OR2-002 – The risk of FMF in MEFV heterozygotes

International audienc

Loss of thymidine phosphorylase activity disrupts adipocyte differentiation and induces insulin-resistant lipoatrophic diabetes.

BACKGROUND: Thymidine phosphorylase (TP), encoded by the TYMP gene, is a cytosolic enzyme essential for the nucleotide salvage pathway. TP catalyzes the phosphorylation of the deoxyribonucleosides, thymidine and 2'-deoxyuridine, to thymine and uracil. Biallelic TYMP variants are responsible for Mitochondrial NeuroGastroIntestinal Encephalomyopathy (MNGIE), an autosomal recessive disorder characterized in most patients by gastrointestinal and neurological symptoms, ultimately leading to death. Studies on the impact of TYMP variants in cellular systems with relevance to the organs affected in MNGIE are still scarce and the role of TP in adipose tissue remains unexplored. METHODS: Deep phenotyping was performed in three patients from two families carrying homozygous TYMP variants and presenting with lipoatrophic diabetes. The impact of the loss of TP expression was evaluated using a CRISPR-Cas9-mediated TP knockout (KO) strategy in human adipose stem cells (ASC), which can be differentiated into adipocytes in vitro. Protein expression profiles and cellular characteristics were investigated in this KO model. RESULTS: All patients had TYMP loss-of-function variants and first presented with generalized loss of adipose tissue and insulin-resistant diabetes. CRISPR-Cas9-mediated TP KO in ASC abolished adipocyte differentiation and decreased insulin response, consistent with the patients' phenotype. This KO also induced major oxidative stress, altered mitochondrial functions, and promoted cellular senescence. This translational study identifies a new role of TP by demonstrating its key regulatory functions in adipose tissue. CONCLUSIONS: The implication of TP variants in atypical forms of monogenic diabetes shows that genetic diagnosis of lipodystrophic syndromes should include TYMP analysis. The fact that TP is crucial for adipocyte differentiation and function through the control of mitochondrial homeostasis highlights the importance of mitochondria in adipose tissue biology

The Contribution of SAA1 Polymorphisms to Familial Mediterranean Fever Susceptibility in the Japanese Population

Background/Aims: Familial Mediterranean Fever (FMF) has traditionally been considered to be an autosomal-recessive disease, however, it has been observed that substantial numbers of patients with FMF possess only 1 demonstrable MEFV mutation. The clinical profile of familial Mediterranean fever (FMF) may be influenced by MEFV allelic heterogeneity and other genetic and/or environmental factors. Methodology/Principal Findings: In view of the inflammatory nature of FMF, we investigated whether serum amyloid A (SAA) and interleukin-1 beta (IL-1β) gene polymorphisms may affect the susceptibility of Japanese patients with FMF. The genotypes of the -13C/T SNP in the 5′-flanking region of the SAA1 gene and the two SNPs within exon 3 of SAA1 (2995C/T and 3010C/T polymorphisms) were determined in 83 Japanese patients with FMF and 200 healthy controls. The same samples were genotyped for IL-1β-511 (C/T) and IL-1 receptor antagonist (IL-1Ra) variable number of tandem repeat (VNTR) polymorphisms. There were no significant differences between FMF patients and healthy subjects in the genotypic distribution of IL-1β -511 (C/T), IL-1Ra VNTR and SAA2 polymorphisms. The frequencies of SAA1.1 allele were significantly lower (21.7% versus 34.0%), and inversely the frequencies of SAA1.3 allele were higher (48.8% versus 37.5%) in FMF patients compared with healthy subjects. The frequency of -13T alleles, associated with the SAA1.3 allele in the Japanese population, was significantly higher (56.0% versus 41.0%, p = 0.001) in FMF patients compared with healthy subjects. Conclusions/Significance: Our data indicate that SAA1 gene polymorphisms, consisting of -13T/C SNP in the 5′-flanking region and SNPs within exon 3 (2995C/T and 3010C/T polymorphisms) of SAA1 gene, are associated with susceptibility to FMF in the Japanese population