Best practice guidelines on first-line laboratory testing for porphyria.

The porphyrias are disorders of haem biosynthesis which present with acute neurovisceral attacks or disorders of sun-exposed skin. Acute attacks occur mainly in adults and comprise severe abdominal pain, nausea, vomiting, autonomic disturbance, central nervous system involvement and peripheral motor neuropathy. Cutaneous porphyrias can be acute or chronic presenting at various ages. Timely diagnosis depends on clinical suspicion leading to referral of appropriate samples for screening by reliable biochemical methods. All samples should be protected from light. Investigation for an acute attack: • Porphobilinogen (PBG) quantitation in a random urine sample collected during symptoms. Urine concentration must be assessed by measuring creatinine, and a repeat requested if urine creatinine <2 mmol/L. • Urgent porphobilinogen testing should be available within 24 h of sample receipt at the local laboratory. Urine porphyrin excretion (TUP) should subsequently be measured on this urine. • Urine porphobilinogen should be measured using a validated quantitative ion-exchange resin-based method or LC-MS. • Increased urine porphobilinogen excretion requires confirmatory testing and clinical advice from the National Acute Porphyria Service. • Identification of individual acute porphyrias requires analysis of urine, plasma and faecal porphyrins. Investigation for cutaneous porphyria: • An EDTA blood sample for plasma porphyrin fluorescence emission spectroscopy and random urine sample for TUP. • Whole blood for porphyrin analysis is essential to identify protoporphyria. • Faeces need only be collected, if first-line tests are positive or if clinical symptoms persist. Investigation for latent porphyria or family history: • Contact a specialist porphyria laboratory for advice. Clinical, family details are usually required.

Congenital erythropoietic porphyria with two mutations of the uroporphyrinogen III synthase gene (Cys73Arg, Thr228Met).

Congenital erythropoietic porphyria (CEP) is an autosomal recessive inborn error of metabolism that results from the markedly deficient activity of uroporphyrinogen III synthase (UROS). We describe a 14-year-old girl with red urine since infancy, progressive blistering and scarring of the skin, and moderate hemolytic anemia. After years of skin damage, her face is mutilated; she has a bald patch on the scalp, hypertrichosis of the neck, areas of skin darkening, and limited joint movements of the hands. Total urine excretion and fecal total porphyrin were both markedly raised above normal levels. Sequencing of the UROS gene identified two mutations causing CEP (Cys73Arg, Thr228Met). The patient lesions are progressing. Bone marrow transplantation and/or gene therapy are proposed as the next steps in her treatment. In brief, we describe a CEP with confirmed two pathogenic mutations, severe phenotype and discuss the various treatment options available.

Diagnostic strategies for autosomal dominant acute porphyrias: retrospective analysis of 467 unrelated patients referred for mutational analysis of the HMBS, CPOX, or PPOX gene.

BACKGROUND: Clinically indistinguishable attacks of acute porphyria occur in acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP). There are few evidence-based diagnostic strategies for these disorders. METHODS: The diagnostic sensitivity of mutation detection was determined by sequencing and gene-dosage analysis to search for mutations in 467 sequentially referred, unrelated patients. The diagnostic accuracy of plasma fluorescence scanning, fecal porphyrin analysis, and porphobilinogen deaminase (PBGD) assay was assessed in mutation-positive patients (AIP, 260 patients; VP, 152 patients; HCP, 31 patients). RESULTS: Sensitivities (95% CI) for mutation detection were as follows: AIP, 98.1% (95.6%-99.2%); HCP, 96.9% (84.3%-99.5%); VP, 100% (95.7%-100%). We identified 5 large deletions in the HMBS gene (hydroxymethylbilane synthase) and one in the CPOX gene (coproporphyrinogen oxidase). The plasma fluorescence scan was positive more often in VP (99% of patients) than in AIP (68%) or HCP (29%). The wavelength of the fluorescence emission peak and the fecal coproporphyrin isomer ratio had high diagnostic specificity and sensitivity for differentiating between AIP, HCP, and VP. DNA analysis followed by PBGD assay in mutation-negative patients had greater diagnostic accuracy for AIP than either test alone. CONCLUSIONS: When PBG excretion is increased, 2 investigations (plasma fluorescence scanning, the coproporphyrin isomer ratio) are sufficient, with rare exceptions, to identify the type of acute porphyria. When the results of PBG, 5-aminolevulinate, and porphyrin analyses are within reference intervals and clinical suspicion that a past illness was caused by an acute porphyria remains high, mutation analysis of the HMBS gene followed by PBGD assay is an effective strategy for diagnosis or exclusion of AIP.