A Novel PPARG R212W Variant Causes Familial Partial Lipodystrophy Type 3: Clinical Presentation and Functional Characterization.

Familial partial lipodystrophy type 3 (FPLD3) is a rare autosomal dominant disorder caused by mutations in peroxisome proliferator-activated receptor gamma(PPARG), which encodes the key adipogenic transcription factor peroxisome proliferator-activated receptor gamma(PPARγ). Clinical diagnosis is challenging due to phenotypic overlap with common metabolic syndromes. We identified a novel PPARG variant in a Chinese family and performed comprehensive functional characterization to elucidate its pathogenic mechanism. The proband, a 15-year-old boy presenting with atypical fat distribution, severe insulin resistance, hypertriglyceridemia, and pancreatitis, underwent clinical evaluation and whole-exome sequencing. The identified variant was confirmed by Sanger sequencing. Its functional impact was assessed through in silico modeling, luciferase reporter assays, protein stability analysis (cycloheximide chase), and evaluation of mitochondrial function (JC-1 staining) and adipocyte gene expression in cellular models. A heterozygous PPARG c.634C>T (p.Arg212Trp, R212W) variant was identified and segregated with the phenotype. Functional studies revealed that the R212W mutant exhibits a partial loss of transcriptional activity (~40% of wild-type) while retaining ligand sensitivity. Crucially, we demonstrated that the mutant protein has significantly reduced stability due to accelerated degradation. In adipocyte models, R212W expression led to impaired mitochondrial membrane potential, depleted cellular ATP levels, and downregulated expression of key metabolic genes (glucose transporter 4[GLUT4], adiponectin[ADIPOQ], fatty acid binding protein 4[FABP4], lipoprotein lipase[LPL], perilipin 1[PLIN1]). These functional deficits were partially rescued by treatment with the PPARγ agonist rosiglitazone. We report a novel pathogenic PPARG R212W variant associated with FPLD3. Our data extend beyond a simple loss-of-function model by establishing a multi-faceted pathogenic mechanism involving protein destabilization, mitochondrial dysfunction, and cellular bioenergetic failure. The partial rescue by rosiglitazone suggests a potential therapeutic avenue. This study underscores the importance of integrating clinical phenotyping with deep functional analysis to diagnose and understand rare monogenic lipodystrophies.