Atypical generalized lipoatrophy and severe insulin resistance due to a heterozygous LMNA p.T10I mutation

Lipoatrofia generalizada atípica e resistência insulínica grave devido à mutação p.T10I em heterozigose no gene LMNA

CLINICAL CASE REPORT

Atypical generalized lipoatrophy and severe insulin resistance due to a heterozygous LMNA p.T10I mutation

Lipoatrofia generalizada atípica e resistência insulínica grave devido à mutação p.T10I em heterozigose no gene LMNA

Patricia B. Mory; Felipe Crispim; Teresa Kasamatsu; Monica A. L. Gabbay; Sergio A. Dib; Regina S. Moisés

Disciplina de Endocrinologia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brasil

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ABSTRACT

Lipodystrophies are a group of heterogeneous disorders characterized by the loss of adipose tissue and metabolic complications. The main familial forms of lipodystrophy are Congenital Generalized Lipodystrophy and Familial Partial Lipodystrophy (FPLD). FPLD may result from mutations in the LMNA gene. Besides FPLD, mutations in LMNA have been shown to be responsible for other inherited diseases called laminopathies. Here we describe the case of a 15-year-old girl who was referred to our service due to diabetes mellitus and severe hypertriglyceridemia. Physical examination revealed generalized loss of subcutaneous fat, confirmed by DEXA (total body fat 8.6%). As the patient presented with pubertal-onset of generalized lipodystrophy and insulin resistance, molecular analysis of the LMNA gene was performed. We identified a heterozygous substitution in exon 1 (c.29C>T) predicting a p.T10I mutation. In summary, we describe an atypical phenotype of lipodistrophy associated with a de novo appearance of the p.T10I mutation in LMNA gene.

Keywords: Lamin A/C; Lipodystrophy; Insulin resistance; LMNA gene

RESUMO

As lipodistrofias são um grupo heterogêneo de doenças caracterizadas por perda de tecido adiposo e complicações metabólicas. As formas hereditárias mais importantes de lipodistrofias são: lipodistrofia congênita generalizada e lipodistrofia parcial familiar (LDPF). LDPF resulta de mutações no gene LMNA que codificam as lâminas tipo A. Além da LDPF, mutações no gene LMNA são responsáveis por outras doenças hereditárias, denominadas laminopatias. Descrevemos o caso de uma paciente de 15 anos de idade encaminhada por diabetes melito e hipertrigliceridemia grave. Ao exame físico, apresentava perda generalizada de gordura subcutânea que foi confirmada por DEXA (gordura corporal total 8,6%). Como a paciente apresentava perda de gordura de início na puberdade e resistência insulínica, foi realizada análise molecular do gene LMNA. Identificamos uma substituição em heterozigose no éxon 1 (c.29C>T), resultando na mutação p.T10I. Em sumário, um caso de fenótipo atípico de lipodistrofia generalizada devido à mutação de novo p.T10I no gene LMNA é descrito.

Descritores: Lâminas A/C; Lipodistrofia; Resistência insulínica; Gene LMNA

Lipodystrophies are a group of clinically heterogeneous disorders characterized by the loss of adipose tissue. Metabolic complications such as insulin resistance, impaired glucose tolerance, dyslipidemia and hepatic steatosis are generally present in affected patients and their severity is determined by the extent of fat loss (1,2). Lipodystrophies are classified according to their origin as familial (or genetic) and acquired types; and according to their clinical pattern of fat loss as generalized or partial.

The main familial forms of lipodystrophy are Congenital Generalized Lipodystrophy (CGL) or Berardinelli-Seip Syndrome (OMIM 269700) and Familial Partial Lipodystrophy (FPLD), Dunnigan variety (OMIM 51660). CGL is a rare autosomal recessive disorder characterized by a nearly complete absence of adipose tissue since birth or early infancy. Familial Partial Lipodystrophy, Dunnigan variety is an autosomal dominant disease characterized by gradual loss of adipose tissue from the extremities and trunk starting at the puberty, and subsequent fat accumulation on the face and neck. Two distinct genes were found to be responsible for the majority of CGL cases: the gene encoding the enzyme 1-acyl-glycerol phosphate acyltransferase 2 (AGPAT2) and the BSCL2 gene which encodes a protein called seipin of unknown function (3,4). FPDL may result from heterozygous mutations in the LMNA gene (5,6). This gene is located on chromosome 1q 21-22 and contains 12 exons. LMNA gene, through alternative splice, encodes lamin A and lamin C (7). Lamins are structural components of nuclear lamina and belong to the intermediate filament family of proteins. Besides FPLD, mutations in LMNA have been shown to be responsible for other inherited diseases such as Emery-Dreifuss muscular dystrophy type 2, dilated cardiomyopathy and conduction system disease, Hutchinson-Gilford Progeria Syndrome, Charcot-Marie-Tooth disorder and others (8-11). The term laminopathies is used to collectively call these diseases. Furthermore, LMNA mutations were found in atypical progeroid syndromes and in a pubertal-onset generalized lipodystrophy (12-14).

Here, we report the case of a patient with generalized lipodystrophy harboring the heterozygous p.T10I mutation in LMNA gene.

SUBJECTS AND METHODS

We studied a 15-year old girl who was referred to our hospital due to diabetes mellitus and hypertriglyceridemia. The patient and her parents were informed about the aims of the study and gave their written consent.

Molecular analysis of LMNA gene

DNA was extracted from peripheral blood leukocytes using a commercial kit (Puregene DNA Isolation Kit, Gentra System, Minneapolis, MN, USA). Exons 1-12 and the intron-exon boundaries of LMNA gene were amplified by PCR. The PCR products were directly sequenced with the use of Big Dye Terminator Cycle Sequencing Reaction Kit version 3.1 and analyzed on an ABI Prism 3100 Genetic Analyzer (Applied Biosystems, CA, USA).

Analysis of total and segmental body fat

Dual-energy-x-ray absorptiometry (DEXA) was used to evaluate whole-body and regional fat with the Hologic QDR-4500A equipment.

Biochemical measurements

Plasma glucose was determined by the glucose-oxidase method. Cholesterol contents of lipoproteins fractions and triglycerides were measured enzymatically. Plasma adiponectin concentrations were measured by radioimmunoassay (Linco Research, St Charles, MI, USA).

RESULTS

Case Report

In 2001, a 15-year-old girl was referred to our hospital due to diabetes mellitus and hypertriglyceridemia. Both conditions were diagnosed at age of 14 yr during investigation for delayed puberty. She was using NPH Insulin 14U/day, Metformin 1 g/day and Bezafibrate 400 mg/day. Physical examination revealed generalized loss of subcutaneous fat, including palmar aspects of hand and plantar aspects of feet. Prominent superficial veins and xantomas were seen on limbs (Figure 1). The patient referred that her subcutaneous fat gradually disappeared from the age of 11. Acanthosis nigricans was present on axilla and neck. Her weight was 33.9 kg, height 1.51 m and BMI 15 kg/m². Blood pressure was 150x100 mmHg. She had pubic hair at Tanner stage 4, however no breast development (Tanner stage 1). The liver was palpable at 6 cm below the right costal margin and spleen at 1 cm below the left costal margin. She presented thinning of scalp hair and sparse grey hair; no other progeroid characteristics were noted.

Laboratory measurements showed fasting plasma glucose of 143 mg/dl, HbA1C of 6.5%, triglycerides of 877 mg/dL, total cholesterol of 170 mg/dL, HDL-cholesterol of 20 mg/dL. Liver function tests showed alanine aminotransferase of 42 U/L (normal <31 U/L), aspartate aminotransferase of 36 U/L (normal <32 U/L), alkaline phosphatase of 562 U/L (normal <460 U/L) and γ glutamyltranspeptidase of 56 U/L (normal <32 U/L). Plasma adiponectin concentration of 0.6 ng/mL (reference range: 5-30 ng/mL). Blood electrolytes, renal function and thyroid hormone level were normal.

Abdominal ultrasonography showed hepatosplenomegaly and liver steatosis. Doppler echocardiography showed small atrial septum defect, ostium secundum type (4 mm), without any other abnormality. Dual energy x-ray absorptiometry was performed to evaluate whole-body and regional fat. The percentage of total body fat was 8.6%, corresponding to 2,924 g (reference range: 30.3 %± 1.5), legs 6.3% (reference range: 33.1%±1.5), arms 8.5% (reference range: 30.2%±1.8), trunk 7.8% (reference range: 29.0%±1.6). Therefore, a generalized loss of body fat was present. The reference values were reported by Mazess and cols. (15).

During the follow-up period a worsening on her metabolic state was observed coincident with a decrease in body fat (percentage of total body fat in 2004: 4.0%).The most recent evaluation showed an HbA1C of 13.5% despite high doses of insulin (1200 U/day) and triglycerides of 9,838 mg/dL despite the use of statin, fibrate and nicotinic acid.

Molecular analysis of LMNA gene

As the patient presented with pubertal-onset of generalized lipodystrophy and insulin resistance, molecular analysis of the LMNA gene was performed. We identified a heterozygous substitution in exon 1 (c.29C> T) predicting the substitution of threonine, a polar hydrophilic amino acid, to isoleucine, a non polar hydrophobic amino acid, at codon 10 (p.T10I mutation) in the N-terminal domain of the protein (Figure 2). The amino acid threonine at this position in LMNA gene is highly conserved across different species (Table 1), suggesting an important role in protein function. We did not observe this mutation in both of her parents, indicating that it is a de novo mutation.

DISCUSSION

Here we report the case of a patient with pubertal-onset generalized lipoatrophy, severe insulin resistance and hepatic steatosis harboring the p.T10I mutation in LMNA gene. The switch from polar hydrophilic threonine to non polar hydrophobic isoleucine in the lamin A/C N-terminal head may have functional consequences. Accordingly, Csoka et al showed in cultured fibroblasts that the p.T10I mutation causes severe consequences for nuclear morphology such as lobulations of the nuclear membrane, and some of these lobulations contained no chromatin, indicating that the lamina had detached from the chromatin (14).

Laminopathies are characterized by a complex genotype/phenotype relationship and LMNA mutations and redistribution of adipose tissue are more frequently observed in Familial Partial Lipodystrophy (Dunnigan variety) (6,16,17). Also, lipodystrophy and metabolic complications associated with insulin resistance have been reported in Mandibuloacral Dysplasia (18), and some affected patients were found to carry homozygous missense mutations in LMNA gene (19-21). The clinical phenotype of the patient reported herewith does not resemble any of these two conditions.

Recently, Caux et al described a male patient harboring the heterozygous R133L LMNA mutation that has some features similar to those found in our patient: pubertal-onset generalized lipodystrophy, insulin-resistant diabetes, hypertriglyceridemia and liver steatosis (13). However, hypertrophic cardiomyopathy and dissemined leucomelanodermic papules also described by Caux et al were not observed in our patient.

The p.T10I mutation was previously described by Csoka et al in a patient who was originally diagnosed with atypical progeria, but was later reclassified as Seip Syndrome based on generalized lipoatrophy, hyperglycemia and hypertriglyceridemia (14). However, no further information is provided such as the age of onset of these abnormalities, making difficult the comparison with this patient. Metabolic alterations such as insulin resistance, hypertriglyceridemia and liver steatosis are characteristics of lipodystrophies. Recent studies describe new phenotypes of metabolic laminopathies, even in the absence of obvious clinical lipoatrophy (22) or associated with premature ageing process (14).

Mutations associated with FPLD are frequently clustered in the LMNA region encoding the carboxi-terminal domain (2). The present observation illustrates a generalized lipoatrophy with a very severe insulin resistance due to a mutation in LMNA region encoding the N-terminal head. Previous reports of generalized lipoatrophy as a manifestation of laminopathy were also associated with mutations which affect the amino-terminal head domain or the α-helical rod domain of the protein (13,14,23). These observations pointed out that the heterogeneity of lipodystrophies as a manifestation of laminopathy.

In summary, here we describe an atypical phenotype of lipodystrophy associated with a de novo appearance of the p.T10I mutation in LMNA gene. The identification of mutation in this gene implies in a careful clinical and laboratory evaluation and follow-up of the affected patient. Also, family members should be screened for an early detection and adequate treatment.

Acknowledgment: This work was supported by a grant from Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp). No potencial conflict of interest relevant to this article was reported.

Received in 25/8/2008

Accepted in 17/10/2008

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Publication Dates

• Publication in this collection
  16 Jan 2009
• Date of issue
  Nov 2008

History

• Accepted
  17 Oct 2008
• Received
  25 Aug 2008