title: [Xanthinuria type 1 in a woman with arthralgias: a combined clinical and molecular genetic investigation].
abstract: METHODS
  A 53-year old woman with recurrent polyarthralgias, negative test results in a recent rheumatologic work-up and an unmeasurably low uric acid serum concentration presented for suspected IgM paraproteinemia.
  
  
  METHODS
  Physical examination, abdominal ultrasound and routine laboratory test results were unremarkable. Repeat determination confirmed a markedly decreased uric acid (UA) serum concentration. Urinary xanthine and hypoxanthine concentrations were increased by 14-fold and 7.5-fold, respectively. Fractional urinary UA excretion was not increased and the allopurinol loading test was normal. Sequencing of the xanthine dehydrogenase (XDH) gene revealed the pathogenic deletion c.641delC in the homozygous state. Segregation analysis showed that the patient's mother and her two adult sons were carriers of the mutation but not a half-sister and a half-brother of her deceased father. There was no evidence of parental consanguinity. These results established xanthinuria type 1 as the cause of the patient's recurrent polyarthralgias due to a previously unreported homozygosity for the known mutation c.641delC of the XDH gene.
  
  
  METHODS
  The patient was advised to adhere to a low-purine diet and to ensure an increased daily fluid-intake of at least 2.5 l. She has since remained symptom free.
  
  
  CONCLUSIONS
  Markedly lowered serum uric acid concentrations are a hallmark of xanthinuria and of hereditary renal hypouricemia, and in the absence of severe hepatic failure or evidence of an untoward drug effect should raise suspicion of these diseases. A targeted diagnostic work-up should then be initiated and factitious hypouricemia due to IgM paraproteinemia considered only in the case of equivocal test results. Molecular-genetic characterization and segregation analysis will ultimately establish the underlying genotype.
authors.forename: Roland Wolfgang
authors.initials: RW
authors.lastname: Därr
authors.forename: Steffen
authors.initials: S
authors.lastname: Lenzner
authors.forename: Thomas
authors.initials: T
authors.lastname: Eggermann
authors.forename: Wolfgang Hermann
authors.initials: WH
authors.lastname: Därr
mesh_terms: D018771:Arthralgia / Q000150:complications / Q000209:etiology; D005260:Female; D006801:Humans; D019271:Hypoxanthine / Q000652:urine; D008661:Metabolism, Inborn Errors / Q000150:complications / Q000175:diagnosis / Q000178:diet therapy / Q000235:genetics; D008875:Middle Aged; D019820:Xanthine / Q000652:urine; D014968:Xanthine Dehydrogenase / Q000172:deficiency* / Q000235:genetics
chemical_list: D019820:Xanthine; D019271:Hypoxanthine; D014968:Xanthine Dehydrogenase