title: Familial and sporadic porphyria cutanea tarda: characterization and diagnostic strategies.
abstract: BACKGROUND
  Porphyria cutanea tarda (PCT) occurs in sporadic (sPCT) and familial (fPCT) forms, which are generally clinically indistinguishable and have traditionally been differentiated by erythrocyte uroporphyrinogen decarboxylase (UROD, EC 4.1.1.37) activity. We used UROD gene sequencing as the reference standard in assessing the diagnostic accuracy of UROD activity, evaluating the mutation spectrum of the UROD gene, determining the frequency and disease attributes of PCT and its subtypes in Norway, and developing diagnostic models that use clinical and laboratory characteristics for differentiating fPCT and sPCT.
  
  
  METHODS
  All consecutive patients with PCT diagnosed within a 6-year period were used for incidence calculations. UROD activity analysis, UROD gene sequencing, analysis of hemochromatosis mutations, and registration of clinical and laboratory data were carried out for 253 patients.
  
  
  RESULTS
  Fifty-three percent of the patients had disease-relevant mutations, 74% of which were c.578G>C or c.636+1G>C. The UROD activity at the optimal cutoff had a likelihood ratio (LR) of 9.2 for fPCT, whereas a positive family history had an LR of 19. A logistic regression model indicated that low UROD activity, a high uroporphyrin-heptaporphyrin ratio, a young age at diagnosis, male sex, and low alcohol consumption were predictors of fPCT. The incidence of PCT was 1 in 100 000.
  
  
  CONCLUSIONS
  Two commonly occurring mutations are responsible for the high frequency of fPCT in Norway. UROD activity has a high diagnostic accuracy for differentiating the 2 PCT types, and a model that takes into account both clinical information and laboratory test results can be used to predict fPCT.
authors.affiliation: Norwegian Porphyria Centre (NAPOS), Laboratory of Clinical Biochemistry, Haukeland University Hospital, Bergen, Norway. aasne.aarsand@helse-bergen.no
authors.forename: Aasne K
authors.initials: AK
authors.lastname: Aarsand
authors.forename: Helge
authors.initials: H
authors.lastname: Boman
authors.forename: Sverre
authors.initials: S
authors.lastname: Sandberg
mesh_terms: D001483:Base Sequence; D005260:Female; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000235:genetics*; D005838:Genotype; D000071020:Hemochromatosis Protein; D015395:Histocompatibility Antigens Class I / Q000235:genetics; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D008875:Middle Aged; D009154:Mutation / Q000235:genetics; D017119:Porphyria Cutanea Tarda / Q000175:diagnosis* / Q000453:epidemiology / Q000235:genetics* / Q000378:metabolism; D014575:Uroporphyrinogen Decarboxylase / Q000235:genetics / Q000378:metabolism
chemical_list: C103673:HFE protein, human; D000071020:Hemochromatosis Protein; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D014575:Uroporphyrinogen Decarboxylase