(from OMIM) Albert et al. (2014) sequenced 12 lipolytic-pathway genes in 24 Old Order Amish individuals whose fasting serum triglyceride levels were at the extremes of the distribution, and detected a 19-bp deletion in the LIPE gene in an individual whose triglyceride level was at the upper extreme. Genotyping for the LIPE deletion in 2,738 participants in the Amish Complex Disease Research Program identified 1 individual who was homozygous for the deletion ('DD' genotype) and 140 heterozygotes. Homozygous individuals exhibited impaired lipolysis and showed evidence for redistribution of body fat as well as altered metabolic traits, including systemic insulin resistance and diabetes. Carriers of the deletion had an increased risk of metabolic dysfunction. In an Italian sister and brother from a consanguineous family with a late-onset form of partial lipodystrophy, originally reported by Carboni et al. (2014), Farhan et al. (2014) performed genomewide autozygosity mapping and whole-exome sequencing, and identified a frameshift mutation in the LIPE gene that segregated with disease in the family. Sollier et al. (2021) describe four novel mutations in three patients and model the disease using stem cells
AIMS: Hormone sensitive lipase (HSL), encoded by the LIPE gene, is involved in lipolysis. Based on prior animal and human studies, LIPE was analyzed as a candidate gene for the development of type 2 diabetes (T2D) in a community-based sample of American Indians. MATERIALS AND METHODS: Whole-exome sequence data from 6782 participants with longitudinal clinical measures were used to identify variation in LIPE. RESULTS: Among the 16 missense variants identified, an Arg611Cys variant (rs34052647; Cys-allele frequency =0.087) significantly associated with T2D (OR [95% CI]=1.38 [1.17-1.64], P =0.0002, adjusted for age, sex, birth year and the first 5 genetic principal components) and an earlier onset age of T2D (HR=1.22[1.09-1.36], P=0.0005). This variant was further analyzed for quantitative traits related to T2D. Among non-diabetic American Indians, those with the T2D risk Cys-allele had increased insulin levels during an oral glucose tolerance test (0.07 SD per Cys-allele, P=0.04) and a mixed meal test (0.08 log(10) microU/ml per Cys-allele, P=0.003), and had increased lipid oxidation rates post-absorptively and during insulin infusion (0.07 mg [kg estimated metabolic body size {EMBS}](-1) min(-1) per Cys-allele for both, P=0.01, 0.009 respectively) compared to individuals with the non-risk Arg-allele. In vitro functional studies showed that cells expressing the Cys-allele had a 17.2% decrease in lipolysis under isoproterenol stimulation (P = 0.03) and a 21.3% decrease in lipase enzyme activity measured by using P-Nitrophenyl Butyrate as substrate (P=0.04) compared to the Arg-allele. CONCLUSION: The Arg611Cys variant causes a modest impairment in lipolysis, thereby affecting glucose homeostasis and risk of T2D. This article is protected by copyright. All rights reserved.
Objective The term Multiple Symmetric Lipomatosis (MSL) describes a heterogeneous group of rare monogenic disorders and multifactorial conditions, characterized by upper-body adipose masses. Biallelic variants in LIPE encoding hormone sensitive lipase (HSL), a key lipolytic enzyme, were implicated in three families worldwide. We aimed to further delineate LIPE-related clinical features and pathophysiological determinants. Methods A gene panel was used to identify pathogenic variants. The disease features were reviewed at the French lipodystrophy reference center. The immunohistological, ultrastructural, and protein expression characteristics of lipomatous tissue were determined in surgical samples from one patient. The functional impact of variants was investigated by developing a model of adipose stem cells (ASCs) isolated from lipomatous tissue. Results We identified new biallelic LIPE null variants in three unrelated patients referred for MSL and/or partial lipodystrophy. The hallmarks of the disease, appearing in adulthood, included lower-limb lipoatrophy, upper-body and abdominal pseudolipomatous masses, diabetes and/or insulin resistance, hypertriglyceridemia, liver steatosis, high blood pressure, and neuromuscular manifestations. Ophthalmological investigations revealed numerous auto-fluorescent drusen-like retinal deposits in all patients. Lipomatous tissue and patient ASCs showed loss of HSL and decreased expression of adipogenic and mature adipocyte markers. LIPE-mutated ASCs displayed impaired adipocyte differentiation, decreased insulin response, defective lipolysis, and mitochondrial dysfunction. Conclusions Biallelic LIPE null variants result in a multisystemic disease requiring multidisciplinary care. Loss of HSL expression impairs adipocyte differentiation, consistent with the lipodystrophy/MSL phenotype and associated metabolic complications. Detailed ophthalmological examination could reveal retinal damage, further pointing to the nervous tissue as an important disease target.
Title: Homozygous LIPE mutation in siblings with multiple symmetric lipomatosis, partial lipodystrophy, and myopathy Zolotov S, Xing C, Mahamid R, Shalata A, Sheikh-Ahmad M, Garg A Ref: American Journal of Medicine Genet A, 173:190, 2017 : PubMed
Despite considerable progress in identifying causal genes for lipodystrophy syndromes, the molecular basis of some peculiar adipose tissue disorders remains obscure. In an Israeli-Arab pedigree with a novel autosomal recessive, multiple symmetric lipomatosis (MSL), partial lipodystrophy and myopathy, we conducted exome sequencing of two affected siblings to identify the disease-causing mutation. The 41-year-old female proband and her 36-year-old brother reported marked accumulation of subcutaneous fat in the face, neck, axillae, and trunk but loss of subcutaneous fat from the lower extremities and progressive distal symmetric myopathy during adulthood. They had increased serum creatine kinase levels, hypertriglyceridemia and low levels of high-density lipoprotein cholesterol. Exome sequencing identified a novel homozygous NC_000019.9:g.42906092C>A variant on chromosome 19, leading to a NM_005357.3:c.3103G>T nucleotide change in coding DNA and corresponding p.(Glu1035*) protein change in hormone sensitive lipase (LIPE) gene as the disease-causing variant. Sanger sequencing further confirmed the segregation of the mutation in the family. Hormone sensitive lipase is the predominant regulator of lipolysis from adipocytes, releasing free fatty acids from stored triglycerides. The homozygous null LIPE mutation could result in marked inhibition of lipolysis from some adipose tissue depots and thus may induce an extremely rare phenotype of MSL and partial lipodystrophy in adulthood associated with complications of insulin resistance, such as diabetes, hypertriglyceridemia and hepatic steatosis. (c) 2016 Wiley Periodicals, Inc.
BACKGROUND: Lipolysis regulates energy homeostasis through the hydrolysis of intracellular triglycerides and the release of fatty acids for use as energy substrates or lipid mediators in cellular processes. Genes encoding proteins that regulate energy homeostasis through lipolysis are thus likely to play an important role in determining susceptibility to metabolic disorders. METHODS: We sequenced 12 lipolytic-pathway genes in Old Order Amish participants whose fasting serum triglyceride levels were at the extremes of the distribution and identified a novel 19-bp frameshift deletion in exon 9 of LIPE, encoding hormone-sensitive lipase (HSL), a key enzyme for lipolysis. We genotyped the deletion in DNA from 2738 Amish participants and performed association analyses to determine the effects of the deletion on metabolic traits. We also obtained biopsy specimens of abdominal subcutaneous adipose tissue from 2 study participants who were homozygous for the deletion (DD genotype), 10 who were heterozygous (ID genotype), and 7 who were noncarriers (II genotype) for assessment of adipose histologic characteristics, lipolysis, enzyme activity, cytokine release, and messenger RNA (mRNA) and protein levels. RESULTS: Carriers of the mutation had dyslipidemia, hepatic steatosis, systemic insulin resistance, and diabetes. In adipose tissue from study participants with the DD genotype, the mutation resulted in the absence of HSL protein, small adipocytes, impaired lipolysis, insulin resistance, and inflammation. Transcription factors responsive to peroxisome-proliferator-activated receptor gamma (PPAR-gamma) and downstream target genes were down-regulated in adipose tissue from participants with the DD genotype, altering the regulation of pathways influencing adipogenesis, insulin sensitivity, and lipid metabolism. CONCLUSIONS: These findings indicate the physiological significance of HSL in adipocyte function and the regulation of systemic lipid and glucose homeostasis and underscore the severe metabolic consequences of impaired lipolysis. (Funded by the National Institutes of Health and others).
BACKGROUND: Familial lipodystrophies are rare inherited disorders associated with redistribution of body fat and development of dyslipidemia, insulin resistance, and diabetes. We previously reported 2 siblings with unusual late-onset familial partial lipodystrophy in whom heretofore known causative genes had been excluded. We hypothesized they had a mutation in a novel lipodystrophy gene. METHODS: Our approach centred on whole exome sequencing of the patients' DNA, together with genetic linkage analysis and a bioinformatic prioritization analysis. All candidate variants were assessed in silico and available family members were genotyped to assess segregation of mutations. RESULTS: Our prioritization algorithm led us to a novel homozygous nonsense variant, namely p.Ala507fsTer563 in the hormone sensitive lipase gene encoding, an enzyme that is differentially expressed in adipocytes and steroidogenic tissues. Pathogenicity of the mutation was supported in bioinformatic analyses and variant cosegregation within the family. CONCLUSIONS: We have identified a novel nonsense mutation in hormone sensitive lipase gene, which likely explains the lipodystrophy phenotype observed in these patients.
BACKGROUND: Although it has long been proposed that genetic factors contribute to adaptation to high altitude, such factors remain largely unverified. Recent advances in high-throughput sequencing have made it feasible to analyze genome-wide patterns of genetic variation in human populations. Since traditionally such studies surveyed only a small fraction of the genome, interpretation of the results was limited. RESULTS: We report here the results of the first whole genome resequencing-based analysis identifying genes that likely modulate high altitude adaptation in native Ethiopians residing at 3,500 m above sea level on Bale Plateau or Chennek field in Ethiopia. Using cross-population tests of selection, we identify regions with a significant loss of diversity, indicative of a selective sweep. We focus on a 208 kbp gene-rich region on chromosome 19, which is significant in both of the Ethiopian subpopulations sampled. This region contains eight protein-coding genes and spans 135 SNPs. To elucidate its potential role in hypoxia tolerance, we experimentally tested whether individual genes from the region affect hypoxia tolerance in Drosophila. Three genes significantly impact survival rates in low oxygen: cic, an ortholog of human CIC, Hsl, an ortholog of human LIPE, and Paf-AHalpha, an ortholog of human PAFAH1B3. CONCLUSIONS: Our study reveals evolutionarily conserved genes that modulate hypoxia tolerance. In addition, we show that many of our results would likely be unattainable using data from exome sequencing or microarray studies. This highlights the importance of whole genome sequencing for investigating adaptation by natural selection.
Title: Hormone-sensitive lipase deficiency in humans Zechner R, Langin D Ref: Cell Metab, 20:199, 2014 : PubMed
The breakdown of cellular fat stores fuels energy production and multiple anabolic processes. Albert et al. (2014) demonstrate that the lack of hormone-sensitive lipase, a member of the enzyme trio that catabolizes fat, has pronounced effects on lipid metabolism, glucose homeostasis, and cell signaling in humans.
