title: Diagnostic Value of Urinary Mevalonic Acid Excretion in Patients with a Clinical Suspicion of Mevalonate Kinase Deficiency (MKD).
abstract: OBJECTIVE
  In patients suffering from mevalonate kinase deficiency (MKD), the reduced enzyme activity leads to an accumulation of mevalonic acid which is excreted in the urine. This study aims to evaluate the diagnostic value of urinary mevalonic acid measurement in patients with a clinical suspicion of mevalonate kinase deficiency.
  
  
  METHODS
  In this single-center, retrospective analysis, all patients in whom both measurement of mevalonic acid and genetic testing had been performed in the preceding 17 years have been included. The presence of two pathogenic MVK mutations or demonstration of decreased enzyme activity was considered to be the gold standard for the diagnosis of MKD.
  
  
  RESULTS
  Sixty-one patients were included in this study. Thirteen of them harbored two MVK mutations; twelve of them showed elevated levels of mevalonic acid. Forty-eight patients did not harbor any MVK mutations, yet five of them excreted increased amounts of mevalonic acid. This corresponds to a sensitivity of 92%, a specificity of 90%, a positive predictive value of 71%, and a negative predictive value of 98%. The positive likelihood ratio is 10 and the negative likelihood ratio is 0.09.
  
  
  CONCLUSIONS
  MKD seems very unlikely in patients with a normal mevalonic acid excretion, but it cannot be excluded completely. Further, a positive urinary mevalonic acid excretion still requires MVK analysis to confirm the diagnosis of MKD. Therefore, detection of urinary mevalonic acid should not be mandatory before genetic testing. However, as long as genetic testing is not widely available and affordable, measurement of urinary mevalonic acid is a fair way to select patients for MVK gene analysis or enzyme assay.
authors.affiliation: Department of Pediatrics, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Jerold
authors.initials: J
authors.lastname: Jeyaratnam
authors.affiliation: Laboratory of Translational Immunology, University Medical Center Utrecht, Utrecht, The Netherlands. n.m.terhaar-2@umcutrecht.nl.
authors.forename: Nienke M
authors.initials: NM
authors.lastname: Ter Haar
authors.affiliation: Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Monique G M
authors.initials: MG
authors.lastname: de Sain-van der Velden
authors.affiliation: Clinical Chemistry and Pediatrics, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Hans R
authors.initials: HR
authors.lastname: Waterham
authors.affiliation: Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Mariëlle E
authors.initials: ME
authors.lastname: van Gijn
authors.affiliation: Department of Pediatrics, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Joost
authors.initials: J
authors.lastname: Frenkel