The pathogenic c.1171A>G (p.Arg391Gly) and c.2359G>A (p.Val787Ile) ABCC6 variants display incomplete penetrance causing pseudoxanthoma elasticum in a subset of individuals.

"CONFLICT OF INTEREST The authors declare no conflict of interest."

"Authors gratefully acknowledge the collaboration of people affected by PXE and the support of PXE International and other patient associations. This work is a result of a collaboration in the frame of the EuroSoftCalcNet COST Action (CA16‐115). This work was supported by the National Research, Development and Innovation Office (NKFIH, FK131946), U.S Department of State (Fulbright Visiting Scholar Program), Hungarian Academy of Sciences (Bolyai Janos Fellowship BO/00730/19/8, Mobility grant) and by the UNKP‐2021, UNKP‐2022 New National Excellence Program of the Ministry for Innovation and Technology from the source of the NKFIH to Flora Szeri. Further funding for this work was provided by PXE International and the NIH NIAMS Grant R01AR072695 (KvdW, QL, and JU), PXE Italia Odv (DQ). Shana Verschuere is a PhD Fellow supported by a Methusalem grant from the Ghent University ‐ Belgium (BOF08/01M01108). Olivier M. Vanakker is a Senior Clinical Investigator of the Research Foundation Flanders (FWO)—Belgium. MTA‐SE Lendulet Research Grant (LP2015‐11/2015) of the Hungarian Academy of Sciences, the KH125566, K135798 grants to Kalman Tory and the Ministry of Human Capacities in Hungary in the frame of Institutional Excellence Program for Higher Education. Diagnosis and management of PXE DNA samples occurred at the PXE Reference Center (MAGEC Nord), Angers University Hospital, Angers, France, as a part of the French PXE cohort (ClinicalTrials.gov Identifier: NCT01446380). Tamas Aranyi is a beneficiary of the NKFIH K132695 grant."