Diagnóstico genético e caracterização genótipo/fenótipo de variantes do gene PPARG, precursor da lipodistrofia familiar parcial do tipo 3 em pacientes do nordeste brasileiro

Abstract

Lipodystrophy type 3 (FPLD3) has been described as molecularly associated with the PPARG gene, with predominantly missense variants on chromosome 3. The syndrome causes loss of adipose tissue in the upper and lower limbs, hips, and face. It is generally associated with metabolic disorders such as type 2 diabetes, insulin resistance, hypertriglyceridemia, and liver dysfunction. Therefore, the objective of this work was to molecularly diagnose and characterize the genotype/phenotype of patients with a clinical diagnosis of LPF3 recruited by the endocrinology clinic of the Hospital Universitário Onofre Lopes.To this end, a clinical evaluation was carried out, oral swabs and blood samples were collected. Biochemical analyses and dosages of the hormones adiponectin and leptin were performed using the ELISA technique to evaluate the metabolic disorders inherent to FPLD3. The nextgeneration sequencing (NGS) technique was chosen to diagnose the variants through a panel of genes related to lipodystrophies including LMNA and PPARG. To confirm the NGS data, amplification of genetic material was carried out by conventional PCR and Sanger sequencing using primers specifically designed for this work. The tools used for bioinformatic analysis of the variants were Poly-Phen2, TCoffee, and Mutation Taster. It was observed that the patients presented clinical characteristics compatible with the presence of lipodystrophy, such as loss of adipose tissue in the extremities, hypertriglyceridemia, and steatosis, in addition to a reduced adiponectin and leptin dosage within normal limits concerning the reference value for the index of corresponding body mass. Molecularly, new heterozygous variants located at positions c.533T>C promoting the replacement of the amino acid leucine by proline at 178 (p.Leu178Pro) and c.641C>T promoting the replacement of the amino acid proline by leucine at 214 were identified and confirmed in three patients. (p.Pro214Leu). The variants respectively affect the DBD domain of the protein, responsible for binding PPAR to the promoter region of target genes, and the Hinge region, involved in the interaction with coactivators and corepressors. Through bioinformatic analysis of each identified variant and its comparative alignment with the wild type, it was observed that the scores corroborated what was observed clinically, classifying the variants as harmful to their function. This was the first study to molecularly characterize patients with familial partial lipodystrophy type 3 with the c.533T>C and c.641C>T variants in the global literature.