Variegate porphyria: identification of a nonsense mutation in the protoporphyrinogen oxidase gene

A boy with blistering of sun-exposed skin and finger shortening: the first case of Variegate Porphyria with a novel mutation in protoporphyrinogen oxidase (PPOX) gene in Iran: a case report and literature review

Variegate Porphyria (VP) is an inherited rare disorder that is caused by mutations in the protoporphyrinogen oxidase (PPOX) gene. This deficiency is associated with the accumulation of porphyrins and porphyrin precursors in the body, which, in turn, can potentially result in a variety of skin and neurological symptoms. Here, we reported a 7-year-old boy with homozygous VP and novel mutation on PPOX gene. He was admitted with three episodes of generalized tonic-clonic seizure in the last 6 months. He was presented with lesions, hyperpigmentation, fragility, and blistering of sun-exposed skin. The weakness of limbs and brachydactyly were observed. In the follow-up, he had aggressive behavior, learning disability and abdominal pain, particularly around the navel. Eventually, the whole exome sequencing (WES) result reported a novel homozygous pathogenic variant (c.1072G > A p.G358R) in PPOX gene which confirmed the VP. He had been advised to be away from the sun and use sunscreen regularly.

Clinical and biochemical characteristics and genotype-phenotype correlation in Finnish variegate porphyria patients

Variegate porphyria (VP) is an inherited metabolic disease resulting from the partial deficiency of protoporphyrinogen oxidase, the penultimate enzyme in the heme biosynthetic pathway. We have evaluated the clinical and biochemical outcome of 103 Finnish VP patients diagnosed between 1966 and 2001. Fifty-two per cent of patients had experienced clinical symptoms: 40% had photosensitivity, 27% acute attacks and 14% both manifestations. The proportion of patients with acute attacks has decreased dramatically from 38 to 14% in patients diagnosed before and after 1980, whereas the prevalence of skin symptoms had decreased only subtly from 45 to 34%. We have studied the correlation between PPOX genotype and clinical outcome of 90 patients with the three most common Finnish mutations I12T, R152C and 338G-->C. The patients with the I12T mutation experienced no photosensitivity and acute attacks were rare (8%). Therefore, the occurrence of photosensitivity was lower in the I12T group compared to the R152C group (P=0.001), whereas no significant differences between the R152C and 338G-->C groups could be observed. Biochemical abnormalities were significantly milder suggesting a milder form of the disease in patients with the I12T mutation. In all VP patients, normal excretion of protoporphyrin in faeces in adulthood predicted freedom from both skin symptoms and acute attacks. The most valuable test predicting an increased risk of symptoms was urinary coproporphyrin, but only a substantially increased excretion exceeding 1,000 nmol/day was associated with an increased risk of both skin symptoms and acute attacks. All patients with an excretion of more than 1,000 nmol/day experienced either skin symptoms, acute attacks, or both.

Identification of a founder mutation in the protoporphyrinogen oxidase gene in variegate porphyria patients from chile

Variegate porphyria (VP; OMIM 176200) is characterized by a partial defect in the activity of protoporphyrinogen oxidase (PPO), the seventh enzyme of the porphyrin-heme biosynthetic pathway. The disease is usually inherited as an autosomal dominant trait displaying incomplete penetrance. In an effort to characterize the spectrum of molecular defects in VP, we identified 3 distinct mutations in 6 VP families from Chile by PCR, heteroduplex analysis, automated sequencing, restriction enzyme digestion and haplotyping analysis. The mutations consisted of 2 deletions and 1 missense mutation, designated 1239delTACAC, 1330delT and R168H. The occurrence of the missense mutation R168H had been reported previously in American, German and Dutch VP families, suggesting that this may represent a frequent recurrent mutation. Interestingly, the mutation 1239delTACAC was found in patients from 4 unrelated families living in different parts of Chile, suggesting that it might represent a common mutation in Chile. Haplotype analysis using 15 microsatellite markers which closely flank the PPO gene on chromosome 1q22, spanning approximately 21 cM, revealed the presence of R168H on different haplotypes in 6 VP patients from 3 unrelated families. In contrast, we found the occurrence of 1239delTACAC on the same chromosome 1 haplotype in 11 mutation carriers from 4 unrelated families with VP. These findings are consistent with R168H representing a hotspot mutation and 1239delTACAC existing as a founder mutation in the PPO gene. Our data comprise the first genetic studies of the porphyrias in South America and will streamline the elucidation of the genetic defects in VP patients from Chile by allowing an initial screening for the founder mutation 1239delTACAC.

Diagnosis of variegate porphyria--hard to get?

Variegate porphyria (VP) is an inherited metabolic disease that results from the partial deficiency of protoporphyrinogen oxidase. In this communication we have used DNA technology in the diagnosis of VP and compared the results with the biochemical and clinical data. To date, we have diagnosed 107 VP patients using either biochemical or DNA techniques or both. In addition, in 106 family members the diagnosis of VP could be excluded. The sensitivity and specificity of the biochemical screening for VP were studied among 38 family members. These individuals were either asymptomatic (n = 19) or had experienced occasional skin symptoms (n = 13), acute attacks (n = 5) or both (n = 1). The sensitivity of urinary and fecal coproporphyrin analysis was 48% and 52%, respectively. The sensitivity of urinary uroporphyrin analysis was 71% and for fecal protoporphyrin 77%. Plasma fluorescence was sensitive in symptomatic patients even in remission, but resulted in false negatives in four asymptomatic patients with normal excretion of porphyrins in the urine. In our series of mutation screening, many new asymptomatic patients were identified, and this demonstrated that DNA analysis is the only reliable way to screen (a)symptomatic patients facilitating correct treatment and proper genetic counselling of family members at risk. Biochemical analyses (e.g. plasma fluorescence, fecal protoporphyrins, urinary copro- and uroporphyrins, porphobilinogen and delta-aminolevulinic acid) are essential when the diagnosis of VP is confirmed at the symptomatic phase.

The cutaneous porphyrias

Deficiencies of 7 enzymes in the heme biosynthetic pathway result in the development of porphyrias. Two of the porphyrias, aminolevulinate dehydratase deficiency porphyria and acute intermittent porphyria do not have cutaneous findings. Cutaneous findings in the other porphyrias could be subdivided into acute phototoxicity and subacute phototoxicity. In addition, 2 of the porphyrias, hereditary coproporphyria and variegate porphyria have both cutaneous and neurovisceral findings. Now that chromosomal assignments for all the genes of the defective enzymes have been mode, prenatal diagnosis is possible for congenital erythropoietic porphyria, and in vitro gene therapy has been successfully performed for congenital erythropoietic porphyria and erythropoietic protoporphyria.

Variegate porphyria in Western Europe: identification of PPOX gene mutations in 104 families, extent of allelic heterogeneity, and absence of correlation between phenotype and type of mutation

Variegate porphyria (VP) is a low-penetrance, autosomal dominant disorder characterized clinically by skin lesions and acute neurovisceral attacks that occur separately or together. It results from partial deficiency of protoporphyrinogen oxidase encoded by the PPOX gene. VP is relatively common in South Africa, where most patients have inherited the same mutation in the PPOX gene from a common ancestor, but few families from elsewhere have been studied. Here we describe the molecular basis and clinical features of 108 unrelated patients from France and the United Kingdom. Mutations in the PPOX gene were identified by a combination of screening (denaturing gradient gel electrophoresis, heteroduplex analysis, or denaturing high-performance liquid chromatography) and direct automated sequencing of amplified genomic DNA. A total of 60 novel and 6 previously reported mutations (25 missense, 24 frameshift, 10 splice site, and 7 nonsense) were identified in 104 (96%) of these unrelated patients, together with 3 previously unrecognized single-nucleotide polymorphisms. VP is less heterogeneous than other acute porphyrias; 5 mutations were present in 28 (26%) of the families, whereas 47 mutations were restricted to 1 family; only 2 mutations were found in both countries. The pattern of clinical presentation was identical to that reported from South Africa and was not influenced by type of mutation. Our results define the molecular genetics of VP in western Europe, demonstrate its allelic heterogeneity outside South Africa, and show that genotype is not a significant determinant of mode of presentation.

Molecular characterization of homozygous variegate porphyria

Variegate porphyria (VP) is a low penetrance, autosomal dominant disorder that results from partial deficiency of protoporphyrinogen oxidase (PPOX) activity caused by mutation in the PPOX gene. The rare homozygous variant of VP is characterized by severe PPOX deficiency, onset of photosensitization by porphyrins in early childhood, skeletal abnormalities of the hand and, less constantly, short stature, mental retardation and convulsions. We have identified PPOX mutations on both alleles of five of the 11 unrelated patients with homozygous VP reported to date. Two patients were homoallelic for missense mutations (D349A and A433P), while three were heteroallelic. Functional analysis by prokaryotic expression showed that the D349A and A433P and one missense mutation in each of the three heteroallelic patients (G358R in two patients and A219KANA) preserved some PPOX activity (9.5-25% of wild-type). Mutations on the other allele of the heteroallelic patients abolished or markedly decreased activity. There was no relation between genotype assessed by functional analysis and the presence or severity of non-cutaneous manifestations. The mutations were absent from 104 unrelated patients with autosomal dominant VP. Our findings define the molecular pathology of homozygous VP and suggest that mild PPOX mutations occur in the general population but have very low or no clinical penetrance in heterozygotes.

Homozygous variegate porphyria: identification of mutations on both alleles of the protoporphyrinogen oxidase gene in a severely affected proband

Homozygous variegate porphyria is a severe skin and neurologic disease manifesting in early infancy, and characterized by markedly reduced levels of the penultimate enzyme in the heme biosynthetic pathway, protoporphyrinogen oxidase. We investigated the molecular basis of variegate porphyria, usually an autosomal dominantly inherited trait, in a severely affected female proband and her parents. The mutation detection strategy included heteroduplex analysis, automated sequencing, and allele specific oligonucleotide hybridization. We identified two underlying missense mutations in the protoporphyrinogen oxidase gene, consisting of a G-to-A transition in exon 6 (G169E), and a G-to-A transition in exon 10 (G358R). Our study establishes the molecular basis of "homozygous" variegate porphyria for the first time, in demonstrating that this patient is a compound heterozygote for two different missense mutations in the protoporphyrinogen oxidase gene.