Vitamin K deficiency contributes to pathological calcification which underlies the clinical picture of pseudoxanthoma elasticum (PXE), an inherited autosomal recessive disease. A substantial proportion of vitamin K, namely the K2 form (menaquinones), is produced by gut microbiota. In healthy volunteers fecal levels of the major menaquinone producers, Escherichia coli and Bacteroides species, are approximately 5 and 9 log10 CFU/g dry weight respectively. There is however a lack of data on gut microbiota in PXE patients. The objective of our project is to demonstrate a potential association between gut microbiota composition, plasma levels of various forms of vitamin K and severity of clinical manifestations in PXE patients.~This study will be performed as Research surrounding bio collection Clinical and biological exploration of PXE patients kept at the Center of Biological Resources of Angers University Hospital (bio collection n° DC 20116-14-67, authorization to transfer n° 2016-27-99). Fecal samples, plasma samples and clinical data will be collected from patients diagnosed with PXE who will be monitored at the Angers University Hospital Referral Center (France) in 2019-2020. Clinical severity of PXE will be assessed using modified Phenodex score. Gut microbiota will be analyzed using metagenomic sequencing. Plasma Vitamin K species and fecal excretion of menaquinones will be assessed using HPLC. Plasma dp-ucMGP (circulating biomarker of vitamin K status) and serum PIVKA-II (protein induced by vitamin K absence-II) will be assessed using immunoassay. Results will be compared to healthy age- and gender-matched controls from the pre-existing Biofortis database.
This study aims to demonstrate a potential association between gut microbiota composition, plasma levels of various forms of vitamin K, and severity of clinical manifestations of Pseudoxanthoma Elasticum (PXE).