Body Composition And Bone Mineral Differences According to Lamin A (LMNA) Genotype in Familial Partial Lipodystrophy Type 2

Abstract

Phenotypic heterogeneity is well known in Familial Partial Lipodystrophy Type 2 (FPLD2), a rare form of adipose tissue disorder caused by pathogenic mutations in LMNA gene. Animal studies from our group have identified an association between adipose tissue loss and an increase in bone mineral density (BMD) in a mouse model with adipose tissue specific knockout of LMNA gene. Aiming to translate this observation to patients with FPLD2, we analyzed body composition data obtained by dual X-ray absorptiometry from 61 patients diagnosed with FPLD2 and 61 individuals with no diagnosis of FPLD (nFPLD) matched for sex, age and body mass index. As expected, we observed lower total fat mass in FPLD2 patients compared to nFPLD (15.8±9.3 kg vs. 28.5±12.4 kg, p=0.001), as well as lower fat mass in regions of arms, legs and trunk. Interestingly, patients with FPLD2 showed lower bone mineral density (BMD) compared to nFPLD 1.0±0.2 g/cm3 vs 1.2±0.1 g/cm3, p=0.01) and lower t-score (0.2±1.8 vs.1.5±1.2). We then aimed to determine if the patients with FPLD2 displayed differences with respect to genotype. For these analyses, the FPLD2 group was divided according to the pathogenic variant; 42 with mutations on the hot spot codon of the LMNA gene (R482: 50.2 ± 164.8 years, 76% women) and 19 with non-hot spot codon mutations (nR482: 44.8 ± 12.8 years, 78% women). Patients in the R482 group were older when they were first diagnosed with lipodystrophy (39.6 ± 18.6 years vs. 36.5 ± 12.3 years, p=0.05). Also, nR482 group presented with more progeroid characteristics. Patients in n-R482 group also had lower weight compared to R482 and nFPLD groups (64.4±14.4 vs. 73.3±18.5 and 77.6±16.6 kg, p=0.01), as well as lower total fat mass (15.3±5.1 vs. 15.8±9.3 and 25.7±11.4 kg, p=0.01) and fat mass ratio (5.8±1.9 vs. 5.9±3.1 and 9.0±4.1, p= 0.01). Control group bone mass was significantly higher in arms, legs and trunk compared to the R482 and nR482 groups. Moreover, the R482 group had lower bone mass in the legs compared to nR482 (690.5±227.2 vs.703.5±95.3 g, p=0.01), while showing higher trunk bone mass (676.4±266.7 vs. 674.1±79.3, p=0.04), in addition to greater fat mass in the legs (3.3±1.6 vs. 2.6±0.7 kg, p=0.05) and trunk areas (10.3±6.1 vs. 10.0±4.2 kg, p=0.03). There were no differences in total bone mass, BMD, and t-scores, according to genotype. Our data showed more fat preservation in LMNA R482 than nR482, presumably leading to a later lipodystrophy diagnosis. Furthermore, bone mass in different regions may be affected by LMNA genotype; however, more studies are needed to define the bone phenotype and fracture risk in FPLD2 population fully.