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Risk Factors for Diabetes in Familial Partial Lipodystrophy, Dunnigan Variety

¹ Division of Nutrition and Metabolic Diseases, Center for Human Nutrition, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
² Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan
³ National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
⁴ Division of Human Genetics, Department of Genetics and Pediatrics, Washington University School of Medicine, St. Louis, Missouri

	ABSTRACT

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OBJECTIVES—Familial partial lipodystrophy, Dunnigan variety (FPLD), is an autosomal dominant disorder due to missense mutations in the lamin A/C (LMNA) gene encoding nuclear lamina proteins. It is characterized by loss of subcutaneous fat from the extremities and trunk and accumulation of fat in the head and neck region beginning at puberty. Patients with FPLD are predisposed to metabolic complications of insulin resistance such as diabetes. We sought to identify risk factors for diabetes in patients with FPLD.

RESEARCH DESIGN AND METHODS—A cross-sectional study comparing clinical, biochemical, and anthropometric variables and LMNA genotypes in FPLD patients with and without diabetes.

RESULTS—We studied 52 women and 24 men with FPLD from 18 different families. Twenty-eight women (54%) but only four men (17%) had diabetes (P < 0.001); therefore further comparisons were mostly limited to women. Compared with women without diabetes, those with diabetes had higher BMI (median values 23 vs. 24 kg/m², respectively; P = 0.03), increased chin skinfold thickness (10 vs. 20 mm; P = 0.001), lower rates of nulliparity (60% vs. 28%; P = 0.04), and higher levels of fasting serum triglycerides (2.4 vs. 3.5 mmol/l; P < 0.001) but similar serum leptin levels (3.4 vs. 3.6 ng/ml; P = 0.9). The prevalence of diabetes was not related to age, menopausal status, family history of type 2 diabetes in unaffected relatives, or LMNA genotype.

CONCLUSIONS—We conclude that increased adiposity as reflected by excess subcutaneous fat accumulation in the chin region and parity may predispose women with FPLD to develop diabetes.

Abbreviations: FPLD, familial partial lipodystrophy, Dunnigan variety

	INTRODUCTION

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Familial partial lipodystrophy, Dunnigan variety (FPLD) (Mendelian Inheritance in Man #151660), is a rare monogenic adipose tissue disorder with increased predisposition of affected subjects to insulin resistance and its metabolic complications, such as glucose intolerance, diabetes, dyslipidemia, and hepatic steatosis (1–4). Patients with FPLD develop gradual loss of subcutaneous fat from the extremities and trunk starting at puberty. Subsequently, some accumulate excess fat in the head, neck, and intra-abdominal regions (5). The disorder is inherited in an autosomal dominant fashion and recently has been shown to be due to missense mutations in the gene encoding lamins A and C (LMNA) on chromosome 1q21–22 (6–9). Lamins A and C belong to the intermediate filament family of proteins and are structural components of nuclear lamina. Previously, we have shown that compared with affected men, women with FPLD are particularly predisposed to develop diabetes (10). However, the risk factors that predispose patients with FPLD to develop diabetes remain unclear. For example, it is not clear whether a particular LMNA mutation, the degree of fat loss from the extremities and trunk, or the excess fat deposition predisposes patients to develop diabetes. In the present study, therefore, we sought to determine the risk factors for the development of diabetes in a cross-sectional comparison of a large number of well-characterized patients with FPLD with and without diabetes.

	RESEARCH DESIGN AND METHODS

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Subjects
All subjects gave written informed consent. Appropriate institutional review boards approved the protocol. Only adults (>18 years of age) were included in this analysis. FPLD was diagnosed on the basis of characteristic phenotype and the presence of missense mutations in the LMNA gene. All unaffected relatives were genotyped for the presence of the missense mutation identified in their family and had only wild-type alleles. We studied 24 men and 52 women with FPLD belonging to 18 different families. All families were of European origin, except family F2600, which was of Asian Indian origin. Most of these pedigrees have been previously reported (7,9,11,12). All the families were evaluated at the University of Texas Southwestern Medical Center at Dallas, except F1000 and F2500 families (24 subjects), who were evaluated at the National Institutes of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland. Nineteen of these subjects (six women and three men with diabetes and five women and five men without diabetes) visited the General Clinical Research Center of the University of Texas Southwestern Medical Center at Dallas for evaluation; information and blood samples on the other 33 patients were obtained by mail as described previously (10).

Questionnaire
All subjects reported demographic data, date of birth, height, and weight, as well as health history, particularly related to the presence or absence of diabetes, dyslipidemia, hypertension, acanthosis nigricans, parity, menopausal status, menstrual irregularity, hirsutism, and polycystic ovaries and use of medications. Diabetes was diagnosed on the basis of previous history, use of hypoglycemic medications, or if fasting serum glucose concentration exceeded 7.0 mmol/l. Hypertension was diagnosed on self-report or use of antihypertensive medications or if either systolic or diastolic blood pressure exceeded 140 or 90 mmHg, respectively.

Anthropometry
In the 19 subjects evaluated at Dallas, skinfold thickness was measured with a Lange caliper (Cambridge Scientific Industries, Cambridge, MD) at the chin and five truncal (chest, mid-axillary, abdomen, subscapular, and suprailiac) and six peripheral (biceps, triceps, forearm, hip, thigh, and calf) sites on the right side of the body. The mean of three repeat measurements at each site was calculated.

Biochemical studies
Blood was collected after a 12-h overnight fast for analysis of HbA_1c and for serum chemistry profile, lipoproteins, insulin, and leptin concentrations. Fasting serum samples were analyzed for cholesterol, triglycerides, and HDL cholesterol as described previously (10). Blood HbA_1c was measured using ion exchange high-performance liquid chromatography (Bio-Rad Laboratories, Hercules, CA). Serum insulin and leptin levels were determined by radioimmunoassay using commercial kits (Linco Research, St. Charles, MO).

Mutational analysis
Mutational analysis of LMNA was performed on all the patients by direct sequencing of the coding region and the splice-site junctions, as described previously (7).

Statistical analyses
Categorical data were compared by Fisher’s exact test. The biochemical parameters and anthropometric data were compared using Wilcoxon’s rank-sum test. Data are expressed as median (range), and P value <0.05 was considered statistically significant.

	RESULTS

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All patients, except one man, were previously diagnosed to have diabetes. Forty-three percent of them were treated with insulin, 23% with oral hypoglycemic agents, and 34% with nonpharmacological measures, including diet and physical activity. The prevalence of diabetes among women was approximately three times higher than in men with FPLD (56% vs. 17%, respectively; P < 0.001). Although comparative data on genotypes, clinical characteristics, and biochemical parameters in both men and women with and without diabetes are presented, main conclusions are limited to the data on women because of small sample size of men with diabetes. Median age of onset of diabetes was 30 years (range, 17–51 years) in women and 34 years (25–39 years) in men. Whereas the prevalence of hypertension was similar in women and men (42% vs. 26%; P = 0.3), more women reported taking lipid-lowering medications (92% vs. 55%; P = 0.001).

Comparison of women with and without diabetes revealed similar age and prevalences of type 2 diabetes in unaffected relatives, acanthosis nigricans, polycystic ovarian syndrome, and premenopausal status (Table 1). Versus women without diabetes, however, those with diabetes had significantly higher BMI (P = 0.03), increased use of lipid-lowering medications (P = 0.002), and lower rates of nulliparity (P = 0.04) (Table 1). The prevalence of hypertension tended to be slightly higher among women with diabetes, although it did not reach statistical significance (P = 0.08).

Skinfold measurements were available in six women with diabetes and five women without diabetes, and in three men with diabetes and six men without diabetes. Versus women without diabetes, those with diabetes had significantly increased skinfold thickness at the chin (10.4 mm [7.3–14.7 mm] vs. 20.3 mm [17–33 mm], respectively; P = 0.01) and at the biceps (4.5 mm [3–5.7 mm] vs. 6 mm [4–8 mm]; P = 0.03) (Fig. 1A). There were no significant differences in the skinfold thickness of the other peripheral and truncal sites between women with and without diabetes (Fig. 1A). In comparison with normal values (13), all women with FPLD had markedly reduced peripheral skinfold thickness at the triceps and thigh regions; however, truncal skinfolds at the chest, axillary, subscapular, abdominal and suprailiac regions ranged from <10th percentile to >90th percentile. No statistically significant differences were seen in the skinfold measurements between the FPLD men with and without diabetes (Fig. 1B). All men tended to have reduced peripheral skinfold thickness compared with normal values (14).

View larger version (28K): [in this window] [in a new window]   Figure 1— Skinfold thickness at various anatomic sites in women (A) and men (B) with FPLD. , patients with diabetes; •, patients without diabetes. The shaded bars represent the median and 10th and 90th percentile values of skinfold thickness for normal women aged 18–55 years in A (13) and for normal men aged 18 to 61 years in B (14). Women with diabetes had more fat accumulation at the chin and biceps than those without diabetes (P < 0.05).

	CONCLUSIONS

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Another predisposing factor for diabetes in women was parity, as less nulliparous women had diabetes. Kritz-Silverstein et al. (17) reported that parity was an independent risk factor for future development of type 2 diabetes, but other studies have found that the magnitude of this effect is reduced after adjusting for age, socioeconomic status, and BMI (18). Pregnancy is a well-known diabetogenic state and is a time of efficient fat storage. Because pregnant women with FPLD may not be able to accumulate fat in most of the subcutaneous regions, which are affected by lipodystrophy, they may accumulate excess fat in the face, neck, and intraabdominal region, predisposing them to diabetes.

Previous studies have identified dyslipidemia, particularly hypertriglyceridemia, as a predisposing risk factor for type 2 diabetes (19,20). Consistent with those studies, hypertriglyceridemia was also associated with predisposition to diabetes among women with FPLD. However, this association may be due to poor glycemic control in FPLD women with diabetes. Of note, a previous study reported higher serum triglyceride concentrations in FPLD patients with diabetes even when glycemic control was excellent (21). The onset of hypertriglyceridemia has reportedly antedated the onset of hyperglycemia in FPLD patients (21,22). Women with diabetes also had higher serum uric acid levels than those without diabetes. Interestingly, fasting serum insulin levels were not significantly different among FPLD women with and without diabetes. However, only nine women with diabetes had fasting serum insulin concentrations available because those on hypoglycemic therapy were excluded from this analysis.

Our anthropometric data, although limited, indicate that severity of lipodystrophy does not differ among FPLD women with and without diabetes, as most of the peripheral and truncal skinfold thicknesses were similarly reduced in the two groups. Serum leptin levels also were similarly reduced in the women with and without diabetes, compared with normal women matched for BMI (21). We have recently reported that serum adiponectin levels are reduced in FPLD subjects with diabetes versus those without diabetes (4.3 [1.9–12.7] vs. 7.6 [2.7–23.2] µg/ml, respectively; P < 0.05) (22). Reduced plasma adiponectin levels have been reported in other insulin-resistant states as well (23,24). These data suggest that FPLD patients with diabetes may be more insulin resistant than those without diabetes.

Another important aim of the study was to identify if any particular LMNA variant carried a high risk of diabetes among FPLD subjects. On the basis of study of a small pedigree, we have previously reported that R582H mutation may cause mild lipodystrophy as well as less severe metabolic complications, possibly because this particular mutation in exon 11 of LMNA affects transcription of lamin A only, whereas other previously reported mutations in FPLD patients in exon 1 and 8 affect transcription of both lamins A and C (11). However, our study did not have enough patients with some of the rare LMNA mutations to perform meaningful comparisons. When the two most prevalent mutations among FPLD subjects (R482Q and R482W) were compared, women carrying R482Q had somewhat higher prevalence of diabetes than those carrying R482W; however, this difference did not achieve statistical significance. Therefore, overall, prevalence of diabetes was not related to specific LMNA mutations. However, it is likely that insulin resistance in some of the FPLD patients may be due to modifier alleles of other genes implicated in causing insulin resistance.

Interestingly, some of the well-recognized risk factors for development of type 2 diabetes, such as, age, family history of type 2 diabetes, hypertension, and acanthosis nigricans (25,26), were not predictive of diabetes in women with FPLD. It is likely that the LMNA mutation may impart such a high risk of developing diabetes that it overshadows potential influence of these established risk factors for type 2 diabetes. FPLD being a rare disease, we consider data on 76 individuals as a large collection of subjects. Nonetheless, compared with previous population-based studies in type 2 diabetes (26,27), the number of subjects in our study is certainly limited and thus, the study may have lacked power to identify some of these risk factors. The lack of power certainly affected comparison of FPLD men with and without diabetes, since only four men had diabetes. Our study did not assess dietary intake and physical activity, which may be important confounding variables. Further, our data were cross-sectional and thus confirmation of our findings will require prospective longitudinal studies.

We conclude that women with FPLD are more predisposed to diabetes than men. This tendency among women may be due to increased adiposity in regions not affected by lipodystrophy, as reflected by increased submental deposition of subcutaneous fat. Furthermore, parity may predispose women with FPLD to diabetes. Age, menopausal status, family history of type 2 diabetes, and LMNA variants do not predict predisposition to diabetes.

	Acknowledgments

 
The study was supported in part by the National Institute of Health Grants M01-RR00633 and R01-DK54387 and by the Southwestern Medical Foundation.

We are grateful to the patients and their families for participating in the studies; Angela Osborn for technical assistance and illustrations; Beverley Adams Huet for statistical analysis; Drs. David C. Robbins, Robert Kreisberg, Mark D. Shepherd, Andrea Dunaif, David Feinstein, Margo Denke, Irene Sills, Noralane M. Lindor, Tu T. Nguyen, Evelyn Cintron, and Stephen Aronoff for patient referral; and the staff at the General Clinical Research Center for patient care and support.

	Footnotes

 
Address correspondence and reprint requests to Abhimanyu Garg, Division of Nutrition and Metabolic Diseases, Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9052. E-mail: abhimanyu.garg{at}utsouthwestern.edu.

Received for publication 6 December 2002 and accepted in revised form 3 February 2003.

A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.

	References

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