PPA1 Deficiency Causes a Deranged Galactose Metabolism Recognizable in Neonatal Screening
Melanie T. Achleitner,
Judith J. M. Jans,
Laura Ebner,
Johannes Spenger,
Vassiliki Konstantopoulou,
René G. Feichtinger,
Karin Brugger,
Doris Mayr,
Ron A. Wevers,
Christian Thiel,
Saskia B. Wortmann,
Johannes A. Mayr
Affiliations
Melanie T. Achleitner
University Children’s Hospital, Salzburger Landeskliniken (SALK), Paracelsus Medical University, 5020 Salzburg, Austria
Judith J. M. Jans
Department of Genetics, University Medical Center Utrecht, Utrecht University, 3584 CX Utrecht, The Netherlands
Laura Ebner
University Children’s Hospital, Salzburger Landeskliniken (SALK), Paracelsus Medical University, 5020 Salzburg, Austria
Johannes Spenger
University Children’s Hospital, Salzburger Landeskliniken (SALK), Paracelsus Medical University, 5020 Salzburg, Austria
Vassiliki Konstantopoulou
Department of Pediatrics, Austrian Newborn Screening, Medical University of Vienna, 1090 Vienna, Austria
René G. Feichtinger
University Children’s Hospital, Salzburger Landeskliniken (SALK), Paracelsus Medical University, 5020 Salzburg, Austria
Karin Brugger
University Children’s Hospital, Salzburger Landeskliniken (SALK), Paracelsus Medical University, 5020 Salzburg, Austria
Doris Mayr
University Children’s Hospital, Salzburger Landeskliniken (SALK), Paracelsus Medical University, 5020 Salzburg, Austria
Ron A. Wevers
Department of Human Genetics, Translational Metabolic Laboratory, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands
Christian Thiel
Center for Child and Adolescent Medicine, Pediatrics I, University Heidelberg, Analysezentrum 3, 69120 Heidelberg, Germany
Saskia B. Wortmann
University Children’s Hospital, Salzburger Landeskliniken (SALK), Paracelsus Medical University, 5020 Salzburg, Austria
Johannes A. Mayr
University Children’s Hospital, Salzburger Landeskliniken (SALK), Paracelsus Medical University, 5020 Salzburg, Austria
Two siblings showed increased galactose and galactose-related metabolites in neonatal screening. Diagnostic workup did not reveal abnormalities in any of the known disease-causing enzymes involved in galactose metabolism. Using whole-exome sequencing, we identified a homozygous missense variant in PPA1 encoding the cytosolic pyrophosphatase 1 (PPA1), c.557C>T (p.Thr186Ile). The enzyme activity of PPA1 was determined using a colorimetric assay, and the protein content was visualized via western blotting in skin fibroblasts from one of the affected individuals. The galactolytic activity of the affected fibroblasts was determined by measuring extracellular acidification with a Seahorse XFe96 analyzer. PPA1 activity decreased to 22% of that of controls in the cytosolic fraction of homogenates from patient fibroblasts. PPA1 protein content decreased by 50% according to western blot analysis, indicating a reduced stability of the variant protein. The extracellular acidification rate was reduced in patient fibroblasts when galactose was used as a substrate. Untargeted metabolomics of blood samples revealed an elevation of other metabolites related to pyrophosphate metabolism. Besides hyperbilirubinemia in the neonatal period in one child, both children were clinically unremarkable at the ages of 3 and 14 years, respectively. We hypothesize that the observed metabolic derangement is a possible mild manifestation of PPA1 deficiency. Unresolved abnormalities in galactosemia screening might result in the identification of more individuals with PPA1 deficiency, a newly discovered inborn metabolic disorder (IMD).
