European Specialist Porphyria Laboratories: Diagnostic Strategies, Analytical Quality, Clinical Interpretation, and Reporting As Assessed by an External Quality Assurance Program

BACKGROUND

The porphyrias are a group of rare metabolic disorders whose diagnosis depends on identification of specific patterns of porphyrin precursor and porphyrin accumulation in urine, blood, and feces. Diagnostic tests for porphyria are performed by specialized laboratories in many countries. Data regarding the analytical and diagnostic performance of these laboratories are scarce.

METHODS

We distributed 5 sets of multispecimen samples from different porphyria patients accompanied by clinical case histories to 18–21 European specialist porphyria laboratories/centers as part of a European Porphyria Network organized external analytical and postanalytical quality assessment (EQA) program. The laboratories stated which analyses they would normally have performed given the case histories and reported results of all porphyria-related analyses available, interpretative comments, and diagnoses.

RESULTS

Reported diagnostic strategies initially showed considerable diversity, but the number of laboratories applying adequate diagnostic strategies increased during the study period. We found an average interlaboratory CV of 50% (range 12%–152%) for analytes in absolute concentrations. Result normalization by forming ratios to the upper reference limits did not reduce this variation. Sixty-five percent of reported results were within biological variation–based analytical quality specifications. Clinical interpretation of the obtained analytical results was accurate, and most laboratories established the correct diagnosis in all distributions.

CONCLUSIONS

Based on a case-based EQA scheme, variations were apparent in analytical and diagnostic performance between European specialist porphyria laboratories. Our findings reinforce the use of EQA schemes as an essential tool to assess both analytical and diagnostic processes and thereby to improve patient care in rare diseases.

Protoporphyrin retention in hepatocytes and Kupffer cells prevents sclerosing cholangitis in erythropoietic protoporphyria mouse model

BACKGROUND & AIMS

Chronic, progressive hepatobiliary disease is the most severe complication of erythropoietic protoporphyria (EPP) and can require liver transplantation, although the mechanisms that lead to liver failure are unknown. We characterized protoporphyrin-IX (PPIX)-linked hepatobiliary disease in BALB/c and C57BL/6 (Fechm1Pas) mice with mutations in ferrochelatase as models for EPP.

METHODS

Fechm1Pas and wild-type (control) mice were studied at 12-14 weeks of age. PPIX was quantified; its distribution in the liver, serum levels of lipoprotein-X, liver histology, contents of bile salt and cholesterol phospholipids, and expression of genes were compared in mice of the BALB/c and C57BL/6 backgrounds. The in vitro binding affinity of PPIX for bile components was determined.

RESULTS

Compared with mice of the C57BL/6 background, BALB/c Fechm1Pas mice had a more severe pattern of cholestasis, fibrosis with portoportal bridging, bile acid regurgitation, sclerosing cholangitis, and hepatolithiasis. In C57BL/6 Fechm1Pas mice, PPIX was sequestrated mainly in the cytosol of hepatocytes and Kupffer cells, whereas, in BALB/c Fechm1Pas mice, PPIX was localized within enlarged bile canaliculi. Livers of C57BL/6 Fechm1Pas mice were protected through a combination of lower efflux of PPIX and reduced synthesis and export of bile acid.

CONCLUSIONS

PPIX binds to bile components and disrupts the physiologic equilibrium of phospholipids, bile acids, and cholesterol in bile. This process might be involved in pathogenesis of sclerosing cholangitis from EPP; a better understanding might improve diagnosis and development of reagents to treat or prevent liver failure in patients with EPP.

Sideroblastic anemia: molecular analysis of the ALAS2 gene in a series of 29 probands and functional studies of 10 missense mutations

X-linked Sideroblastic Anemia (XLSA) is the most common genetic form of sideroblastic anemia, a heterogeneous group of disorders characterized by iron deposits in the mitochondria of erythroid precursors. XLSA is due to mutations in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene. Thirteen different ALAS2 mutations were identified in 16 out of 29 probands with sideroblastic anemia. One third of the patients were females with a highly skewed X-chromosome inactivation. The identification of seven novel mutations in the ALAS2 gene, six missense mutations, and one deletion in the proximal promoter extends the allelic heterogeneity of XSLA. Most of the missense mutations were predicted to be deleterious, and 10 of them, without any published functional characterization, were expressed in Escherichia coli. ALAS2 activities were assayed in vitro. Five missense mutations resulted in decreased enzymatic activity under standard conditions, and two other mutated proteins had decreased activity when assayed in the absence of exogenous pyridoxal phosphate and increased thermosensitivity. Although most amino acid substitutions result in a clearly decreased enzymatic activity in vitro, a few mutations have a more subtle effect on the protein that is only revealed by in vitro tests under specific conditions.

A genetic schizophrenia-susceptibility region located between the ANKK1 and DRD2 genes

BACKGROUND

The gene coding for the D2 dopamine receptor (DRD2) is considered to be one of the most pertinent candidate genes in schizophrenia. However, genetic studies have yielded conflicting results whereas the promising TaqIA variant/rs1800497 has been mapped in a novel gene, ANKK1.

METHODS

We investigated eleven single nucleotide polymorphisms (SNPs) spanning the DRD2 and ANKK1 genes, using both a case-control association study comparing 144 independent patients to 142 matched healthy subjects, and a transmission disequilibrium test in 108 trios. This classical genetic study was coupled with a cladistic phylogeny-based association test of human variants, and with an interspecies evolution study of ANKK1.

RESULTS

Case-control study, followed by a 108 trios family-based association analysis for replication, revealed an association between schizophrenia and the ANKK1 rs1800497 (p=0.01, Odds Ratio=1.5, 95% Confidence Interval=1.1-2.2), and the intergenic rs2242592 (p=2.10(-4), OR=1.8, 95%CI=1.3-2.5). A significant SNP-SNP interaction was also found (p<10(-5), OR=2.0, 95%CI=1.6-2.5). The phylogeny-based association test also identified an association between both these polymorphisms and schizophrenia. Finally, interspecies comparison of the sequences from chimpanzee, orangutan, rhesus macaque and human species suggested specific involvement of ANKK1 in the human lineage.

CONCLUSIONS

Intergenic rs2242592 appears to be involved in the genetic vulnerability to schizophrenia, whereas the ANKK1 rs1800497 appears to have a modifying rather than causative effect. Finally, ANKK1 may be a specific human lineage-trait involved in a specific human disease, schizophrenia.

Porphyrias

Hereditary porphyrias are a group of eight metabolic disorders of the haem biosynthesis pathway that are characterised by acute neurovisceral symptoms, skin lesions, or both. Every porphyria is caused by abnormal function of a separate enzymatic step, resulting in a specific accumulation of haem precursors. Seven porphyrias are the result of a partial enzyme deficiency, and a gain of function mechanism has been characterised in a new porphyria. Acute porphyrias present with acute attacks, typically consisting of severe abdominal pain, nausea, constipation, confusion, and seizure, and can be life-threatening. Cutaneous porphyrias present with either acute painful photosensitivity or skin fragility and blisters. Rare recessive porphyrias usually manifest in early childhood with either severe cutaneous photosensitivity and chronic haemolysis or chronic neurological symptoms with or without photosensitivity. Porphyrias are still underdiagnosed, but when they are suspected, and dependent on clinical presentation, simple first-line tests can be used to establish the diagnosis in all symptomatic patients. Diagnosis is essential to enable specific treatments to be started as soon as possible. Screening of families to identify presymptomatic carriers is crucial to decrease risk of overt disease of acute porphyrias through counselling about avoidance of potential precipitants.

Erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is an inherited disorder of the haem metabolic pathway characterised by accumulation of protoporphyrin in blood, erythrocytes and tissues, and cutaneous manifestations of photosensitivity. EPP has been reported worldwide, with prevalence between 1:75,000 and 1:200,000. It usually manifests in early infancy upon the first sun exposures. EPP is characterised by cutaneous manifestations of acute painful photosensitivity with erythema and oedema, sometimes with petechiae, together with stinging and burning sensations upon exposure to sunlight, without blisters. These episodes have a variable severity depending on the exposure duration and may result in chronic permanent lesions on exposed skin. As protoporphyrin is a lipophilic molecule that is excreted by the liver, EPP patients are at risk of cholelithiasis with obstructive episodes, and chronic liver disease that might evolve to rapid acute liver failure. In most patients, EPP results from a partial deficiency of the last enzyme of the haem biosynthetic pathway, ferrochelatase, EC 4.99.1.1/FECH (encoded by the FECH gene). EPP appears to be inherited as an autosomal dominant disease, the clinical expression of which is modulated by the presence of the hypomorphic FECH IVS3-48C allele trans, but recessive inheritance with two mutated FECH alleles has also been described. In about 2% of patients, overt disease was recently shown to be caused by gain-of-function mutations in the erythroid-specific aminolevulinic acid synthase 2 (ALAS2/ALAS, EC 2.3.1.27) gene and named X-linked dominant protoporphyria. Diagnosis is established by finding increased levels of protoporphyrin in plasma and red blood cells, and detection of a plasma fluorescence peak at 634 nm. Investigations for hepatic involvement, ferrochelatase activity level, genetic analysis (FECH mutations, presence of the hypomorphic FECH IVS3-48C allele trans and ALAS2 mutations) and family studies are advisable. Differential diagnosis includes phototoxic drug reactions, hydroa vacciniforme, solar urticaria, contact dermatitis, angio-oedema and, in some cases, other types of porphyria. Management includes avoidance of exposure to light, reduction of protoporphyrin levels and prevention of progression of possible liver disease to liver failure. As the major risk in EPP patients is liver disease, a regular follow-up of hepatic involvement is essential. Sequential hepatic and bone marrow transplantation should be considered as a suitable treatment for most severe cases of EPP with hepatic involvement. EPP is a lifelong disorder whose prognosis depends on the evolution of the hepatic disease. However, photosensitivity may have a significant impact on quality of life of EPP patients.

Role of two nutritional hepatic markers (insulin-like growth factor 1 and transthyretin) in the clinical assessment and follow-up of acute intermittent porphyria patients

OBJECTIVE

Acute intermittent porphyria (AIP) is caused by a deficiency of hydroxymethylbilane synthase. Clinical manifestations are abdominal pain and neurovisceral symptoms, accompanied by overproduction of heme-precursors in the liver, which frequently remains long-lasting in AIP patients. We tested the hypothesis that this condition may be associated with alterations of hepatic proteins known to be either increased or decreased in serum according to diverse pathological conditions including malnutrition, inflammation or liver disease.

DESIGN

Serum proteins were analyzed in 26 biochemically active AIP patients that were classified according to the EPI (European Porphyria Initiative) guidelines as follows: (i) patients who presented a single acute attack having remained so far free of clinical symptoms; (ii) patients who present recurrent attacks or chronic symptoms associated with exacerbations of AIP.

RESULTS

Most of the serum proteins were within normal limits, however insulin-like growth factor 1 (IGF-1) was decreased in 53.8% of AIP patients (z-score = -2.86 +/- 0.37) and transthyretin (prealbumin) was found significantly decreased in 38.5% of them. The IGF-1 z-score was lower in group B versus group A patients (-2.66 vs. -1.43; P = 0.024). The coincident decrease of both IGF-1 and transthyretin was associated with worsening of the clinical condition.

CONCLUSIONS

This first study in humans suggests that the clinical expression AIP is associated with a state of under-nutrition and/or with hepatic inflammation due to the sustained accumulation of heme-precursors. We propose the use of both IGF-1 and transthyretin as biomarkers of disease morbidity/severity for the clinical follow-up of AIP patients.

Excessive erythrocyte PPIX influences the hematologic status and iron metabolism in patients with dominant erythropoietic protoporphyria

Partial deficiency of the last enzyme of the heme biosynthetic pathway (namely ferrochelatase, FECH) in humans is responsible for erythropoietic protoporphyria (EPP). This disorder is characterised by painful photosensitivity, due to excessive production of protoporphyrin IX (PPIX) by erythrocytes. Controversial hypotheses have been proposed to explain the hematologic and iron status of EPP patients. In the present work, we explored these parameters in 55 patients with dominant EPP recruited at the French Center of Porphyrias (Colombes, France) and confirmed by molecular analysis. Our data show that erythrocyte accumulation of PPIX in EPP patients influences hematologic and iron status. Patients studied had a mild anemia and thrombocytopenia, as shown by the downward shift of hematologic parameters, which positively correlated with the amount of erythrocyte PPIX. Interestingly, erythropoiesis did not seem to be limited by iron supply in patients, since serum iron and soluble transferring (Tf) receptor (sTfR) were normal. However, iron and Tf saturation negatively correlated with erythrocyte PPIX. Moreover, and as previously described in a mouse model of EPP, we noted a positive correlation between erythrocyte PPIX and Tf levels. Altogether, these results suggest a positive effect of PPIX on the synthesis on Tf, which could facilitate the mobilization of tissue iron stores to meet erythropoiesis requirement. Based on these observations and previous results in EPP mouse model, we propose that the PPIX-liver transferrin pathway plays a role in the orchestration of iron distribution between peripheral iron stores, the spleen and the bone marrow.

C-terminal deletions in the ALAS2 gene lead to gain of function and cause X-linked dominant protoporphyria without anemia or iron overload

All reported mutations in ALAS2, which encodes the rate-regulating enzyme of erythroid heme biosynthesis, cause X-linked sideroblastic anemia. We describe eight families with ALAS2 deletions, either c.1706-1709 delAGTG (p.E569GfsX24) or c.1699-1700 delAT (p.M567EfsX2), resulting in frameshifts that lead to replacement or deletion of the 19-20 C-terminal residues of the enzyme. Prokaryotic expression studies show that both mutations markedly increase ALAS2 activity. These gain-of-function mutations cause a previously unrecognized form of porphyria, X-linked dominant protoporphyria, characterized biochemically by a high proportion of zinc-protoporphyrin in erythrocytes, in which a mismatch between protoporphyrin production and the heme requirement of differentiating erythroid cells leads to overproduction of protoporphyrin in amounts sufficient to cause photosensitivity and liver disease.

The V249I polymorphism of the CX3CR1 gene is associated with fibrostenotic disease behavior in patients with Crohn's disease

OBJECTIVES

CX3CR1, the receptor of CX3CL1/fractalkine, is involved in regulation of inflammatory response and the CX3CR1-I249-M280 naturally occurring mutants are associated with altered binding to the ligand. Our aim was to evaluate the frequency of CX3CR1 V249I and T280M polymorphisms and NOD2/CARD15 mutations in Crohn's disease patients and to search for a relationship with phenotype.

METHODS

Clinical data were retrospectively collected. V249I and T280M polymorphisms of CX3CR1 gene and NOD2/CARD15 mutations (R702W, G908R, 3020InsC) were identified.

RESULTS

Two hundred and thirty-nine patients (140 females, 39.7+/-14.1 years) were included. About 37.4% were heterozygous and 8.8% were homozygous for the V249I CX3CR1 polymorphism, 18.1% were heterozygous and 1.3% homozygous for the T280M CX3CR1 polymorphism and 35.9% had at least one of the three mutations of NOD2/CARD15. The T280M CX3CR1 polymorphism was not associated with any phenotype. In univariate analysis, stenosis was significantly associated with both V249I CX3CR1 polymorphism and 3020InsC NOD2/CARD15 mutations. In smoker patients carrying the CX3CR1 allele I249, there was a significant increase in the frequency of fibrostenosing disease [P=0.005, odds ratio (OR): 3.25] whereas this relationship disappeared in the group of nonsmokers (P=0.72). In multivariate analysis, 3020InsC NOD2/CARD15 mutations and the V249I CX3CR1 polymorphism were independent risk factors for intestinal stenosis (P=0.046, OR: 1.8 and P=0.044, OR: 2.4, respectively).

CONCLUSION

In Crohn's disease, V249I CX3CR1 polymorphism is associated with intestinal strictures, particularly in smokers. This association is independent of CARD15 mutations.

Genetic study of variation in normal mouse iron homeostasis reveals ceruloplasmin as an HFE-hemochromatosis modifier gene

BACKGROUND & AIMS

Genetic hemochromatosis is one of the most common genetic disorders, with progressive tissue iron overload leading to severe clinical complications. In Northern European populations, genetic hemochromatosis is usually caused by homozygosity for the C282Y mutation in the HFE protein. However, penetrance of this mutation is incomplete, suggesting that other genetic and environmental factors contribute to its differential biologic or clinical expression.

METHODS

To identify genes modifying iron homeostasis, we screened the 27 recombinant congenic strains of the C3H/DiSnA-C57BL/10ScSnA/Dem series for tissue and serum iron indices and genotyped 18 microsatellite markers in (C3H/DiSnA x HcB-2) F2 hybrid mice.

RESULTS

We identified 1 locus encompassing the Ceruloplasmin (Cp) gene with a strong linkage with liver iron, serum iron, and transferrin levels but not with spleen iron. Sequencing of Cp showed an R435X nonsense mutation in exon 7 in C3H/DiSnA mice. To evaluate whether Cp might act as a modifier gene of genetic hemochromatosis, we intercrossed C3H Hfe(-/-) and C3HDiSnA Cp(R435X/R435X) mice. As expected, we found that double-mutant mice deposited more iron in the liver than mice defective for either one or both genes. In contrast, Hfe(-/-) x Cp(R435/R435X) or Cp(R435X/R435X) x Hfe(+/-) showed 30% decrease in liver iron when compared with single mutant mice.

CONCLUSIONS

This study highlights the existence of complex interactions between Cp and HFE and represents the first example of a modifier gene with a protective effect, in which heterozygosity reduces the iron load in the context of HFE deficiency.

Increased plasma transferrin, altered body iron distribution, and microcytic hypochromic anemia in ferrochelatase-deficient mice

Patients with deficiency in ferrochelatase (FECH), the last enzyme of the heme biosynthetic pathway, experience a painful type of skin photosensitivity called erythropoietic protoporphyria (EPP), which is caused by the excessive production of protoporphyrin IX (PPIX) by erythrocytes. Controversial results have been reported regarding hematologic status and iron status of patients with EPP. We thoroughly explored these parameters in Fechm1Pas mutant mice of 3 different genetic backgrounds. FECH deficiency induced microcytic hypochromic anemia without ringed sideroblasts, little or no hemolysis, and no erythroid hyperplasia. Serum iron, ferritin, hepcidin mRNA, and Dcytb levels were normal. The homozygous Fechm1Pas mutant involved no tissue iron deficiency but showed a clear-cut redistribution of iron stores from peripheral tissues to the spleen, with a concomitant 2- to 3-fold increase in transferrin expression at the mRNA and the protein levels. Erythrocyte PPIX levels strongly correlated with serum transferrin levels. At all stages of differentiation in our study, transferrin receptor expression in bone marrow erythroid cells in Fechm1Pas was normal in mutant mice but not in patients with iron-deficiency anemia. Based on these observations, we suggest that oral iron therapy is not the therapy of choice for patients with EPP and that the PPIX–liver transferrin pathway plays a role in the orchestration of iron distribution between peripheral iron stores, the spleen, and the bone marrow.

Biochemical compared to molecular diagnosis in acute intermittent porphyria

The biochemical and the molecular diagnoses of an inherited porphyria require experience. False positive or negative screening tests and the low penetrance of the disease make a correct diagnosis difficult.The biochemical and the molecular procedures for the diagnosis of acute intermittent porphyria were applied to five unrelated patients suffering from acute intermittent porphyria. All patients were shown to be gene carriers of acute intermittent porphyria by both methods. The two different possibilities of the diagnosis corresponded well. In a family definitively identified by molecular diagnosis of one of the patients and his relatives, the patient's two children were asymptomatic. His son was shown to be a gene carrier of the father's deficiency by biochemical as well as molecular analysis, whereas his daughter was not affected by acute intermittent porphyria.

Contribution of a common single-nucleotide polymorphism to the genetic predisposition for erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is an inherited disorder of heme biosynthesis that results from a partial deficiency of ferrochelatase (FECH). Recently, we have shown that the inheritance of the common hypomorphic IVS3-48C allele trans to a deleterious mutation reduces FECH activity to below a critical threshold and accounts for the photosensitivity seen in patients. Rare cases of autosomal recessive inheritance have been reported. We studied a cohort of 173 white French EPP families and a group of 360 unrelated healthy subjects from four ethnic groups. The prevalences of the recessive and dominant autosomal forms of EPP are 4% (95% confidence interval 1-8) and 95% (95% confidence interval 91-99), respectively. In 97.9% of dominant cases, an IVS3-48C allele is co-inherited with the deleterious mutation. The frequency of the IVS3-48C allele differs widely in the Japanese (43%), southeast Asian (31%), white French (11%), North African (2.7%), and black West African (<1%) populations. These differences can be related to the prevalence of EPP in these populations and could account for the absence of EPP in black subjects. The phylogenic origin of the IVS3-48C haplotypes strongly suggests that the IVS3-48C allele arose from a single recent mutational event. Estimation of the age of the IVS3-48C allele from haplotype data in white and Asian populations yields an estimated age three to four times younger in the Japanese than in the white population, and this difference may be attributable either to differing demographic histories or to positive selection for the IVS3-48C allele in the Asian population. Finally, by calculating the KA/KS ratio in humans and chimpanzees, we show that the FECH protein sequence is subject to strong negative pressure. Overall, EPP looks like a Mendelian disorder, in which the prevalence of overt disease depends mainly on the frequency of a single common single-nucleotide polymorphism resulting from a unique mutational event that occurred 60,000 years ago.

Mutations in human CPO gene predict clinical expression of either hepatic hereditary coproporphyria or erythropoietic harderoporphyria

Hereditary coproporphyria (HCP), an autosomal dominant acute hepatic porphyria, results from mutations in the gene that encodes coproporphyrinogen III oxidase (CPO). HCP (heterozygous or rarely homozygous) patients present with an acute neurovisceral crisis, sometimes associated with skin lesions. Four patients (two families) have been reported with a clinically distinct variant form of HCP. In such patients, the presence of a specific mutation (K404E) on both alleles or associated with a null allele, produces a unifying syndrome in which hematological disorders predominate: 'harderoporphyria'. Here, we report the fifth case (from a third family) with harderoporphyria. In addition, we show that harderoporphyric patients exhibit iron overload secondary to dyserythropoiesis. To investigate the molecular basis of this peculiar phenotype, we first studied the secondary structure of the human CPO by a predictive method, the hydrophobic cluster analysis (HCA) which allowed us to focus on a region of the enzyme. We then expressed mutant enzymes for each amino acid of the region of interest, as well as all missense mutations reported so far in HCP patients and evaluated the amount of harderoporphyrin in each mutant. Our results strongly suggest that only a few missense mutations, restricted to five amino acids encoded by exon 6, may accumulate significant amounts of harderoporphyrin: D400-K404. Moreover, all other type of mutations or missense mutations mapped elsewhere throughout the CPO gene, lead to coproporphyrin accumulation and subsequently typical HCP. Our findings, reinforced by recent crystallographic results of yeast CPO, shed new light on the genetic predisposition to HCP. It represents a first monogenic metabolic disorder where clinical expression of overt disease is dependent upon the location and type of mutation, resulting either in acute hepatic or in erythropoietic porphyria.

A mouse model provides evidence that genetic background modulates anemia and liver injury in erythropoietic protoporphyria

Erythropoietic protoporphyria is an inherited disorder of heme biosynthesis caused by partial ferrochelatase deficiency, resulting in protoporphyrin (PP) overproduction by erythrocytes. In humans, it is responsible for painful skin photosensitivity and, occasionally, liver failure due to accumulation of PP in the liver. The ferrochelatase deficiency mouse mutation is the best animal model available for human erythropoietic protoporphyria. The original description, based on mice with a BALB/cByJCrl genetic background, reported a disease resembling the severe form of the human disease, with anemia, jaundice, and liver failure. Using congenic strains, we investigated the effect of genetic background on the severity of the phenotype. Compared with BALB/cByJCrl, C57BL/6JCrl mice developed moderate but increasing anemia and intense liver accumulation of PP with severe hepatocyte damage and loss. Bile excretory function was not affected, and bilirubin remained low. Despite the highest PP concentration in erythrocytes, anemia was mild and there were few PP deposits in the liver in SJL/JOrlCrl homozygotes. Discriminant analysis using six hematologic and biochemical parameters showed that homozygotes of the three genetic backgrounds could be clustered in three well-separated groups. These three congenic strains provide strong evidence for independent genetic control of bone marrow contribution of PP overproduction to development of liver disease and biliary PP excretion. They provide a tool to investigate the physiological mechanisms involved in these phenotypic differences and to identify modifying genes.

Successful match-unrelated donor bone marrow transplantation for congenital erythropoietic porphyria (Günther disease)

Congenital erythropoietic porphyria (CEP; Gunther disease; OMIM 263700) is a rare autosomal recessive disorder caused by a deficiency of uroporphyrinogen III synthase (UROS). The deficiency of this enzyme is associated with lifelong overproduction of series I porphyrins which circulate and are deposited in many tissues, causing light-sensitisation and severe damage to skin beginning in childhood. Blistering and scarring of exposed areas may lead to mutilating deformities. We describe two cases: a 4-year-old boy and his first cousin who were cured of CEP by matched unrelated donor bone marrow transplants. Both are alive and disease-free 3 and 2 years post-transplant, respectively. Cutaneous lesions improved dramatically. The correction of the enzyme deficiency was confirmed by measuring erythrocyte UROS activity and urinary porphyrin excretion. Chimerism was complete for both children. Both patients were homoallelic for a novel mutation of the UROS gene, the missense mutation A69T.

CONCLUSION

Considering the severity of the disease, if HLA-matched sibling donor is not available, haematopoietic stem cell transplantation using a matched unrelated donor should be strongly considered for treating congenital erythropoietic porphyria since this is currently the only known curative therapy.

Recovery from a variegate porphyria by a liver transplantation

The porphyrias are a group of inherited or acquired enzymatic defects of heme biosynthesis. Each type of porphyria has a characteristic pattern of overproduction and accumulation of heme precursors based on the location of dysfunctional enzyme in the heme synthetic pathway. Variegate porphyria, one of the acute hepatic porphyrias, is characterized by a partial reduction in protoporphyrinogen oxidase, the seventh enzyme of the heme biosynthetic pathway. A case of liver transplantation is described with a recovery from a variegate porphyria. Acute porphyria is commonly worsened by a wide variety of medications. We describe a step-by-step perioperative management protocol.

The 3' region of the DRD2 gene is involved in genetic susceptibility to schizophrenia

The gene coding for the D2 dopamine receptor (DRD2) is considered as one of the most relevant candidate genes in schizophrenia. Previous genetic studies focusing on this gene yielded conflicting results, for example because of differences in methodology (linkage versus association studies) and variability in the loci analyzed (the DRD2 gene having many polymorphic sites). We used a progressive strategy with two different approaches (case-control and transmission disequilibrium test) and investigated six genetic polymorphisms spanning the DRD2 gene in 103 patients with DSM-IV criteria of schizophrenia, their 206 parents and 83 matched healthy control subjects. We found a significant excess of the A2 allele in subject with schizophrenia compared to unaffected controls. An excess of transmission of the A2 allele (and haplotypes containing this marker) from the parents to the affected children was also observed. Interestingly, the TaqI A1/A2 polymorphism, located 9.5 kb downstream from the DRD2 gene, maps in a novel gene, untitled "X-kinase", and leads to a 713Glu-->Lys substitution in exon 8. As the analysis of the other markers within the DRD2 gene does not improve the strength of the association, our data are in favor of a specific role of the 3' chromosomic region of the DRD2 gene in the vulnerability to schizophrenia.

Modulation of penetrance by the wild-type allele in dominantly inherited erythropoietic protoporphyria and acute hepatic porphyrias

We have recently demonstrated that in an autosomal dominant porphyria, erythropoietic protoporphyria (EPP), the coinheritance of a ferrochelatase (FECH) gene defect and of a wild-type low-expressed FECH allele is generally involved in the clinical expression of EPP. This mechanism may provide a model for phenotype modulation by minor variations in the expression of the wild-type allele in the other three autosomal dominant porphyrias that exhibit incomplete penetrance: acute intermittent porphyria (AIP), variegata porphyria (VP) and hereditary coproporphyria (HC), which are caused by partial deficiencies of hydroxy-methyl bilane synthase (HMBS), protoporphyrinogen oxidase (PPOX) and coproporphyrinogen oxidase (CPO), respectively. Given the dominant mode of inheritance of EPP, VP, AIP and HC, we first confirmed that the 200 overtly porphyric subjects (55 EPP, 58 AIP, 56 VP; 31 HC) presented a single mutation restricted to one allele (20 novel mutations and 162 known mutations). We then analysed the available single-nucleotide polymorphisms (SNPs) present at high frequencies in the general population and spreading throughout the FECH, HMBS, PPOX and the CPO genes in four case-control association studies. Finally, we explored the functional consequences of polymorphisms on the abundance of wild-type RNA, and used relative allelic mRNA determinations to find out whether low-expressed HMBS, PPOX and the CPO alleles occur in the general population. We confirm that the wild-type low-expressed allele phenomenon is usually operative in the mechanism of variable penetrance in EPP, but conclude that this is not the case in AIP and VP. For HC, the CPO mRNA determinations strongly suggest that normal CPO alleles with low-expression are present, but whether this low-expression of the wild-type allele could modulate the penetrance of a CPO gene defect in HC families remains to be ascertained.

Ancestral founder of mutation W283X in the porphobilinogen deaminase gene among acute intermittent porphyria patients

Acute intermittent porphyria (AIP) is a low-penetrant autosomal dominant disorder caused by mutations in the porphobilinogen deaminase gene (PBGD). Nearly 60% of all Swiss AIP patients carry a nonsense mutation W283X (G(7916)-->A). In France, the prevalence of W283X is <5%. To determine whether W283X was a founder mutation or originated from multiple de novo events, we studied 25 apparently unrelated W283X families and index patients, 21 of Swiss and 4 of French origins. In the absence of sufficient genealogical data to verify the ancestral background of these W283X families/patients, we identified haplotypes of seven intragenic single nucleotide polymorphisms (SNPs) in the PBGD gene as well as eight microsatellites flanking the PBGD gene covering 9.88 cM in chromosome 11. Molecular cloning and sequencing experiments were required in order to completely resolve the intragenic haplotypes in this study cohort which mainly consisted of single index patients and families with limited members. Thirteen of the 25 W283X families/patients carry a SNP haplotype [C-A-A-A-G-C-W283X-G] and 12 (including four French families) carry a [T-G-G-G-G-C-W283X-G] haplotype. A less conserved microsatellite haplotype was identified among the 25 W283X alleles which allowed us to estimate the age of the mutation. Since W283X is not explained by a methylcytosine mutation, we favor the hypothesis of a single mutational event which took place on the [T-G-G-G-G-C-G] background at approximately 40 generations or 1000 years ago. Around 550 years ago, a recombination event occurred between intron 3 and 10 of the PBGD gene which resulted in the [C-A-A-A-G-C-W283X-G] haplotype only found in a restricted region.

Combined factor V leiden (G1691A) and prothrombin (G20210A) genotyping by multiplex real-time polymerase chain reaction using fluorescent resonance energy transfer hybridization probes on the Rotor-Gene 2000

Several methods have been developed to detect common single point mutations in the factor V and prothrobin genes that are risk factors for thrombophilia. Most are based on PCR followed by restriction enzyme digestion and electrophoresis (RFLP), but gel analysis has certain limitations, and alternative detection methods, including real-time PCR, have therefore been developed. In this study we developed and evaluated a combined factor V Leiden and prothrombin (G20210A) genotyping method based on multiplex real-time PCR with fluorescent resonance energy transfer (FRET) hybridization probes on the Rotor-Gene 2000. Two hundred subjects were screened for the two mutations. The FRET assay clearly discriminated among wild-type, homozygous and heterozygous status for the two mutations, and the results were in full agreement with those of the RFLP assay. This robust FRET probe-based assay also has a higher throughput capacity than conventional methods, handling up to 72 samples in 90 min.

Male limited association of the dopamine receptor D2 gene TaqI a polymorphism and alcohol dependence

Association studies of the TaqI A allele of the dopamine receptor D2 (DRD2) gene with alcohol dependence have produced conflicting findings. Although a wide series of clinical features have been considered in the different association studies performed, very few studies specifically analyzed the role of gender. We compared the TaqI A polymorphisms of the DRD2 gene in 120 French Caucasian alcohol-dependent inpatients (62 males and 58 females) and 107 healthy ethnically matched controls (66 males and 41 females). We observed that 55% of alcohol-dependent males have at least one A1 allele, a prevalence that is significantly above that observed in the control males (38%). On the contrary, no differences were found in females between the alcohol-dependent inpatients and controls for the A1 allele prevalence. In our sample, this male-specific association was not explained by gender specificities of alcohol dependence, such as age at onset and severity measures (mean numbers of social, somatic, and withdrawal complications). On the other hand, alcohol-dependent women with the A1 allele reported more frequently a major depressive disorder (70% vs. 40%, P = 0.03). We thus replicated the allelic association of the A1 allele of the DRD2 gene with alcohol dependence, but showed a male-limited effect of this "vulnerability allele." Recent evidence for gender difference in dopamine D2-like receptor levels and affinity may explain this discrepancy.