Since Berardinelli first described congenital generalized lipodystrophy in 1954 (1
), more than 100 patients have been reported. The major clinical characteristics of this rare syndrome include severe insulin resistance and lipodystrophy at birth or in early infancy (3
). The high prevalence of parental consanguinity in affected individuals has been well documented, suggesting autosomal recessive transmission. Garg et al.
) undertook a genome-wide scan in 17 well-characterized pedigrees of Turkish, Caucasian, African, Hispanic, and Chinese origins and identified a locus (BSCL1
) on chromosome 9q34 (near marker D9S1818) and also showed at least one other locus in CGL. Recently, they identified homozygous or compound heterozygous mutations in the AGPAT2
gene among CGL-affected individuals showing linkage to 9q34 (11
). Magre et al.
) studied 29 families and 17 additional patients from Turkey, Norway, Italy, United Kingdom, Brazil, France, Lebanon, Portugal, and India and identified a locus (BSCL2
) within the 2.5-Mb interval flanked by markers D11S4076 and D11S480 on chromosome 11q13 using a genome-wide analysis. Sequence analysis of genes located in the 11q13 interval disclosed mutations in a gene homologous to the murine guanine nucleotide-binding protein (G protein), γ3-subunit-linked gene (Gng3lg
) in all BSCL2
-linked families (10
Our studies in 33 subjects from 26 CGL families and one Brunzell syndrome family represents one of the largest studies of CGL reported to date. We found four mutations in AGPAT2 and five mutations in Gng3lg, which explained the CGL phenotype in all but four subjects. Three of the mutations we found in AGPAT2 are novel, two of which predict premature chain termination and a truncated protein: A712T (Lys215X) and 636C3A (Phe189X). summarizes all mutations in AGPAT2 (A) and Gng3lg (B) identified to date.
FIG. 4 Schematic of mutations in Gng3lg (A) and AGPAT2 (B). Rectangles represent exons and lines between rectangles represent introns (not drawn to scale). Mutations that are underlined and in bold are new mutations identified in this study, mutations that are (more ...)
Eighteen affected individuals from 15 Caucasian families (CGL-F1 through -F15; ) who lived in a geographically localized region of Serido county of Rio Grande do Norte State in northeastern Brazil harbored the same homozygous mutation in Gng3lg
(669insA). The same mutation was described previously by Magre et al.
) in a subject of Portuguese origin in South Africa. In this region of Brazil, the vast majority of Caucasians are known to have originated from Portugal, and thus it is likely that 669insA in Gng3lg
arose from a single founder of Portuguese origin. Indeed, affected individuals were found to be homozygous for the same flanking short tandem repeat markers within this region of chromosome 11q13 (data not shown). Although all 18 individuals homozygous for this mutation had several of the cardinal manifestations of congenital generalized lipodystrophy, including lipoatrophy (body mass index, mean ± sd
= 20.4 ± 3.5 kg/m2
), acromegaloid dysmorphy, and muscular hypertrophy, other features were present in some but not all of the subjects [i.e.
hypertriglyceridemia (89% of subjects), acanthosis nigricans (82% of subjects), hyperinsulinemia (75% of subjects), external genitalia enlargement (69% of subjects), umbilical hernia (60% of subjects), low plasma leptin concentration (59% of subjects), diabetes (56% of subjects; age at onset of diabetes, 2–16 yr), hepatomegaly (50% of subjects), mental retardation (29% of subjects), splenomegaly (12% of subjects), and hirsutism (10% of female subjects)]. Thus, despite harboring the same mutation, subjects had widely divergent clinical manifestations, suggesting modifying influences of other genes and/or environment.
A Brazilian female (CGL-F16) with CGL and severe insulin resistance (17
), unrelated to Brazilian families CGL-F1-F15, had a Gng3lg
mutation (645insAA). The same mutation was found in another Brazilian case by Magre et al.
). Subject CGL-F17 lived in Canada, was of Indian origin, and had 980delC, which was previously described in a CGL case from India (10
). The study subject CGL-F18 carried the diagnosis of acquired generalized lipodystrophy. This Lebanese subject had a 368delGTATC mutation in Gng3lg
previously described in subjects with lipodystrophy of Lebanese origin (10
). Thus, these findings are more likely to reflect a founder effect, although we cannot rule out the possibility of de novo
mutations in Gng3lg
We found three novel missense mutations in AGPAT2,
two in a Brazilian female (CGL-F20), who was found to be a compound heterozygote (IVS3-1G→C and C636A, Phe189X), and one in two affected female siblings from family CGL-F19 (A712T, Lys215X). Brazilian subject CGL-F21 was a female who had a 317–588del of AGPAT2
, which also is most likely to have arisen in Portugal because this same mutation was described in a subject from Portugal, and European settlers from this region of Brazil are known to have originated from Portugal (11
We did not find mutations in either Gng3lg
in four subjects. Affected members of family CGL-F23, in addition to lipodystrophy, had neurodegenerative disorder and congenital cataracts. The proband from consanguineous pedigree CGL-F24 also had idiopathic pulmonary fibrosis and premature puberty. An 18-ar-old white female (CGL-F25) with lipodystrophy, diabetes, multiple xanthomas, bilateral cataracts, hemorrhagic pancreatitis, and cardiomyopathy also did not have mutations in Gng3lg
. Van Maldergem et al.
) also identified three families from a total 44 families for which they did not find a mutation in either Gng3lg
. It is possible that these subjects may have mutations in regions of Gng3lg
not studied (i.e.
regulatory elements in flanking regions or introns) or may have mutations in yet-to-be identified genes that cause related lipodystrophic syndromes.
Reports of cases with generalized lipodystrophy indicate phenotypic variation. Subjects with Brunzell syndrome typically have congenital generalized lipodystrophy with cystic angiomatosis of the long bones (13
). It has been suggested that Brunzell syndrome might have the same genetic etiology as BSCL (http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=272500
). However, others have suggested that Brunzell syndrome could be a separate entity (20
). Two sisters (subjects B-F1-1 and B-F1-2) from an African-American pedigree had congenital generalized lipodystrophy, cystic angiomatosis of long bones, and primary amenorrhea, attributed to polycystic ovaries. The brother (subject B-F1-3), in whom systemic angiomatosis was not detected, and both affected sisters carried the same splice site mutation (IVS4–2A→G) in AGPAT2
, showing directly that Brunzell syndrome is a clinical and genetic variant of CGL. Van Maldergem et al.
) also recently reported a mutation in Gng3lg
in a subject with Brunzell syndrome.
Our studies of a relatively large number of CGL subjects with mutations in both AGPAT2
provided the opportunity to compare clinical characteristics of subjects with each genetic etiology. Although definitive conclusions cannot be made, it appears that the two genetic etiologies of CGL have very similar, albeit variable, clinical characteristics. One notable exception is that mental retardation appears to be associated with Gng3lg
mutations but not AGPAT2
mutations (). A similar observation was made by Van Maldergem et al.
), suggesting that Gng3lg
plays a role in brain development or function, although we cannot rule out the possibility that the mental retardation was due to consanguinity and homozygosity for one or more mutations at other loci.
In summary, these studies have led to several novel findings. First, in our relatively large sample set, mutations in AGPAT2 and Gng3lg were approximately equally prevalent in patients with CGL. Second, there do not appear to be any major distinguishing phenotypic characteristics between subjects with AGPAT2 or Gng3lg mutations, with the possible exception of mental retardation, which appears to be associated with Gng3lg mutations but not AGPAT2 mutations. Third, studies of 18 subjects from the same locale in Brazil with the same mutation in Gng3lg show that there is great phenotypic variability in clinical manifestations, suggesting modifying effects of other genes or environmental factors. Finally, we show that Brunzell syndrome may be caused by mutations in AGPAT2. Future functional studies of Gng3lg and AGFAT2 will undoubtedly unveil greater insights into the clinical spectrum of lipodystrophy disorders as well as adipose tissue biology.