Molecular heterogeneity of familial porphyria cutanea tarda in Spain: characterization of 10 novel mutations in the UROD gene

Photosensitivity disorders in children: part I

Photosensitivity disorders in children encompass a diverse group of diseases. Compared to adult patients, underlying systemic disorders, including genetic or metabolic defects, are common causes in pediatric photosensitivity disorders. Photosensitivity in a child should be suspected if the child develops a sunburn reaction in sun-exposed sites after limited sun exposure. Diagnosis of a photodermatosis is made based on careful history taking and a physical examination. Early recognition and prompt diagnosis are essential to minimize long-term complications associated with inadequate photoprotection. In part I of this continuing medical education article, immunologically mediated photodermatoses, photodermatoses caused by exogenous photosensitizers, and the cutaneous porphyrias will be covered.

Molecular analysis of the UROD gene in 17 Argentinean patients with familial porphyria cutanea tarda: characterization of four novel mutations

Porphyria cutanea tarda (PCT) is caused by decreased activity of uroporphyrinogen decarboxylase (UROD) in the liver. The disease usually occurs in adulthood and is characterized by cutaneous photosensitivity, hyperpigmentation, skin fragility and hypertrichosis, due to the accumulation of porphyrins produced by oxidation of uroporphyrinogen and other highly carboxylated porphyrinogens overproduced as a result of the enzyme deficiency. PCT is generally sporadic, but about 20-30% of patients have familial-PCT (F-PCT) which is associated with heterozygosity of mutations in the UROD gene. In the present study we have found the molecular defect in seventeen unrelated Argentinean patients with F-PCT, identifying a total of eleven UROD gene mutations: four novel and seven previously described. The novel mutations were: a guanine insertion at the 5' splice junction of intron 2, a three nucleotide deletion causing the lost of valine 90, a deletion of 22 bp in exon 6 and a deletion of part of the polyadenylation signal. Prokaryotic expression studies showed that the novel amino acid deletion resulted in an inactive protein. Mutations c.10insA and p.M165R, previously found in Argentinean patients, were recurrent in this study; they are the most frequent in Argentina accounting for 40% of the mutant alleles characterized to date.

Identification and characterization of novel uroporphyrinogen decarboxylase gene mutations in a large series of porphyria cutanea tarda patients and relatives

Porphyria cutanea tarda (PCT) arises from decreased hepatic activity of uroporphyrinogen decarboxylase (UROD). Both genetic and environmental factors interplay in the precipitation of clinically overt PCT, but these factors may vary between different geographic areas. Decreased activity of UROD in erythrocytes was used to identify patients with UROD mutations among a group of 130 Spanish PCT patients. Nineteen patients (14.6%) were found to harbor a mutation in the UROD gene. Eight mutations were novel: M1I, 5del10, A22V, D79N, F84I, Q116X, T141I and Y182C. Five others were previously described: F46L, V134Q, R142Q, P150L and E218G. The new missense mutations and P150L were expressed in Escherichia coli. D79N and P150L resulted in proteins that were localized to inclusion bodies. The other mutations produced recombinant proteins that were purified and showed reduced activity (range: 2.3-73.2% of wild type). These single amino acid changes were predicted to produce complex structural alterations and/or reduced stability of the enzyme. Screening of relatives of the probands showed that 37.5% of mutation carriers demonstrated increased urinary porphyrins. This study emphasizes the role of UROD mutations as a strong risk factor for PCT even in areas where environmental factors (hepatitis C virus) have been shown to be highly associated with the disease.

Familial and Sporadic Porphyria Cutanea Tarda: Characterization and Diagnostic Strategies

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.