalp was revealed by head magnetic resonance imaging. Hepatomegaly was noticed, and histological examination of a liver biopsy specimen suggested severe hepatic steatosis and periportal necrosis. However, echocardiography indicated no sign of cardiomyopathy and he showed no distinct intellectual impairment that interfered with daily life. About 1 year later, abdominal computed tomography revealed enlargement of kidneys. He had a homozygous insertion of a nucleotide, 783insG (Ile262fs mutation), in exon 7 of the BSCL2 gene. We reviewed the genotype of CGL cases from Japan, India, China and Taiwan, and found that BSCL2 is a major causative gene for CGL in Asian.

Pathology of congenital generalized lipodystrophy in Agpat2-/- mice

Congenital generalized lipodystrophy (CGL) comprises a heterogeneous group of rare diseases associated with partial or total loss of adipose tissue. Of these, autosomal recessive Berardinelli-Seip congenital lipodystrophy (BSCL) is characterized by the absence of metabolically active subcutaneous and visceral adipose tissues. Metabolic abnormalities associated with lipodystrophy include insulin resistance, hypertriglyceridemia, hepatic steatosis, and diabetes. One form of BSCL has been linked to genetic mutations affecting the lipid biosynthetic enzyme 1-acyl-sn-glycerol 3-phosphate O-acyltransferase 2 (AGPAT2), which is highly expressed in adipose tissue. Precisely how AGPAT2 deficiency causes lipodystrophy remains unresolved, but possible mechanisms include impaired lipogenesis (triglyceride synthesis and storage), blocked adipogenesis (differentiation of preadipocytes to adipocytes), or apoptosis/necrosis of adipocytes. Agpat2(-/-) mice share important pathophysiologic features of CGL previously reported in humans. However, the small white adipose tissue (WAT) depots consisting largely of amoeboid adipocytes with microvesiculated basophilic cytoplasm showed that adipogenesis with deficient lipogenesis was present in all usual locations. Although well-defined lobules of brown adipose tissue (BAT) were present, massive necrosis resulted in early ablation of BAT. Although necrotic or apoptotic adipocytes were not detected in WAT of 10-day-old Agpat2(-/-), the absence of adipocytes in aged mice indicates that these cells must undergo necrosis/apoptosis at some point. Another significant finding in aged lipodystrophic mice was massive pancreatic islet hypertrophy in the face of chronic hyperglycemia, which suggests that glucotoxicity is insufficient by itself to cause β-cell loss and that adipocyte-derived factors help regulate total β-cell mass.

Higher adiponectin levels in patients with Berardinelli-Seip congenital lipodystrophy due to seipin as compared with 1-acylglycerol-3-phosphate-o-acyltransferase-2 deficiency

CONTEXT

Human lipodystrophies are characterized by loss of adipose tissue, insulin resistance, and metabolic complications. The mechanisms linking fat loss to severe insulin resistance remain unclear. Adipokines may have important roles as intermediary players in metabolism.

OBJECTIVE

We sought to determine the plasma concentrations of leptin and adiponectin in patients with Berardinelli-Seip congenital lipodystrophy (BSCL) harboring mutations in the genes encoding either 1-acylglycerol-3-phosphate-O-acyltransferase-2 (AGPAT2) or BSCL2/seipin, in comparison with patients with other forms of inherited or acquired lipodystrophies or insulin receptor alterations.

DESIGN

Leptin and total and high-molecular-weight adiponectin were measured in plasma of 16 BSCL1/AGPAT2 and 19 BSCL2/seipin patients and compared with heterozygous (n = 22) or nonmutated relatives (controls, n = 30); patients with Dunnigan-type partial lipodystrophy due to lamin A/C mutations (n = 23), HIV-related lipodystrophy (n = 124), and insulin receptor dysfunctions caused by mutations or autoantibodies (n = 17).

RESULTS

Leptin was dramatically decreased in BSCL patients as compared with other subgroups. Adiponectin was decreased in BSCL as compared with controls and patients with altered insulin receptor but was discrepant between the two BSCL subgroups. Whereas total and high-molecular-weight adiponectin levels were almost undetectable in BSCL1/AGPAT2 patients, higher levels were detected in BSCL2/seipin patients, comparable with those of patients with partial lipodystrophy. Adiponectin greater than 1.6 mg/liter had a 100% negative predictive value for AGPAT2 mutations in inherited lipodystrophies.

CONCLUSIONS

The presence of circulating adiponectin in BSCL2/seipin patients with near absence of adipose tissue outlines the complexity of adiponectin biology. Use of circulating adiponectin might be helpful to guide the genetic investigations in BSCL.

Novel mutations of the BSCL2 and AGPAT2 genes in 10 families with Berardinelli-Seip congenital generalized lipodystrophy syndrome

CONTEXT

Congenital generalized lipodystrophy, or Berardinelli-Seip syndrome, is a rare autosomal recessive disease caused by mutations in either the BSCL2 or AGPAT2 genes. This syndrome is characterized by an almost complete loss of adipose tissue usually diagnosed at birth or early infancy resulting in apparent muscle hypertrophy. Common clinical features are acanthosis nigricans, hepatomegaly with or without splenomegaly and high stature. Acromegaloid features, cardiomyopathy and mental retardation can also be present.

DESIGN

We investigated 11 kindreds from different geographical areas of Brazil (northeast and southeast). All coding regions as well as flanking intronic regions of both genes were examined. Polymerase chain reaction (PCR) amplifications were performed using primers described previously and PCR products were sequenced directly.

RESULTS

Four AGPAT2 and two BSCL2 families harboured the same set of mutations. BSCL2 gene mutations were found in the homozygous form in four kindreds (c.412C>T c.464T>C, c.518-519insA, IVS5-2A>G), and in two kindreds compound mutations were found (c.1363C>T, c.424A>G). In the other four families, one mutation of the AGPAT2 gene was found (IVS3-1G>C and c.299G>A).

CONCLUSIONS

We have demonstrated four novel mutations of the BSCL2 and AGPAT2 genes responsible for Berardinelli-Seip syndrome and Brunzell syndrome (AGPAT2-related syndrome).

The human lipodystrophy gene product Berardinelli-Seip congenital lipodystrophy 2/seipin plays a key role in adipocyte differentiation

Mutations in the Berardinelli-Seip congenital lipodystrophy 2 gene (BSCL2) are the underlying defect in patients with congenital generalized lipodystrophy type 2. BSCL2 encodes a protein called seipin, whose function is largely unknown. In this study, we investigated the role of Bscl2 in the regulation of adipocyte differentiation. Bscl2 mRNA is highly up-regulated during standard hormone-induced adipogenesis in 3T3-L1 cells in vitro. However, this up-regulation does not occur during mesenchymal stem cell (C3H10T1/2 cells) commitment to the preadipocyte lineage. Knockdown of Bscl2 by short hairpin RNA in C3H10T1/2 cells has no effect on bone morphogenetic protein-4-induced preadipocyte commitment. However, knockdown in 3T3-L1 cells prevents adipogenesis induced by a standard hormone cocktail, but adipogenesis can be rescued by the addition of peroxisome proliferator-activated receptor-gamma agonist pioglitazone at an early stage of differentiation. Interestingly, pioglitazone-induced differentiation in the absence of standard hormone is not associated with up-regulated Bscl2 expression. On the other hand, short hairpin RNA-knockdown of Bscl2 largely blocks pioglitazone-induced adipose differentiation. These experiments suggest that Bscl2 may be essential for normal adipogenesis; it works upstream or at the level of peroxisome proliferator-activated receptor-gamma, enabling the latter to exert its full activity during adipogenesis. Loss of Bscl2 function thus interferes with the normal transcriptional cascade of adipogenesis during fat cell differentiation, resulting in near total loss of fat or lipodystrophy.

Lipodystrophies: disorders of adipose tissue biology

The adipocytes synthesize and store triglycerides as lipid droplets surrounded by various proteins and phospholipids at its surface. Recently, the molecular basis of some of the genetic syndromes of lipodystrophies has been elucidated and some of these genetic loci have been found to contribute to lipid droplet formation in adipocytes. The two main types of genetic lipodystrophies are congenital generalized lipodystrophy (CGL) and familial partial lipodystrophy (FPL). So far, three CGL loci: 1-acylglycerol-3-phosphate-O-acyltransferase 2 (AGPAT2), Berardinelli-Seip Congenital Lipodystrophy 2 (BSCL2) and caveolin 1 (CAV1) and four FPL loci: lamin A/C (LMNA), peroxisome proliferator-activated receptor gamma (PPARG), v-AKT murine thymoma oncogene homolog 2 (AKT2) and zinc metalloprotease (ZMPSTE24), have been identified. AGPAT2 plays a critical role in the synthesis of glycerophospholipids and triglycerides required for lipid droplet formation. Another protein, seipin (encoded by BSCL2 gene), has been found to induce lipid droplet fusion. CAV1 is an integral component of caveolae and might contribute towards lipid droplet formation. PPARgamma and AKT2 play important role in adipogenesis and lipid synthesis. In this review, we discuss and speculate about the contribution of various lipodystrophy genes and their products in the lipid droplet formation.

Fat poetry: a kingdom for PPAR gamma

Adipose tissue is not an inert cell mass contributing only to the storage of fat, but a sophisticated ensemble of cellular components with highly specialized and complex functions. In addition to managing the most important energy reserve of the body, it secretes a multitude of soluble proteins called adipokines, which have beneficial or, alternatively, deleterious effects on the homeostasis of the whole body. The expression of these adipokines is an integrated response to various signals received from many organs, which depends heavily on the integrity and physiological status of the adipose tissue. One of the main regulators of gene expression in fat is the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma), which is a fatty acid- and eicosanoid-dependent nuclear receptor that plays key roles in the development and maintenance of the adipose tissue. Furthermore, synthetic PPARgamma agonists are therapeutic agents used in the treatment of type 2 diabetes.This review discusses recent knowledge on the link between fat physiology and metabolic diseases, and the roles of PPARgamma in this interplay via the regulation of lipid and glucose metabolism. Finally, we assess the putative benefits of targeting this nuclear receptor with still-to-be-identified highly selective PPARgamma modulators.

Genetic disorders of adipose tissue development, differentiation, and death

Lack of adipose tissue, either complete or partial, is the hallmark of disorders known as lipodystrophies. Patients with lipodystrophies suffer from metabolic complications similar to those associated with obesity, including insulin resistance, type 2 diabetes, hypertriglyceridemia, and hepatic steatosis. The loss of body fat in inherited lipodystrophies can be caused by defects in the development and/or differentiation of adipose tissue as a consequence of mutations in a number of genes, including PPARG (encoding a nuclear hormone receptor), AGPAT2 (encoding an enzyme involved in the biosynthesis of triglyceride and phospholipids), AKT2 (encoding a protein involved in insulin signal transduction), and BSCL2 (encoding seipin, whose role in the adipocyte biology remains unclear). The loss of body fat can also be caused by the premature death of adipocytes due to mutations in lamin A/C, nuclear lamina proteins, and ZMPSTE24, which modifies the prelamin A post-translationally. In this review, we focus on the molecular basis of inherited lipodystrophies as they relate to adipocyte biology and their associated phenotypic manifestations.

Leptin therapy for partial lipodystrophy linked to a PPAR-gamma mutation

AIMS/HYPOTHESIS

Partial lipodystrophy (PL) is most commonly characterized by loss of subcutaneous fat in the extremities with preservation of truncal fat and is associated with insulin resistance, diabetes and hyperlipidaemia. Recombinant human leptin (r-metHuLeptin) therapy has been shown to be effective in treating metabolic abnormalities associated with congenital or acquired generalized lipodystrophy and PL associated with lamin A/C (LMNA) gene mutations or highly active antiretroviral therapy (HAART). Our aim was to assess the effectiveness of leptin therapy in treating metabolic complications of PL associated with heterozygous peroxisome proliferator activated receptor gamma (PPARG) mutations. This is the first report to detail the clinical response of a patient with PL due to a PPARG mutation treated with r-metHuLeptin.

METHODS

A 36-year-old female with PL associated with a heterozygous PPARG mutation complicated by poorly controlled diabetes and severe, refractory hypertriglyceridaemia was enrolled in a National Institutes of Health (NIH) protocol to evaluate the role of r-metHuLeptin in lipodystrophy. The patient received escalating doses of r-metHuLeptin until a dose 0.12 mg/kg/day was reached. Metabolic parameters, including serum chemistries, fasting blood glucose, glycated haemoglobin (HbA1c), lipid profile, an oral glucose tolerance test (OGTT), an insulin tolerance test (ITT), liver volume, percentage body fat and energy expenditure were followed at regular time intervals over 18 months of therapy.

RESULTS

Eighteen months of r-MetHuLeptin therapy was associated with a marked improvement in glucose homeostasis as evidenced by normalization of the fasting blood glucose (baseline = 8.3 mmol/l; 18 months = 4.9 mmol/l), lowering of HbA1c (baseline = 9.9%; 18 months = 7.2%) and improved tolerance to an oral glucose load. In addition, a striking amelioration in the patient's refractory, severe hypertriglyceridaemia was observed (baseline = 21.15 mmol/l; 18 months = 5.96 mmol/l).

CONCLUSION

r-MetHuLeptin is effective in treating metabolic complications associated with PL due to PPARG mutations. In the context of previously published work, our findings suggest that the response to r-MetHuLeptin is independent of the aetiology in lipodystrophy.

Sequential regulation of diacylglycerol acyltransferase 2 expression by CAAT/enhancer-binding protein beta (C/EBPbeta) and C/EBPalpha during adipogenesis

Diacylglycerol acyltransferase 2 (DGAT2) catalyzes the final step of triacylglycerol (TG) synthesis. Despite the existence of an alternative acyltransferase (DGAT1), mice lacking DGAT2 have a severe deficiency of TG in adipose tissue, indicating a nonredundant role for this enzyme in adipocyte TG synthesis. We have studied the regulation of DGAT2 expression during adipogenesis. In both isolated murine preadipocytes and 3T3-L1 cells the temporal pattern of DGAT2 expression closely mimicked that of genes whose expression is regulated by CAAT/enhancer-binding protein beta (C/EBPbeta). Inhibition of C/EBPbeta expression in differentiating preadipocytes reduced DGAT2 expression, and electrophoretic mobility shift assay and chromatin immunoprecipitation experiments identified a promoter element in the DGAT2 gene that is likely to mediate this effect. The importance of C/EBPbeta in adipocyte expression of DGAT2 was confirmed by the finding of reduced DGAT2 expression in the adipose tissue of C/EBPbeta-null animals. However, DGAT2 expression is maintained at high levels during the later stages of adipogenesis, when C/EBPbeta levels decline. We show that, at these later stages of differentiation, C/EBPalpha is capable of substituting for C/EBPbeta at the same promoter element. These observations provide novel insight into the transcriptional regulation of DGAT2 expression. Moreover, they further refine the complex and serial roles of the C/EBP family of transcription factors in inducing and maintaining the metabolic properties of mature adipocytes.

Founder effect of the 669insA mutation in BSCL2 gene causing Berardinelli-Seip congenital lipodystrophy in a cluster from Brazil

Congenital generalized lipodystrophy (CGL) or Berardinelli-Seip Syndrome (BSCL) is a rare autosomal recessive disease characterized by a nearly-complete absence of adipose tissue from birth and severe metabolic alterations. The 669insA mutation in exon 4 of the BSCL2 gene was identified as the major genetic alteration leading to BSCL in a group of 22 patients from the northeastern Brazilian state of Rio Grande do Norte. Aiming to investigate the causes of the high frequency of BSCL in this region, a molecular genetic study was conducted using eight microsatelite markers located in chromosome 11. Additional investigations concerning the proportion of expected homozygous and heterozygous individuals, genetic diversity, fixation index and coefficient of endogamy were undertaken, and indicated significant differences by comparing the allelic and haplotypic frequencies observed for the BSCL affected families and the control group. It was concluded that a founder effect, genetic drift and consanguineous marriages have significantly affected the structure of this population, resulting in the highest frequency of BSCL in Brazil.

Transcriptomic characterization of the long-term dihydrotestosterone effects in adipose tissue

OBJECTIVE

To study the long-term transcriptomic effects of dihydrotestosterone (DHT) in adipose tissue. Fat distribution is regulated by sexual hormones. It is still unclear if androgens are promoting or reducing intra-abdominal fat accumulation.

RESEARCH METHODS AND PROCEDURES

Retroperitoneal adipose tissue were isolated from each group of gonadectomized (GDX) C57BL6 male mice treated with vehicle or DHT for 21 days. Serial analysis of gene expression (SAGE) was performed to generate approximately 150,000 SAGE tags from each sample.

RESULTS

Among the numerous genes regulated by DHT, transcripts involved in glycolysis, such as aldolase 1 A isoform and pyruvate kinase muscle as well as lipogenic transcripts, such as malic enzyme supernatant and ELOVL family member 6 elongation of long chain fatty acids were down-regulated by androgen supplementation. In contrast, transcripts involved in lipolysis and fatty acid oxidation, such as carboxylesterase 3, acetyl-coenzyme A acyltransferase 1, 3-ketoacyl-CoA thiolase B and enoyl-coenzyme A hydratase/3-hydroxyacyl coenzyme A dehydrogenase were up-regulated by DHT. Pro-apoptotic transcripts such as cell death-inducing DFFA-like effector c, BCL2/adenovirus E1B 19 kDa-interacting protein 1 NIP3 and -interacting protein 3-like were up-regulated by DHT, whereas transcripts involved in promotion of cell cycle such as cyclin D2 were down-regulated by DHT.

DISCUSSION

These results suggest that chronic androgen treatment may help to improve metabolic profile by regulating various critical pathways involved in adipose tissue physiology. In addition, several genes associated with a healthier metabolic profile, such as adiponectin and CD36 antigen, were up-regulated by 21 days of DHT treatment.

[Primary lipodystrophies]

Primary lipodystrophies represent a heterogeneous group of very rare diseases with a prevalence of less than 1 case for 100.000, inherited or acquired, caracterized by a loss of body fat either generalized or localized (lipoatrophy). In some forms, lipoatrophy is associated with a selective hypertrophy of other fat depots. Clinical signs of insulin resistance are often present: acanthosis nigricans, signs of hyperandrogenism. All lipodystrophies are associated with dysmetabolic alterations with insulin resistance, altered glucose tolerance or diabetes and hypertriglyceridemia leading to a risk of acute pancreatitis. Chronic complications are those resulting from diabetes involving the retina, kidney and nerves, cardiovascular complications and steatotic liver lesions that could result in cirrhosis. Genetic forms of generalized lipodystrophy (or Berardinelli-Seip syndrome) result, in most cases, from recessive mutations in one of two genes: either BSCL2 coding seipin or BSCL1 coding AGPAT2, an acyl-transferase involved in triglyceride synthesis. Acquired generalized lipodystrophy (Lawrence syndrome) is of unknown origin but is sometimes associated with signs of autoimmunity. Partial lipodystrophies can be familial with dominant transmission. Heterozygous mutations have been identified in the LMNA gene encoding nuclear lamin A/C belonging to the nuclear lamina, or in PPARG encoding the adipogenic transcription factor PPARgamma. Some less typical lipodystrophies, associated with signs of premature aging, have been linked to mutations in LMNA or in the ZMPSTE24 gene encoding the protease responsible for the maturation of prelamin A into lamin A. Acquired partial lipodystrophy (Barraquer-Simons syndrome) is characterized by cephalothoracic fat loss. Its aetiology is unknown but mutations in LMNB2, encoding the lamina protein lamin B2, could represent susceptibility factors. Highly active antiretroviral treatments for HIV infection are currently the most frequent cause of acquired secondary lipodystrophic syndromes. The genetic diagnosis is performed in specialized laboratories and, in the most severe forms, antenatal diagnosis could be proposed. Treatment of diabetes, dyslipidemia and complications involves the classical intervention strategies. Insulino-sensitizing drugs are useful. Therapeutic trials with recombinant human leptin in patients with very low leptin levels reported good results with respect to the metabolic and liver alterations. The prognosis is linked to the precocity and severity of the diabetic, cardiovascular and liver complications.