Lipodystrophy, Familial Partial, Type 2

A number sign (#) is used with this entry because familial partial lipodystrophy type 2 (FPLD2) is caused by heterozygous mutation in the gene encoding lamin A/C (LMNA; 150330) on chromosome 1q21.

Description

Familial partial lipodystrophy is a metabolic disorder characterized by abnormal subcutaneous adipose tissue distribution beginning in late childhood or early adult life. Affected individuals gradually lose fat from the upper and lower extremities and the gluteal and truncal regions, resulting in a muscular appearance with prominent superficial veins. In some patients, adipose tissue accumulates on the face and neck, causing a double chin, fat neck, or cushingoid appearance. Metabolic abnormalities include insulin-resistant diabetes mellitus with acanthosis nigricans and hypertriglyceridemia; hirsutism and menstrual abnormalities occur infrequently. Familial partial lipodystrophy may also be referred to as lipoatrophic diabetes mellitus, but the essential feature is loss of subcutaneous fat (review by Garg, 2004).

The disorder may be misdiagnosed as Cushing disease (see 219080) (Kobberling and Dunnigan, 1986; Garg, 2004).

Genetic Heterogeneity of Familial Partial Lipodystrophy

Familial partial lipodystrophy is a clinically and genetically heterogeneous disorder. Types 1 and 2 were originally described as clinical subtypes: type 1 (FPLD1; 608600), characterized by loss of subcutaneous fat confined to the limbs (Kobberling et al., 1975), and FPLD2, characterized by loss of subcutaneous fat from the limbs and trunk (Dunnigan et al., 1974; Kobberling and Dunnigan, 1986). No genetic basis for FPLD1 has yet been delineated. FPLD3 (604367) is caused by mutation in the PPARG gene (601487) on chromosome 3p25; FPLD4 (613877) is caused by mutation in the PLIN1 gene (170290) on chromosome 15q26; FPLD5 (615238) is caused by mutation in the CIDEC gene (612120) on chromosome 3p25; FPLD6 (615980) is caused by mutation in the LIPE gene (151750) on chromosome 19q13; and FPLD7 (606721) is caused by mutation in the CAV1 gene (601047) on chromosome 7q31.

Clinical Features

Dunnigan et al. (1974) described an autosomal dominant disorder in 2 families from the same region of northern Scotland. Features were symmetric lipoatrophy of the trunk and limbs with rounded, full face, tuberoeruptive xanthomata, acanthosis nigricans, and insulin-resistant hyperinsulinism. In 1 family, 6 females, 3 of whom were personally examined by the authors, were affected in 4 generations. In the other family, which was probably related to the first, 6 females in 3 generations were affected. This syndrome is distinct from congenital generalized lipodystrophy (see 608594), from progressive partial lipodystrophy (see 613779), which is a sporadic disorder associated with decreased levels of complement component C3, and from the acquired generalized lipodystrophy described by Lawrence (1946).

Greene et al. (1970) and Ozer et al. (1973) described a condition of fat accumulation around the neck, shoulders, upper back, and genitalia associated with lean muscular limbs, phlebectasia, insulin resistance, hyperglycemia, and type IV hyperlipoproteinemia. Affected members in the family of Greene et al. (1970) also had hyperuricemia. Successive generations were affected, but only females appeared to have the full-blown disorder.

Davidson and Young (1975) reported a family with familial partial lipodystrophy characterized by absence of subcutaneous fat from the limbs and lower trunk with sparing of the face and upper trunk. Although lipodystrophy was not seen in males, 5 males were diabetic. The authors suggested X-linked dominant inheritance of the disorder. See also the pedigree analysis of Wettke-Schafer and Kantner (1983), who discussed the possibility of X-linked dominant inheritance with lethality in hemizygous males.

Burn and Baraitser (1986) reported a family in which 5 members, including 1 male, were affected with familial partial lipodystrophy in an autosomal dominant pattern of inheritance. Clinical features included lipoatrophy of the limbs and trunk, with sparing of the face and neck. Affected members had muscular definition with variable muscular hypertrophy and prominent peripheral veins. Acanthosis nigricans and xanthomata were present. Laboratory studies showed hyperinsulinemia, hyperlipidemia, and insulin resistance.

Reardon et al. (1990) described partial lipodystrophy in a 2-year-old boy. There was complete absence of fat on the body and limbs, but the face and feet were spared and the hands were puffy. Classification of the case was considered difficult, but the distribution of loss of subcutaneous fat corresponded to that of FPLD type 2 (Dunnigan type) described in adults.

To investigate whether there is a unique pattern of fat distribution in men and women with FPLD, Garg et al. (1999) performed whole-body magnetic resonance imaging (MRI) in 1 male and 3 female patients from 2 pedigrees. MRI studies confirmed the clinical findings of near-total absence of subcutaneous fat from all extremities. Reduction in subcutaneous adipose tissue from the truncal area was more prominent anteriorly than posteriorly. Increased fat stores were observed in the neck and face. The authors concluded that FPLD results in a characteristic absence of subcutaneous fat from the extremities, with preservation of intermuscular fat stores.

The clinical features in families studied by Jackson et al. (1998) included a dramatic absence of adipose tissue in the limbs and trunk, more evident in females than in males, with fat retained on the face, in the retroorbital space, and at periserous sites. Jackson et al. (1998) noted that a syndrome with similar metabolic abnormalities, including insulin resistance, hyperinsulinemia, and dyslipidemia, has been referred to as 'metabolic syndrome X' (Reaven, 1988); see 605552.

Garg (2000) compared the anthropometric variables and prevalence of diabetes mellitus, dyslipidemia, hypertension, and atherosclerotic vascular disease among 17 postpubertal males and 22 females with FPLD from 8 pedigrees. All individuals completed a questionnaire, and fasting blood was analyzed for glucose, insulin, and lipoprotein concentrations. Both affected men and women had similar patterns of fat loss. Compared with the affected men, women had a higher prevalence of diabetes (18% and 50%, respectively; P = 0.05) and atherosclerotic vascular disease (12% and 45%, respectively; P = 0.04), and had higher serum triglycerides (median values, 2.27 and 4.25 mmol/L, respectively; P = 0.02) and lower HDL cholesterol concentrations (age-adjusted means, 0.94 and 0.70 mmol/L, respectively; P = 0.04). The prevalence of both hypertension and fasting serum insulin concentrations were similar. Garg (2000) concluded that females with FPLD are more severely affected with metabolic complications of insulin resistance than are males.

The common insulin resistance syndrome of obesity, dyslipidemia, hyperglycemia, and hypertension has a well-recognized association with atherosclerosis. Hegele (2001) studied the prevalence of coronary artery disease in a group of individuals with Dunnigan-type familial partial lipodystrophy, all of whom had mutations in the LMNA gene. All individuals had insulin resistance, with significantly more type II diabetes mellitus, hypertension, and dyslipidemia than in normal family control subjects. Eight of 23 individuals (35%) had identifiable endpoints of coronary artery disease (angina pectoris, myocardial infarction, or coronary artery bypass surgery); 1 of these individuals had also developed occlusive peripheral vascular disease. Only 1 control individual had coronary artery disease. Hegele (2001) concluded that Dunnigan-type familial partial lipodystrophy represents a single-gene model for the more common insulin resistance syndrome.

Caux et al. (2003) reported a 27-year-old man with generalized lipodystrophy, hepatic steatosis, insulin-resistant diabetes, hypertrophic cardiomyopathy, and leukomelanodermic papules. He had been diagnosed with hepatic steatosis at the age of 21 years, hypertriglyceridemia at 22 years, and diabetes at 25 years. The patient's appearance included square jaw, thin lips, high forehead, marked thinning of the eyebrows, pectus excavatum, and narrow shoulders. Generalized atrophy of subcutaneous fat resulted in sunken cheeks and muscular pseudohypertrophy of the 4 limbs. Multiple whitish papules on pigmented skin were present on the neck, trunk, and upper limbs and to a lesser extent on the lower limbs. The patient mentioned that his subcutaneous body fat progressively disappeared from the age of 14 years, after the onset of puberty. The development of the skin lesions occurred simultaneously. No acanthosis nigricans was present. Gray hair had been present since the age of 17 years. Muscular strength was normal, and no neurologic defects were detected. Cardiac involvement included concentric hypertrophy of the left ventricle without cavity dilatation, associated with thickened and regurgitant valves, aortic fibrotic nodules, and calcification of the posterior annulus. Doppler echocardiographic findings were similar to those described in aged patients. Abdominal MRI revealed an absence of body fat at both the subcutaneous and visceral levels. Osteopoikilosis, acroosteolysis, hypoplastic clavicles, wide sutures, and mandibular hypoplasia, previously described in mandibuloacral dysplasia (MAD; 248370), were not identified by bone x-rays. Typical symptoms of Werner syndrome (277700), such as cataracts, short stature, and skeletal anomalies, were absent. Family members were unaffected, and no consanguinity was reported. Genetic analysis identified a heterozygous mutation in the LMNA gene (R133L; 150330.0027). Vigouroux et al. (2003) emphasized that a striking feature in the patient reported by Caux et al. (2003) was muscular hypertrophy of the limbs, which contrasts with the muscular atrophy usually present in Werner syndrome. Muscular hypertrophy, along with insulin-resistant diabetes and hypertriglyceridemia, is more often associated with LMNA-linked Dunnigan lipodystrophy. Fibroblasts from this patient showed nuclear abnormalities identical to those described in Dunnigan lipodystrophy (Vigouroux et al., 2001).

Spuler et al. (2007) reported 13 FPLD2 patients with neuromuscular involvement. Twelve had muscle hypertrophy, 9 had severe myalgias, and 8 had multiple nerve entrapment syndromes. Skeletal muscle biopsies showed marked hypertrophy of type 1 and type 2 muscle fibers and nonspecific myopathic changes. Sural nerve biopsies showed numerous paranodal myelin swellings, or tomacula. Skeletal muscle myostatin (MSTN; 601788) mRNA was decreased in patients compared to controls, but no MSTN gene mutations were detected. FPLD2 muscle specimens had a large number of SMAD (see, e.g., 601595) molecules adhered to the nuclear membrane and not found within the nucleus, compared to normal muscle or muscle from a patient with a non-FPLD LMNA disease. Spuler et al. (2007) concluded that neuromuscular features of FPLD2 may result from disrupted SMAD-MSTN signaling.

Vantyghem et al. (2008) compared the fertility and occurrence of obstetric complications of women with familial partial lipodystrophy due to LMNA mutations with those of unaffected relatives, women from the general population, and women with polycystic ovary syndrome (PCOS). Data were obtained from clinical follow-up of 7 families with patients exhibiting mutations in LMNA (14 affected among 48 women). The mean number of live children per woman was 1.7 in affected patients versus 2.8 in nonaffected relatives. Fifty-four percent of LMNA-mutated women exhibited a clinical phenotype of PCOS, 28% suffered from infertility, 50% experienced at least one miscarriage, 36% developed gestational diabetes, and 14% experienced eclampsia and fetal death. Vantyghem et al. (2008) concluded that in these LMNA-linked lipodystrophic patients, the prevalence of PCOS, infertility, and gestational diabetes was higher than in the general population. Moreover, the prevalence of gestational diabetes and miscarriages was higher in lipodystrophic LMNA-mutated women than previously reported in PCOS women with similar body mass index. Women with lipodystrophies due to LMNA mutations are at high risk of infertility, gestational diabetes, and obstetrical complications and require reinforced gynecologic and obstetric care.

Inheritance

Although X-linked dominant inheritance had been suggested, affected pedigrees reported by Robbins et al. (1982), Jackson et al. (1997), and Peters et al. (1998) showed clear autosomal dominant inheritance.

Mapping

In a genomewide scan using highly polymorphic short tandem repeats (STRs) in individuals from 5 well-characterized FPLD pedigrees, Peters et al. (1998) mapped the disease locus to 1q21-q22. The maximum 2-point lod score obtained with a highly polymorphic microsatellite at D1S2624 at theta (max) = 0.0 was 5.84. Multipoint linkage analysis yielded a peak lod score of 8.25 between D1S305 and D1S1600. There was no evidence for genetic heterogeneity in these pedigrees.

Anderson et al. (1999) performed linkage and haplotype analysis with highly polymorphic microsatellite markers on a large, multigenerational Caucasian kindred of German ancestry with the Dunnigan form of familial partial lipodystrophy. The family showed affected members through at least 4 generations. The results yielded a maximum 2-point lod score of 4.96 at theta = 0 for marker D1S2721 and a maximum multipoint lod score of 6.27 near the same marker. The results of the haplotype analysis supported the minimal candidate region reported by Peters et al. (1998).

Jackson et al. (1998) ascertained 2 multigenerational families, with a combined total of 18 individuals with partial lipodystrophy. A genomewide linkage search using microsatellite markers provided conclusive evidence of linkage to 1q21 (D1S498, maximum lod score = 6.89 at theta = 0.00), with no evidence of heterogeneity. Haplotype and multipoint analysis supported the location of the locus (which they symbolized PLD, for partial lipodystrophy) within a 21.2-cM chromosomal region flanked by markers D1S2881 and D1S484.

Molecular Genetics

In 5 Canadian FPLD families, Cao and Hegele (2000) identified heterozygosity for a mutation in the lamin A/C gene (R482Q; 150330.0010). There were no differences in age, gender, or body mass index in Q482/R482 heterozygotes compared with R482/R482 homozygotes (normals) from these families; however, there were significantly more Q482/R482 heterozygotes who had definite partial lipodystrophy and frank diabetes. Also compared with the normal homozygotes, heterozygotes had significantly higher serum insulin and C-peptide (see 176730) levels. The LMNA heterozygotes with diabetes were significantly older than heterozygotes without diabetes.

In 6 families and 3 isolated cases of partial lipodystrophy, Shackleton et al. (2000) found heterozygosity for an R482W missense mutation in the LMNA gene (150330.0011), in the same codon as the R482Q mutation found in Canadian families by Cao and Hegele (2000). Shackleton et al. (2000) identified a third mutation in that codon, R482L (150330.0012), in another family with partial lipodystrophy.

Speckman et al. (2000) analyzed the LMNA gene in 15 families with partial lipodystrophy and identified the R482Q mutation in 5, the R482W mutation in 7, and a G465D mutation (150330.0015) in 1.

Schmidt et al. (2001) identified a family with partial lipodystrophy carrying the R482W missense mutation in the LMNA gene. Clinically, the loss of subcutaneous fat and muscular hypertrophy, especially of the lower extremities, started as early as in childhood. Acanthosis and severe hypertriglyceridemia developed later in life, followed by diabetes. Characterization of the lipoprotein subfractions revealed that affected children present with hyperlipidemia. The presence and severity of hyperlipidemia seem to be influenced by age, apolipoprotein E genotype, and the coexistence of diabetes mellitus.

Lanktree et al. (2007) analyzed the LMNA gene in 3 unrelated patients with FPLD2 and identified heterozygosity for 3 different missense mutations, all affecting only the lamin A isoform and each changing a conserved residue. Two of the mutations, D230N (150330.0042) and R399C (150330.0043), were 5-prime to the nuclear localization signal, which is not typical of LMNA mutations in FPLD2.

Genotype/Phenotype Correlations

In a family with an atypical form of FPLD, Speckman et al. (2000) identified an R582H mutation (150330.0016) in the LMNA gene. In a follow-up of this same family, Garg et al. (2001) reported that 2 affected sisters showed less severe loss of subcutaneous fat from the trunk and extremities with some retention of fat in the gluteal region and medial parts of the proximal thighs compared to women with typical FPLD2. Neither of the sisters with atypical FPLD2 had acanthosis nigricans or hirsutism, and only 1 had diabetes mellitus, borderline hypertriglyceridemia, and irregular menstrual periods. The sisters also tended to have lower serum triglycerides and higher HDL cholesterol concentrations compared to those with typical FPLD2. Both types had similar excess of fat deposition in the neck, face, intraabdominal, and intermuscular regions. Noting that the R582H mutation interrupts only the lamin A protein, Garg et al. (2001) suggested that in typical FPLD2, interruption of both lamins A and C causes a more severe phenotype than that seen in atypical FPLD2, in which only lamin A is altered.

Pathogenesis

Araujo-Vilar et al. (2009) studied 7 patients from 1 kindred with FPLD2 caused by an R482W mutation in the LMNA gene (150330.0011). Two had type 2 diabetes mellitus. As a group, the patients with FPLD2 were found to have significantly higher insulin resistance compared to 10 controls. The expression of LMNA in abdominal and peripheral adipose tissues was similar in both groups. In patients with FPLD2, thigh adipose tissue, but not abdomen adipose tissue, showed significantly decreased expression of PPARG2 (601487), RB1 (614041), cyclin D3 (CCND3; 123834), and LPL (609708) (67%, 25%, 38%, and 66%, respectively) compared to controls. There was an accumulation of prelamin A in the nuclear envelope of peripheral adipose tissue of patients with FPLD2. Electron microscopic analysis of adipocytes of patients with FPLD2 showed defects in the peripheral heterochromatin and a nuclear fibrous dense lamina. Collectively, the findings indicated that transcriptional activity of several genes involved in adipogenesis is altered in affected tissues of patients with FPLD2.