Unravelling 5-oxoprolinuria (pyroglutamic aciduria) due to bi-allelic OPLAH mutations: 20 new mutations in 14 families

Abstract

Primary 5-oxoprolinuria (pyroglutamic aciduria) is caused by a genetic defect in the γ-glutamyl cycle, affecting either glutathione synthetase or 5-oxoprolinase. While several dozens of patients with glutathione synthetase deficiency have been reported, with hemolytic anemia representing the clinical key feature, 5-oxoprolinase deficiency due to OPLAH mutations is less frequent and so far has not attracted much attention. This has prompted us to investigate the clinical phenotype as well as the underlying genotype in patients from 14 families of various ethnic backgrounds who underwent diagnostic mutation analysis following the detection of 5-oxoprolinuria. In all patients with 5-oxoprolinuria studied, bi-allelic mutations in OPLAH were indicated. An autosomal recessive mode of inheritance for 5-oxoprolinase deficiency is further supported by the identification of a single mutation in all 9/14 parent sample sets investigated (except for the father of one patient whose result suggests homozygosity), and the absence of 5-oxoprolinuria in all tested heterozygotes. It is remarkable, that all 20 mutations identified were novel and private to the respective families. Clinical features were highly variable and in several sib pairs, did not segregate with 5-oxoprolinuria. Although a pathogenic role of 5-oxoprolinase deficiency remains possible, this is not supported by our findings. Additional patient ascertainment and long-term follow-up is needed to establish the benign nature of this inborn error of metabolism. It is important that all symptomatic patients with persistently elevated levels of 5-oxoproline and no obvious explanation are investigated for the genetic etiology.

Discovery of a widespread prokaryotic 5-oxoprolinase that was hiding in plain sight

“…Its reported effects include growth inhibition in prokaryotes and plants (10,15) and interference with energy production, lipid synthesis, and antioxidant defenses in mammalian brain (16,17). Human inborn errors of glutathione metabolism that lead to OP buildup result in metabolic acidosis, hemolytic anemia, neurological problems, and massive urinary excretion of OP (18,19).…”

Catalytic and structural properties of ATP‐dependent caprolactamase from Pseudomonas jessenii

“…The proteins were upregulated in cells growing on caprolactam as compared to cells cultivated on glucose. Among known proteins with confirmed activity, the closest homologs of caprolactamase are eukaryotic oxoprolinases (OP), 6 for example the human, bovine and rat enzymes and the oxoprolinase from Saccharomyces cerevisiae 26–29 . These are dimeric enzymes with subunits of around 1250 amino acids.…”

Uncovering Missing Heritability in Rare Diseases

“…Newly discovered genetic conditions may also co-occur with another genetic condition(s) [28,29] (e.g., NPL and GJB2 composite effects in a patient with sialuria, exercise intolerance/muscle wasting, cardiac symptoms, and deafness) [28]. Thus, considering multiple diagnoses in a patient is important in presumed monogenic disorders, especially the ones with atypical ‘ultra’ rare phenotypes [30] and/or substantial phenotypic variability [31] before a conclusion on expanded clinical presentation of a monogenic disease is made.…”