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

Pseudoacromegaly-A challenging entity in the endocrine clinic: A systematic review

OBJECTIVE

Pseudoacromegaly encompasses conditions with features of acromegaly/gigantism, but no growth hormone (GH) or insulin-like growth factor-1 (IGF-1) excess. We aimed to review published pseudoacromegaly cases evaluated due to clinical suspicion of acromegaly.

DESIGN/PATIENTS

PubMed/Medline search was conducted to identify reported pseudoacromegaly cases, which were systematically reviewed to ensure they met eligibility criteria: (1) presentation suggestive of acromegaly; (2) acromegaly excluded based on normal GH, IGF-1 and/or GH suppression on oral glucose tolerance test (OGTT-GH); (3) diagnosis of the pseudoacromegaly condition was established. Data were retrieved from each case and analysed collectively.

RESULTS

Of 76 cases, 47 were males, mean ages at presentation and at first acromegaloid symptoms were 28 ± 16 and 17 ± 10 years, respectively. Most common conditions were pachydermoperiostosis (47%) and insulin-mediated pseudoacromegaly (IMP) (24%). Acromegaloid facies (75%) and acral enlargement (80%) were the most common features. Measurement of random GH was reported in 65%, IGF-1 in 79%, OGTT-GH in 51%. GH excess was more frequently excluded based on two tests (53%). Magnetic resonance imaging (MRI) was performed in 30 patients, with pituitary adenoma or hyperplasia being reported in eight and three patients, respectively. Investigations differed between cases managed by endocrine and non-endocrine specialists, the former requesting more often IGF-1, OGTT-GH and pituitary MRI.

CONCLUSIONS

Pseudoacromegaly is a challenging entity that may be encountered by endocrinologists. Pachydermoperiostosis and IMP are the conditions most often mimicking acromegaly. Adequate assessment of GH/IGF-1 is crucial to exclude acromegaly, which may be better performed by endocrinologists. Pituitary incidentalomas are common and require careful judgement to prevent unnecessary pituitary surgery.

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.

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.

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.

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

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.

How to diagnose a lipodystrophy syndrome

The spectrum of adipose tissue diseases ranges from obesity to lipodystrophy, and is accompanied by insulin resistance syndrome, which promotes the occurrence of type 2 diabetes, dyslipidemia and cardiovascular complications. Lipodystrophy refers to a group of rare diseases characterized by the generalized or partial absence of adipose tissue, and occurs with or without hypertrophy of adipose tissue in other sites. They are classified as being familial or acquired, and generalized or partial. The genetically determined partial forms usually occur as Dunnigan syndrome, which is a type of laminopathy that can also manifest as muscle, cardiac, neuropathic or progeroid involvement. Gene mutations encoding for PPAR-gamma, Akt2, CIDEC, perilipin and the ZMPSTE 24 enzyme are much more rare. The genetically determined generalized forms are also very rare and are linked to mutations of seipin AGPAT2, FBN1, which is accompanied by Marfan syndrome, or of BANF1, which is characterized by a progeroid syndrome without insulin resistance and with early bone complications. Glycosylation disorders are sometimes involved. Some genetically determined forms have recently been found to be due to autoinflammatory syndromes linked to a proteasome anomaly (PSMB8). They result in a lipodystrophy syndrome that occurs secondarily with fever, dermatosis and panniculitis. Then there are forms that are considered to be acquired. They may be iatrogenic (protease inhibitors in HIV patients, glucocorticosteroids, insulin, graft-versus-host disease, etc.), related to an immune system disease (sequelae of dermatopolymyositis, autoimmune polyendocrine syndromes, particularly associated with type 1 diabetes, Barraquer-Simons and Lawrence syndromes), which are promoted by anomalies of the complement system. Finally, lipomatosis is currently classified as a painful form (adiposis dolorosa or Dercum's disease) or benign symmetric multiple form, also known as Launois-Bensaude syndrome or Madelung's disease, which are sometimes related to mitochondrial DNA mutations, but are usually promoted by alcohol. In addition to the medical management of metabolic syndrome and the sometimes surgical treatment of lipodystrophy, recombinant leptin provides hope for genetically determined lipodystrophy syndromes, whereas modifications in antiretroviral treatment and tesamorelin, a GHRH analog, is effective in the metabolic syndrome of HIV patients. Other therapeutic options will undoubtedly be developed, dependent on pathophysiological advances, which today tend to classify genetically determined lipodystrophy as being related to laminopathy or to lipid droplet disorders.