Emerging therapies for acute intermittent porphyria

Exploring current and emerging therapies for porphyrias

Porphyrias are rare, mostly inherited disorders resulting from altered activity of specific enzymes in the haem synthesis pathway that lead to accumulation of pathway intermediates. Photocutaneous symptoms occur when excess amounts of photoreactive porphyrins circulate in the blood to the skin, whereas increases in potentially neurotoxic porphyrin precursors are associated with neurovisceral symptoms. Current therapies are suboptimal and their mechanisms are not well established. As described here, emerging therapies address underlying disease mechanisms by introducing a gene, RNA or other specific molecule with the potential to cure or slow progression of the disease. Recent progress in nanotechnology and nanoscience, particularly regarding particle design and formulation, is expanding disease targets. More secure and efficient drug delivery systems have extended our toolbox for transferring specific molecules, especially into hepatocytes, and led to proof-of-concept studies in animal models. Repurposing existing drugs as molecular chaperones or haem synthesis inhibitors is also promising. This review summarizes key examples of these emerging therapeutic approaches and their application for hepatic and erythropoietic porphyrias.

When rare meets common: Treatable genetic diseases are enriched in the general psychiatric population

Mental illnesses are one of the biggest contributors to the global disease burden. Despite the increased recognition, diagnosis and ongoing research of mental health disorders, the etiology and underlying molecular mechanisms of these disorders are yet to be fully elucidated. Moreover, despite many treatment options available, a large subset of the psychiatric patient population is nonresponsive to standard medications and therapies. There has not been a comprehensive study to date examining the burden and impact of treatable genetic disorders (TGDs) that can present with neuropsychiatric features in psychiatric patient populations. In this study, we test the hypothesis that TGDs that present with psychiatric symptoms are more prevalent within psychiatric patient populations compared to the general population by performing targeted next-generation sequencing of 129 genes associated with 108 TGDs in a cohort of 2301 psychiatric patients. In total, 48 putative affected and 180 putative carriers for TGDs were identified, with known or likely pathogenic variants in 79 genes. Despite screening for only 108 genetic disorders, this study showed a two-fold (2.09%) enrichment for genetic disorders within the psychiatric population relative to the estimated 1% cumulative prevalence of all single gene disorders globally. This strongly suggests that the prevalence of these, and most likely all, genetic diseases is greatly underestimated in psychiatric populations. Increasing awareness and ensuring accurate diagnosis of TGDs will open new avenues to targeted treatment for a subset of psychiatric patients.

Acute Intermittent Porphyria’s Symptoms and Management: A Narrative Review

Acute intermittent porphyria (AIP) is an autosomal dominant disorder of heme biosynthesis in the liver that is caused by the accumulation of toxic heme metabolites aminolevulinic acid (ALA) and porphobilinogen (PBG) due to a deficiency in the enzyme hydroxymethylbilane synthase (HMBS). The prevalence of AIP is found to commonly affect females of reproductive age (ages 15-50) and people of Northern European descent. The clinical manifestations of AIP include acute and chronic symptoms that can be outlined into three phases: the prodromal phase, the visceral symptom phase, and the neurological phase. Major clinical symptoms involve severe abdominal pain, peripheral neuropathy, autonomic neuropathies, and psychiatric manifestations. Symptoms are often heterogeneous and vague, which can lead to life-threatening signs if not treated and managed appropriately. Whether treating AIP in its acute or chronic form, the cornerstone of treatment consists of the suppression of the production of ALA and PBG. The mainstay of managing acute attacks continues to comprise discontinuing porphyrogenic agents, adequate caloric support, heme treatment, and the treatment of symptoms. In recurrent attacks and chronic management, prevention is key with the consideration of liver transplantation and/or renal transplantation. In recent years, there has been great interest in emerging treatments that focus on a molecular level such as enzyme replacement therapy, ALAS1 gene inhibition, and even liver gene therapy (GT), which has changed the way of traditionally managing this disease and will pave the way for innovative therapies to come.

Cutting-Edge Therapies and Novel Strategies for Acute Intermittent Porphyria: Step-by-Step towards the Solution

Acute intermittent porphyria (AIP) is an autosomal dominant disease caused by the hepatic deficiency of porphobilinogen deaminase (PBGD) and the slowdown of heme biosynthesis. AIP symptomatology includes life-threatening, acute neurovisceral or neuropsychiatric attacks manifesting in response to precipitating factors. The latter promote the upregulation of 5-aminolevulinic acid synthase-1 (ALAS1), the first enzyme of heme biosynthesis, which promotes the overload of neurotoxic porphyrin precursors. Hemin or glucose infusions are the first-line therapies for the reduction of ALAS1 levels in patients with mild to severe AIP, while liver transplantation is the only curative treatment for refractory patients. Recently, the RNA-interference against ALAS1 was approved as a treatment for adult and adolescent patients with AIP. These emerging therapies aim to substitute dysfunctional PBGD with adeno-associated vectors for genome editing, human PBGD mRNA encapsulated in lipid nanoparticles, or PBGD protein linked to apolipoprotein A1. Finally, the impairment of glucose metabolism linked to insulin resistance, and mitochondrial aberrations during AIP pathophysiology provided new therapeutic targets. Therefore, the use of liver-targeted insulin and insulin-mimetics such as α-lipoic acid may be useful for overcoming metabolic dysfunction in these subjects. Herein, the present review aims to provide an overview of AIP pathophysiology and management, focusing on conventional and recent therapeutical approaches.

Enzyme Therapy: Current Challenges and Future Perspectives

In recent years, enzymes have risen as promising therapeutic tools for different pathologies, from metabolic deficiencies, such as fibrosis conditions, ocular pathologies or joint problems, to cancer or cardiovascular diseases. Treatments based on the catalytic activity of enzymes are able to convert a wide range of target molecules to restore the correct physiological metabolism. These treatments present several advantages compared to established therapeutic approaches thanks to their affinity and specificity properties. However, enzymes present some challenges, such as short in vivo half-life, lack of targeted action and, in particular, patient immune system reaction against the enzyme. For this reason, it is important to monitor serum immune response during treatment. This can be achieved by conventional techniques (ELISA) but also by new promising tools such as microarrays. These assays have gained popularity due to their high-throughput analysis capacity, their simplicity, and their potential to monitor the immune response of patients during enzyme therapies. In this growing field, research is still ongoing to solve current health problems such as COVID-19. Currently, promising therapeutic alternatives using the angiotensin-converting enzyme 2 (ACE2) are being studied to treat COVID-19.

Acute Intermittent Porphyria: An Overview of Therapy Developments and Future Perspectives Focusing on Stabilisation of HMBS and Proteostasis Regulators

Acute intermittent porphyria (AIP) is an autosomal dominant inherited disease with low clinical penetrance, caused by mutations in the hydroxymethylbilane synthase (HMBS) gene, which encodes the third enzyme in the haem biosynthesis pathway. In susceptible HMBS mutation carriers, triggering factors such as hormonal changes and commonly used drugs induce an overproduction and accumulation of toxic haem precursors in the liver. Clinically, this presents as acute attacks characterised by severe abdominal pain and a wide array of neurological and psychiatric symptoms, and, in the long-term setting, the development of primary liver cancer, hypertension and kidney failure. Treatment options are few, and therapies preventing the development of symptomatic disease and long-term complications are non-existent. Here, we provide an overview of the disorder and treatments already in use in clinical practice, in addition to other therapies under development or in the pipeline. We also introduce the pathomechanistic effects of HMBS mutations, and present and discuss emerging therapeutic options based on HMBS stabilisation and the regulation of proteostasis. These are novel mechanistic therapeutic approaches with the potential of prophylactic correction of the disease by totally or partially recovering the enzyme functionality. The present scenario appears promising for upcoming patient-tailored interventions in AIP.

The genetic landscape of axonal neuropathies in the middle-aged and elderly: Focus on MME

OBJECTIVE

To test the hypothesis that monogenic neuropathies such as Charcot-Marie-Tooth disease (CMT) contribute to frequent but often unexplained neuropathies in the elderly, we performed genetic analysis of 230 patients with unexplained axonal neuropathies and disease onset ≥35 years.

METHODS

We recruited patients, collected clinical data, and conducted whole-exome sequencing (WES; n = 126) and MME single-gene sequencing (n = 104). We further queried WES repositories for MME variants and measured blood levels of the MME-encoded protein neprilysin.

RESULTS

In the WES cohort, the overall detection rate for assumed disease-causing variants in genes for CMT or other conditions associated with neuropathies was 18.3% (familial cases 26.4%, apparently sporadic cases 12.3%). MME was most frequently involved and accounted for 34.8% of genetically solved cases. The relevance of MME for late-onset neuropathies was further supported by detection of a comparable proportion of cases in an independent patient sample, preponderance of MME variants among patients compared to population frequencies, retrieval of additional late-onset neuropathy patients with MME variants from WES repositories, and low neprilysin levels in patients' blood samples. Transmission of MME variants was often consistent with an incompletely penetrant autosomal-dominant trait and less frequently with autosomal-recessive inheritance.

CONCLUSIONS

A detectable fraction of unexplained late-onset axonal neuropathies is genetically determined, by variants in either CMT genes or genes involved in other conditions that affect the peripheral nerves and can mimic a CMT phenotype. MME variants can act as completely penetrant recessive alleles but also confer dominantly inherited susceptibility to axonal neuropathies in an aging population.

Therapeutic strategies for acute intermittent porphyria

Acute intermittent porphyria (AIP) is an autosomal dominant disease caused by mutations in porphobilinogen deaminase (PBGD), the third enzyme of the heme synthesis pathway. Symptoms of AIP usually manifest as intermittent acute attacks with occasional neuropsychiatric crises. The management of AIP includes treatment of acute attacks, prevention of attacks, long-term monitoring and treatment of chronic complications. Intravenous injection of heme is the most effective method of treating acute attacks. Carbohydrate loading is used when heme is unavailable or in the event of mild attacks. Symptomatic treatment is also needed during attacks. Prevention of attacks includes eliminating precipitating factors, heme prophylaxis and liver transplantation. New treatment options include givosiran (siRNA) to down-regulate ALA synthase-1 (ALAS1) and the messenger RNA of PBGD (PBGD mRNA) delivered to the liver cells of patients with AIP. Long-term monitoring of chronic complications includes regular liver-kidney function and hepatocellular carcinoma (HCC) screening.

Combined liver-kidney transplantation for rare diseases

Combined liver and kidney transplantation (CLKT) is indicated in patients with failure of both organs, or for the treatment of end-stage chronic kidney disease (ESKD) caused by a genetic defect in the liver. The aim of the present review is to provide the most up-to-date overview of the rare conditions as indications for CLKT. They are major indications for CLKT in children. However, in some of them (e.g., atypical hemolytic uremic syndrome or primary hyperoxaluria), CLKT may be required in adults as well. Primary hyperoxaluria is divided into three types, of which type 1 and 2 lead to ESKD. CLKT has been proven effective in renal function replacement, at the same time preventing recurrence of the disease. Nephronophthisis is associated with liver fibrosis in 5% of cases and these patients are candidates for CLKT. In alpha 1-antitrypsin deficiency, hereditary C3 deficiency, lecithin cholesterol acyltransferase deficiency and glycogen storage diseases, glomerular or tubulointerstitial disease can lead to chronic kidney disease. Liver transplantation as a part of CLKT corrects underlying genetic and consequent metabolic abnormality. In atypical hemolytic uremic syndrome caused by mutations in the genes for factor H, successful CLKT has been reported in a small number of patients. However, for this indication, CLKT has been largely replaced by eculizumab, an anti-C5 antibody. CLKT has been well established to provide immune protection of the transplanted kidney against donor-specific antibodies against class I HLA, facilitating transplantation in a highly sensitized recipient.

High-Capacity Adenoviral Vectors: Expanding the Scope of Gene Therapy

The adaptation of adenoviruses as gene delivery tools has resulted in the development of high-capacity adenoviral vectors (HC-AdVs), also known, helper-dependent or “gutless”. Compared with earlier generations (E1/E3-deleted vectors), HC-AdVs retain relevant features such as genetic stability, remarkable efficacy of in vivo transduction, and production at high titers. More importantly, the lack of viral coding sequences in the genomes of HC-AdVs extends the cloning capacity up to 37 Kb, and allows long-term episomal persistence of transgenes in non-dividing cells. These properties open a wide repertoire of therapeutic opportunities in the fields of gene supplementation and gene correction, which have been explored at the preclinical level over the past two decades. During this time, production methods have been optimized to obtain the yield, purity, and reliability required for clinical implementation. Better understanding of inflammatory responses and the implementation of methods to control them have increased the safety of these vectors. We will review the most significant achievements that are turning an interesting research tool into a sound vector platform, which could contribute to overcome current limitations in the gene therapy field.

Disease pharmacokinetic-pharmacodynamic modelling in acute intermittent porphyria to support the development of mRNA-based therapies

BACKGROUND AND PURPOSE

Acute intermittent porphyria (AIP) results from haplo-insufficiency of the porphobilinogen deaminase (PBGD) gene encoding the third enzyme in the haem biosynthesis pathway. As liver is the main organ of pathology for AIP, emerging therapies that restore enzyme hepatic levels are appealing. The objective of this work was to develop a mechanistic-based computational framework to describe the effects of novel PBGD mRNA therapy on the accumulation of neurotoxic haem precursors in small and large animal models.

EXPERIMENTAL APPROACH

Liver PBGD activity data and/or 24-hr urinary haem precursors were obtained from genetic AIP mice and wild-type mice, rats, rabbits, and macaques. To mimic acute attacks, porphyrogenic drugs were administered over one or multiple challenges, and animals were used as controls or treated with different PBGD mRNA products. Available experimental data were sequentially used to build and validate a semi-mechanistic mathematical model using non-linear mixed-effects approach.

KEY RESULTS

The developed framework accounts for the different biological processes involved (i.e., mRNA sequence, release from lipid nanoparticle and degradation, mRNA translation, increased PBGD activity in liver, and haem precursor metabolism) in a simplified mechanistic fashion. The model, validated using external data, shows robustness in the extrapolation of PBGD activity data in rat, rabbit, and non-human primate species.

CONCLUSION AND IMPLICATIONS

This quantitative framework provides a valuable tool to compare PBGD mRNA drug products during early preclinical stages, optimize the amount of experimental data required, and project results to humans, thus supporting drug development and clinical dose and dosing regimen selection.

Acute intermittent porphyria: A case report

El término 'porfiria' proviene del griego 'porphyra' y alude a un grupo heterogéneo de trastornos metabólicos causados por una deficiencia enzimática en la biosíntesis del grupo hemo. La causa de la porfiria intermitente aguda es la deficiencia de la enzima deaminasa del porfobilinógeno.

Se presenta el caso de una mujer de 40 años que presentó dolor abdominal de 10 días de evolución, trastorno hidroelectrolítico grave debido a hiponatremia e hipopotasemia, taquicardia e hipertensión arterial sistémica persistentes, por lo cual fue sometida a una laparotomía en la que no se encontró ninguna afección de origen quirúrgico, A los siete días del examen inicial, la paciente desarrolló cuadriparesia flácida aguda y presentó una crisis convulsiva tónico-clónica generalizada. Los estudios neurofisiológicos evidenciaron una polineuropatía axonal mixta, y los valores de porfobilinógeno y porfirinas en orina eran elevados. Tras diagnosticarse porfiria intermitente aguda, esta se trató con hemina, lo que estabilizó los signos clínicos y normalizó el porfobilinógeno. La prevalencia de esta enfermedad es de 1 en 2.000 personas. Tiene un patrón de herencia autosómico dominante y se manifiesta principalmente en mujeres con edades entre los 20 y los 40 años. La enfermedad cursa con síntomas neurológicos y viscerales, y se trata con la administración de hemina y dextrosa, evitando las soluciones hipotónicas por el riesgo de exacerbar la hiponatremia.

Acute hepatic porphyrias: Current diagnosis & management

Each of the four acute hepatic porphyrias is due to mutation of an enzyme in the heme biosynthetic pathway. The accumulation of pathway intermediates that occur most notably when these diseases are active is the basis for screening and establishing a biochemical diagnosis of these rare disorders. Measurement of enzyme activities and especially DNA testing also are important for diagnosis. Suspicion of the diagnosis and specific testing, particularly measurement of urinary porphobilinogen, are often delayed because the symptoms are nonspecific, even when severe. Urinary porphyrins are also measured, but their elevation is much less specific. If porphobilinogen is elevated, second line testing will establish the type of acute porphyria. DNA testing identifies the familial mutation and enables screening of family members. Management includes removal of triggering factors whenever possible. Intravenous hemin is the most effective treatment for acute attacks. Carbohydrate loading is sometimes used for mild attacks. Cyclic attacks, if frequent, can be prevented by a GnRH analogue. Frequent noncyclic attacks are sometime preventable by scheduled (e.g. weekly) hemin infusions. Long term complications may include chronic pain, renal impairment and liver cancer. Other treatments, including RNA interference, are under development.

Computational disease model of phenobarbital-induced acute attacks in an acute intermittent porphyria mouse model

INTRODUCTION

Acute intermittent porphyria (AIP) is characterized by hepatic over-production of the heme precursors when aminolevulinic acid (ALA)-synthase 1 is induced by endogenous or environmental factors. The aim of this study was to develop a semi-mechanistic computational model to characterize urine accumulation of heme precursors during acute attacks based on experimental pharmacodynamics data and support the development of new therapeutic strategies.

METHODS

Male AIP mice received recurrent phenobarbital challenge starting on days 1, 9, 16 and 30. 24-h urine excretion of ALA, porphobilinogen (PBG) and porphyrins from challenges D1, D9 and D30 constituted the training data set to build the mechanistic model using the population approach. In a second study, porphyrin and porphyrin precursor excretion from challenge D16 were used as a validation data set.

RESULTS

The computational model presented the following features: (i) urinary excretion of ALA, PBG and porphyrins was governed by unmeasured circulating heme precursor amounts, (ii) the circulating amounts of ALA and PBG were the precursors of circulating amounts of PBG and porphyrins, respectively, and (iii) the phenobarbital effect linearly increased the synthesis of circulating ALA and PBG levels. The model displayed good parameter precision (coefficient of variation below 32% in all parameters), and adequately described the experimental data. Finally, a theoretical hemin effect was implemented to illustrate the applicability of the model to dosage optimization in drug therapies.

CONCLUSIONS

A semi-mechanistic disease model was successfully developed to describe the temporal evolution of urinary heme precursor excretion during recurrent biochemical-induced acute attacks in AIP mice. This model represents the first computational approach to explore and optimize current and new therapies.

Acute intermittent porphyria: analgesia can be dangerous

Acute intermittent porphyria (AIP) is a rare condition, a metabolic disorder of the haem biosynthesis. An acute crisis of AIP can present as a combination of symptoms, such as abdominal pain, autonomic dysfunction, hyponatremia, muscle weakness and neurological symptoms in the absence of others obvious causes. We report the case of a 53-year-old woman, who was previously diagnosed with AIP 5 weeks after therapeutic suspension has developed an acute disease exacerbation. During hospitalisation, further exacerbation has occurred after analgesia with metamizole. Glucose and hemin infusions resulted in slow improvement. Physical rehabilitation was crucial to peripheral polyneuropathy recovery. Taking into account the porphyrinogenic effect described for metamizole, this drug might have triggered the second attack. Clinical history was sufficient to suspect the diagnosis and to start the treatment immediately, preventing important sequelae.

Current and innovative emerging therapies for porphyrias with hepatic involvement

Porphyrias are rare inherited disorders caused by specific enzyme dysfunctions in the haem synthesis pathway, which result in abnormal accumulation of specific pathway intermediates. The symptoms depend upon the chemical characteristics of these substances. Porphyrins are photoreactive and cause photocutaneous lesions on sunlight-exposed areas, whereas accumulation of porphyrin precursors is related to acute neurovisceral attacks. Current therapies are suboptimal and mostly address symptoms rather than underlying disease mechanisms. Advances in the understanding of the molecular bases and pathogenesis of porphyrias have paved the way for the development of new therapeutic strategies. In this Clinical Trial Watch we summarise the basic principles of these emerging approaches and what is currently known about their application to porphyrias of hepatic origin or with hepatic involvement.

Clinical Guide and Update on Porphyrias

Physicians should be aware of porphyrias, which could be responsible for unexplained gastrointestinal, neurologic, or skin disorders. Despite their relative rarity and complexity, most porphyrias can be easily defined and diagnosed. They are caused by well-characterized enzyme defects in the complex heme biosynthetic pathway and are divided into categories of acute vs non-acute or hepatic vs erythropoietic porphyrias. Acute hepatic porphyrias (acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and aminolevulinic acid dehydratase deficient porphyria) manifest in attacks and are characterized by overproduction of porphyrin precursors, producing often serious abdominal, psychiatric, neurologic, or cardiovascular symptoms. Patients with variegate porphyria and hereditary coproporphyria can present with skin photosensitivity. Diagnosis relies on measurement of increased urinary 5-aminolevulinic acid (in patients with aminolevulinic acid dehydratase deficient porphyria) or increased 5-aminolevulinic acid and porphobilinogen (in patients with other acute porphyrias). Management of attacks requires intensive care, strict avoidance of porphyrinogenic drugs and other precipitating factors, caloric support, and often heme therapy. The non-acute porphyrias are porphyria cutanea tarda, erythropoietic protoporphyria, X-linked protoporphyria, and the rare congenital erythropoietic porphyria. They lead to the accumulation of porphyrins that cause skin photosensitivity and occasionally severe liver damage. Secondary elevated urinary or blood porphyrins can occur in patients without porphyria, for example, in liver diseases, or iron deficiency. Increases in porphyrin precursors and porphyrins are also found in patients with lead intoxication. Patients with porphyria cutanea tarda benefit from iron depletion, hydroxychloroquine therapy, and, if applicable, elimination of the hepatitis C virus. An α-melanocyte-stimulating hormone analogue can reduce sunlight sensitivity in patients with erythropoietic protoporphyria or X-linked protoporphyria. Strategies to address dysregulated or dysfunctional steps within the heme biosynthetic pathway are in development.

Messenger RNA therapy for rare genetic metabolic diseases

Decades of intense research in molecular biology and biochemistry are fructifying in the emergence of therapeutic messenger RNAs (mRNA) as a new class of drugs. Synthetic mRNAs can be sequence optimised to improve translatability into proteins, as well as chemically modified to reduce immunogenicity and increase chemical stability using naturally occurring uridine modifications. These structural improvements, together with the development of safe and efficient vehicles that preserve mRNA integrity in circulation and allow targeted intracellular delivery, have paved the way for mRNA-based therapeutics. Indeed, mRNAs formulated into biodegradable lipid nanoparticles are currently being tested in preclinical and clinical studies for multiple diseases including cancer immunotherapy and vaccination for infectious diseases. An emerging application of mRNAs is the supplementation of proteins that are not expressed or are not functional in a regulated and tissue-specific manner. This so-called 'protein replacement therapy' could represent a solution for genetic metabolic diseases currently lacking effective treatments. Here we summarise this new class of drugs and discuss the preclinical evidence supporting the potential of liver-mediated mRNA therapy for three rare genetic conditions: methylmalonic acidaemia, acute intermittent porphyria and ornithine transcarbamylase deficiency.

Molecular genetic study of acute intermittent porphyria in Russia: HMBS gene mutation spectrum and problem of penetrance

Acute intermittent porphyria (AIP) is the most common and severe form of porphyrias. This is a dominant inherited disorder with low penetrance, caused by mutations in gene coding hydroxymethylbilane synthase (HMBS). We present the results of our long-term genetic study of AIP patients and their relatives (N = 153 and 302, respectively). We detected 88 HMBS gene mutations, 24 of which never described before. To identify additional factors conditioning AIP manifestation, we carried out whole exome sequencing on the group of AIP patients (N = 6). Mutation spectra of different patients virtually did not overlap. In 5 out of 6 patients, we found defects in genes regulating nervous system (UNC13A, ALG8, FBXO38, AGRN, DOK7, SCN4A). As usually acute AIP attacks have various neurological symptoms, we proposed a hypothesis of possible contribution of mutations in such genes in AIP manifestation.

Bioengineered PBGD variant improves the therapeutic index of gene therapy vectors for acute intermittent porphyria

A first-in-human gene therapy trial using a recombinant adeno-associated viral (rAAV) vector for acute intermittent porphyria (AIP) reveals that higher doses would be required to reach therapeutic levels of the porphobilinogen deaminase (PBGD) transgene. We developed a hyperfunctional PBGD protein to improve the therapeutic index without increasing vector dose. A consensus protein sequence from 12 mammal species was compared to the human PBGD sequence, and eight amino acids were selected. I291M and N340S variants showed the highest increase in enzymatic activity when expressed in prokaryotic and eukaryotic systems. In silico analysis indicates that isoleucine 291 to methionine and asparagine 340 to serine variants did not affect the active site of the enzyme. In vitro analysis indicated a synergistic interaction between these two substitutions that improve kinetic stability. Finally, full protection against a phenobarbital-induced attack was achieved in AIP mice after the administration of 1 × 1011 gc/kg of rAAV2/8-PBGD-I291M/N340S vector; three times lower than the dose required to achieve full protection with the control rAAV2/8-hPBGD vector. In conclusion, we have developed and characterized a hyperfunctional PBGD protein. The inclusion of this variant sequence in a rAAV2/8 vector allows the effective dose to be lowered in AIP mice.

Medical and financial burden of acute intermittent porphyria

INTRODUCTION

A small proportion of patients with acute intermittent porphyria (AIP) suffer from recurrent porphyric attacks, with a severely diminished quality of life. In this retrospective case-control study, the burden of disease is quantified and compared among three AIP patient subgroups: cases with recurrent attacks, cases with one or occasional attacks and asymptomatic carriers.

METHODS

Data from patient records and questionnaires were collected in patients between 1960 and 2016 at the Erasmus Medical Center, Rotterdam, the Netherlands. We collected symptoms related to porphyria, porphyria related complications, attack frequency, hospitalisation frequency, hospitalisation days related to acute porphyric attacks, frequency of heme infusions and medical healthcare costs based on hospitalisations and heme therapy.

RESULTS

In total 11 recurrent AIP cases, 24 symptomatic AIP cases and 53 AIP carriers as controls were included. All recurrent patients reported porphyria related symptoms, such as pain, neurological and/or psychiatric disorders, and nearly all developed complications, such as hypertension and chronic kidney disease. In the recurrent cases group, the median lifelong number of hospitalisation days related to porphyric attacks was 82 days per patient (range 10-374), and they spent a median of 346 days (range 34-945) at a day-care facility for prophylactic heme therapy; total follow-up time was 243 person-years (PYRS). In the symptomatic non-recurrent group the median lifelong number of hospitalisation days related to porphyric attacks was 7 days per patient (range 1-78), total follow-up time was 528 PYRS. The calculated total medical healthcare cost for recurrent cases group was €5.8 million versus €0.3 million for the symptomatic cases group.

Effect of Menstrual Cycle on Acute Intermittent Porphyria

A 16-year-old female who was attended as an outpatient reported localized, acute abdominal pain with vomiting, symmetrical motor weakness, and burning sensation in both arms and legs. Her medical history showed irrational behavior, repeated admissions at the emergency units of many other reference hospitals, where she had been investigated for celiac disease and treated with analgesics for pain events. Her clinical condition remained unchanged despite the use of many oral analgesics. In those admissions, she showed dysautonomia, vomiting, and abdominal pain. Diagnosis investigation disclosed a notable serum hyponatremia (133.7 mEq/L). She was referred for endoscopy and the histopathological lesion of the antrum in the stomach did not show neoplastic lesions. Colonoscopy, pelvic magnetic resonance imaging (MRI), total abdominal computed tomography, and video laparoscopy were without significant abnormalities. Suspicion of acute intermittent porphyria was confirmed by quantitative urine porphobilinogen-level tests and genetic analysis. Patient was successfully treated with intravenous infusion of glucose and hemin therapy.