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Identification and Characterisation of a Novel Pathogenic Mutation in the Human Lipodystrophy Gene AGPAT2 : C48R: A Novel Mutation in AGPAT2.

ABSTRACT: Loss-of-function mutations in AGPAT2, encoding 1-acylglycerol-3-phosphate-O-acyltransferase 2 (AGPAT2), produce congenital generalised lipodystrophy (CGL). We screened the AGPAT2 gene in two siblings who presented with pseudoacromegaly, diabetes and severe dyslipidaemia and identified a novel mutation in AGPAT2 causing a single amino acid substitution, p.Cys48Arg. We subsequently investigated the molecular pathogenic mechanism linking both this mutation and the previously reported p.Leu228Pro mutation to clinical disease. Wild-type and mutant AGPAT2 were expressed in control and AGPAT2-deficient preadipocyte cell lines. mRNA and protein expression was determined, and the ability of each AGPAT2 species to rescue adipocyte differentiation in AGPAT2-deficient cells was assessed. Protein levels of both p.Cys48Arg and p.Leu228Pro AGPAT2 were significantly reduced compared with that of wild-type AGPAT2 despite equivalent mRNA levels. Stable expression of wild-type AGPAT2 partially rescued adipogenesis in AGPAT2 deficient preadipocytes, whereas stable expression of p.Cys48Arg or p.Leu228Pro AGPAT2 did not. In conclusion, unusually severe dyslipidaemia and pseudoacromegaloid overgrowth in patients with diabetes should alert physicians to the possibility of lipodystrophy. Both the previously unreported pathogenic p.Cys48Arg mutation in AGPAT2, and the known p.Leu228Pro mutation result in decreased AGPAT2 protein expression in developing adipocytes. It is most likely that the CGL seen in homozygous carriers of these mutations is largely accounted for by loss of protein expression.

SUBMITTER: Ramanathan N

PROVIDER: S-EPMC3565662 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Identification and Characterisation of a Novel Pathogenic Mutation in the Human Lipodystrophy Gene AGPAT2 : C48R: A Novel Mutation in AGPAT2.

Ramanathan N N Ahmed M M Raffan E E Stewart C L CL O'Rahilly S S Semple R K RK Raef H H Rochford J J JJ

JIMD reports 20121021

Loss-of-function mutations in AGPAT2, encoding 1-acylglycerol-3-phosphate-O-acyltransferase 2 (AGPAT2), produce congenital generalised lipodystrophy (CGL). We screened the AGPAT2 gene in two siblings who presented with pseudoacromegaly, diabetes and severe dyslipidaemia and identified a novel mutation in AGPAT2 causing a single amino acid substitution, p.Cys48Arg. We subsequently investigated the molecular pathogenic mechanism linking both this mutation and the previously reported p.Leu228Pro mu ...[more]

PMID: 23430550

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Project description:Abstract Background: Congenital generalized lipodystrophy (CGL) is a rare inherited disease characterized by widespread loss of subcutaneous fat and severe metabolic abnormalities. Metreleptin, a synthetic analog of leptin, is a treatment modality that has been shown to decrease fasting triglycerides, fasting glucose, and HbA1c. Metformin use in infants has only been described in a few case reports of CGL and Donohue syndrome (insulin receptor mutation), and there is no established dosing for this age group. We report metreleptin, insulin, and metformin use in an infant with type 1 CGL who presented with marked hypertriglyceridemia, hypoleptinemia, hyperglycemia, and transaminitis. Clinical Case: A 2-month-old African American female born SGA at term presented to her primary care physician for a well child check where she was noted to have poor weight gain, hyperphagia, and abdominal distension. She was subsequently admitted for failure to thrive with weight z-score of -2.17 and length z-score of -0.15. Initial labs were notable for triglycerides of 5,167 mg/dL, HDL 10 mg/dL, blood glucose 324 mg/dL, ALT 212 units/L, AST 215 units/L, and bicarbonate of 17 mmol/L. A random insulin level was elevated at 257 mcIU/mL. Adiponectin was undetectable and leptin was low at 0.3 ng/mL. Hemoglobin A1c was in diabetes mellitus range at 8.9%. She was started on detemir 1.0 units/kg/day on day 1 (titrated to a maximum dose of 4.4 units/kg/day) and metformin 50 mg/kg/day on day 3 of hospitalization. By day 4, triglycerides decreased to 758 mg/dL, AST to 119 units/L and ALT to 124 units/L. Pre-prandial glucoses improved ranging from 113 to 138 mg/dL. As her insurance denied coverage for detemir, she was discharged home on glargine 0.7 units/kg/day and metformin suspension. One month later, she was started on subcutaneous metreleptin, and glargine was discontinued. At 5 months of age, she had triglycerides 229 mg/dl, normal liver enzymes, and normal blood glucoses while on 0.056 mg/kg/day of subcutaneous metreleptin and metformin. Medications were well tolerated without side effects. She had improved growth and met all developmental milestones. Genetic evaluation revealed that she was homozygous for a pathogenic variant, c.589-2A>G; p.Gln196fs*228 (rs116807569), in the AGPAT2 gene. Conclusion: Leptin is important in regulation of lipid and glucose metabolism, and patients with CGL are deficient due to lack of adipose tissue. Metabolic abnormalities, including stabilization of glucoses and improved hypertriglyceridemia, in our patient markedly improved with initiation of metreleptin, metformin, and insulin. We present successful dosing of these treatment modalities without adverse reactions in an infant with CGL.

Project description:BACKGROUND: Congenital generalized lipodystrophy (CGL) or Berardinelli-Seip congenital lipodystrophy (BSCL) is a rare genetic syndrome characterized by the absence of adipose tissue. As CGL is thought to be related to malfunctions in adipocyte development, genes involved in the mechanisms of adipocyte biology and maintenance or differentiation of adipocytes, especially transcription factors are candidates. Several genes (BSCL1-4) were found to be associated to the syndrome but not all CGL patients carry mutations in these genes. METHODS AND RESULTS: In a patient with CGL and insulin resistance we investigated the known candidate genes but the patient did not carry a relevant mutation. Analyses of the insulin activated signal transduction pathways in isolated fibroblasts of the patient revealed a postreceptor defect altering expression of the immediate early gene c-fos. Sequence analyses revealed a novel homozygous point mutation (c.-439, T?A) in the patients' c-fos promoter. The point mutation was located upstream of the well characterized promoter elements in a region with no homology to any known cis-elements. The identified mutation was not detected in a total of n=319 non lipodystrophic probands. In vitro analyses revealed that the mutation facilitates the formation of a novel and specific protein/DNA complex. Using mass spectrometry we identified the proteins of this novel complex. Cellular investigations demonstrate that the wild type c-fos promoter can reconstitute the signaling defect in the patient, excluding further upstream signaling alterations, and vice versa the investigations with the c-fos promoter containing the identified mutation generally reduce basal and inducible c-fos transcription activity. As a consequence of the identified point mutation gene expression including c-Fos targeted genes is significantly altered, shown exemplified in cells of the patient. CONCLUSION: The immediate-early gene c-fos is one essential transcription factor to initiate adipocyte differentiation. According to the role of c-fos in adipocyte differentiation our findings of a mutation that initiates a repression mechanism at c-fos promoter features the hypothesis that diminished c-fos expression might play a role in CGL by interfering with adipocyte development.

Dataset Information

Identification and Characterisation of a Novel Pathogenic Mutation in the Human Lipodystrophy Gene AGPAT2 : C48R: A Novel Mutation in AGPAT2.

Publications

Identification and Characterisation of a Novel Pathogenic Mutation in the Human Lipodystrophy Gene AGPAT2 : C48R: A Novel Mutation in AGPAT2.

Similar Datasets

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