Acute intermittent porphyria: biochemical and clinical analysis in the Argentinean population

Recent advances in the epidemiology and genetics of acute intermittent porphyria

Acute intermittent porphyria (AIP) is a dominant inherited disorder with a low penetrance that is caused by mutations in the gene coding for hydroxymethylbilane synthase (HMBS). Information about the epidemiology and molecular genetic features of this rare disorder is crucial to clinical research, and particularly to the evaluation of new treatments. Variations in the prevalence and penetrance of AIP in various studies may due to the different inclusion criteria and methods of assessment. Here, the prevalence and penetrance of AIP are analyzed systematically, and the genetic traits of different populations and findings regarding the genotype-phenotype correlation are summarized. In addition, quite a few studies have indicated that AIP susceptibility was affected by other factors, such as modifying genes. Findings regarding possible modifying genes are documented here, helping to reveal the pathogenesis of and treatments for AIP. The status of research on AIP in China reveals the lack of epidemiological and genetic studies of the Chinese population, a situation that needs to be promptly remedied.

Identification and characterization of 40 novel hydroxymethylbilane synthase mutations that cause acute intermittent porphyria

Acute intermittent porphyria (AIP), an autosomal dominant disorder due to the half-normal activity of hydroxymethylbilane synthase (HMBS), is characterized by acute neurovisceral attacks that are precipitated by factors that induce heme biosynthesis. Molecular diagnosis is the most sensitive and specific diagnostic test for AIP, and importantly, it permits the identification of asymptomatic family members for genetic counseling and avoidance of precipitating factors. Here, we report the identification of 40 novel HMBS mutations, including 11 missense, four nonsense, 16 small insertions or deletions, eight consensus splice site mutations, and a complex insertion-deletion mutation in unrelated individuals with AIP. Prokaryotic expression of the missense mutations demonstrated that all mutants had ≤5% of expressed wildtype activity, except for c.1039G>C (p.A347P), which had 51% residual HMBS activity but was markedly thermolabile. Of note, the mutation c.612G>T (p.Q204H) altered the last nucleotide of exon 10, which resulted in an alternative HMBS transcript with an in-frame nine base-pair deletion at the 3'-terminus of exon 10 (encoding protein Q204HΔ3). When expressed, Q204HΔ3 and an in-frame three base-pair deletion (c.639_641delTGC) had no detectable HMBS activity. Western blot analyses and mapping of the missense mutations on the human HMBS crystal structure revealed that mutations near the active site or at the dimerization interface resulted in stably expressed proteins, while most that altered surface residues resulted in unstable proteins, presumably due to improper protein folding. These studies identified novel pathogenic HMBS mutations and expanded the molecular heterogeneity of AIP.

Acute Hepatic Porphyrias in Colombia: An Analysis of 101 Patients

BACKGROUND

There is minimal information available about acute hepatic porphyrias (AHPs) in developing countries. The aim of this study was to describe the demographics, clinical features, and mortality of AHPs in Colombia.

PATIENTS AND METHODS

121 patients with presumed diagnosis of AHPs were reported in Colombia between 1944 and 2018. A pooled analysis of 53 patients with confirmed diagnosis was performed to evaluate the demographics, clinical features, and mortality of AHPs in the country. Selected variables were compared by periods (1952-2000 and 2001-2018).

RESULTS

Most attacks occurred in women (66%), with a women-to-man ratio of 39/14. 96% of the patients were diagnosed with AHPs between 15 and 40 years of age. Precipitants were identified in 71% of attacks and more than one precipitant in 41% of them. Drugs (85%) and infections (44%) were the most common precipitants. 11% of women had premenstrual attacks. Abdominal pain was the most common symptom (96%). Cortical blindness, posterior reversible encephalopathy syndrome, and rhabdomyolysis were described. 70% of attacks were confirmed by qualitative test only. 67% of attacks were treated with intravenous heme. The use of heme increased from 4 to 85% in the last two decades. Mortality decreased about twofold in relation to the increase in the use of heme. Severe motor neuropathy was associated with increased mortality. Gonadorelin analogues, heme prophylaxis, and orthotopic liver transplantation have been used to prevent recurrent attacks.

CONCLUSIONS

Diagnosis and treatment of AHPs in Colombia have improved in recent decades. However, there are still important shortcomings to address.

Clinical, Biochemical Characteristics and Hospital Outcome of Acute Intermittent Porphyria Patients: A Descriptive Study from North India

INTRODUCTION

Acute intermittent porphyria (AIP) is an inherited metabolic disease characterized by disordered heme biosynthesis. There is no recent study reported from India.

MATERIALS AND METHODS

It was a retrospective, observational study. Clinical records of patients of AIP with acute porphyric attacks admitted from April 2008 to December 2016 were analyzed.

RESULTS

Fifteen AIP patients constituted of eight females and seven males were analyzed. Mean age at presentation was 34.33 ± 15.86 years. Thirteen patients (86.67%) had acute flaccid paralysis (AFP). All of them had peripheral neuropathy. These patients concomitantly had abdominal pain, seizure, encephalopathy, autonomic hyperactivity, history of passage of dark urine, and electrolyte abnormality (hyponatremia) in various combinations. Abdominal pain was the presenting symptom in 11 (73.33%) patients. Seven (46.67%) patients had seizure episodes. Five patients (33.33%) had hyponatremia at presentation. Significantly higher percentage of them had seizure at presentation or during hospital stay (P = 0.007). These patients also had evidence of autonomic hyperactivity in the form of higher pulse rate, systolic and diastolic blood pressure at presentation. They had prolonged duration of hospital stay as well (P = 0.016). Eleven patients had partial recovery and rest four patients (26.67%) had in-hospital mortality.

CONCLUSION

Patients had severe neurological involvement manifesting mainly as AFP and seizure episodes. We recommend screening for AIP in patients presenting with features of AFP along with any combination of clinical/laboratory manifestations such as abdominal pain, seizure, encephalopathy, autonomic hyperactivity, passage of dark urine, and hyponatremia. Electrolyte abnormality in the form of hyponatremia was an important severity marker.

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.

Porphyric neuropathy

Porphyric neuropathy often poses a diagnostic dilemma; it is typically associated with the hepatic porphyrias, characterized by acute life-threatening attacks of neurovisceral symptoms that mimic a range of acute medical and psychiatric conditions. The development of acute neurovisceral attacks is responsive to environmental factors, including drugs, hormones, and diet. This chapter reviews the clinical manifestations, genetics, pathophysiology, and mechanisms of neurotoxicity of the acute hepatic porphyrias. While the etiology of the neurological manifestations in the acute porphyrias remains undefined, the main hypotheses include toxicity of porphyrin precursors and deficiency of heme synthesis. These hypotheses will be discussed with reference to novel experimental models of porphyric neuropathy.

Purple pigments: the pathophysiology of acute porphyric neuropathy

The porphyrias are inherited metabolic disorders arising from disturbance in the haem biosynthesis pathway. The neuropathy associated with acute intermittent porphyria (AIP) occurs due to mutation involving the enzyme porphobilinogen deaminase (PBGD) and is characterised by motor-predominant features. Definitive diagnosis often encompasses a combination of biochemical, enzyme analysis and genetic testing, with clinical neurophysiological findings of a predominantly motor axonal neuropathy. Symptomatic and supportive treatment are the mainstays during an acute attack. If administered early, intravenous haemin may prevent progression of neuropathy. While the pathophysiology of AIP neuropathy remains unclear, axonal dysfunction appears intrinsically linked to the effects of neural energy deficits acquired through haem deficiency coupled to the neurotoxic effects of porphyrin precursors. The present review will provide an overview of AIP neuropathy, including discussion of recent advances in understanding developed through neurophysiological approaches that have further delineated the pathophysiology of axonal degeneration.

Excess risk of adverse pregnancy outcomes in women with porphyria: a population-based cohort study

The porphyrias comprise a heterogeneous group of rare, primarily hereditary, metabolic diseases caused by a partial deficiency in one of the eight enzymes involved in the heme biosynthesis. Our aim was to assess whether acute or cutaneous porphyria has been associated with excess risks of adverse pregnancy outcomes. A population-based cohort study was designed by record linkage between the Norwegian Porphyria Register, covering 70% of all known porphyria patients in Norway, and the Medical Birth Registry of Norway, based on all births in Norway during 1967-2006. The risks of the adverse pregnancy outcomes preeclampsia, delivery by caesarean section, low birth weight, premature delivery, small for gestational age (SGA), perinatal death, and congenital malformations were compared between porphyric mothers and the rest of the population. The 200 mothers with porphyria had 398 singletons during the study period, whereas the 1,100,391 mothers without porphyria had 2,275,317 singletons. First-time mothers with active acute porphyria had an excess risk of perinatal death [adjusted odds ratio (OR) 4.9, 95% confidence interval (CI) 1.5-16.0], as did mothers with the hereditable form of porphyria cutanea tarda (PCT) (3.0, 1.2-7.7). Sporadic PCT was associated with an excess risk of SGA [adjusted relative risk (RR) 2.0, 1.2-3.4], and for first-time mothers, low birth weight (adjusted OR 3.4, 1.2-10.0) and premature delivery (3.5, 1.2-10.5) in addition. The findings suggest women with porphyria should be monitored closely during pregnancy.

An analysis of 112 acute porphyric attacks in Cape Town, South Africa: Evidence that acute intermittent porphyria and variegate porphyria differ in susceptibility and severity

Four forms of porphyria may present clinically with the acute attack, an episodic, severe, and potentially life-threatening manifestation characterized by abdominal and neurologic symptoms. We describe our experience with 112 consecutive attacks observed and treated in 25 patients with the 2 most common forms of acute porphyria in Cape Town, South Africa; 25 attacks in 10 patients with variegate porphyria and 87 attacks in 14 patients with acute intermittent porphyria. The remaining patient experienced more than 100 sequential, severe, and poorly remitting attacks, which are not included in our analysis. In our population, the relative risk of an acute attack in acute intermittent porphyria compared with that in variegate porphyria was 14.3 (confidence intervals, 6.3-32.7). Patients with variegate porphyria were significantly older (median age at first attack, 30 yr) than those with acute intermittent porphyria (median age at first attack, 23.5 yr; p < 0.0001), and demonstrated an equal sex ratio, whereas the male:female ratio in acute intermittent porphyria was 2:12 (p < 0.0001). There was a significant difference in the incidence of factors precipitating the acute attack. Drug exposure was a frequent precipitant of the acute attack in variegate porphyria, whereas hormonal factors were more important in acute intermittent porphyria (p < 0.00001). Patients with acute intermittent porphyria also showed a trend to earlier and more frequent recurrent acute attacks following the initial admission. Mean urine precursor levels, blood pressure, pulse rate, and heme arginate requirement were all significantly higher in patients with acute intermittent porphyria. No significant difference in the frequency of serious complications or in outcome could be shown. We describe our experience with treatment with heme arginate, and provide evidence that heme arginate results in a prompt and statistically significant improvement in symptoms. The incidence of serious complications and mortality in this series was low, confirming a trend to an increasingly good prognosis for patients with acute porphyria who receive expert treatment.

Epilepsy and porphyria: new perspectives

Porphyria is a group of disorders caused by alterations in the enzymatic pathway involved in haem biosynthesis. The clinical picture consists of extraneurological and neurological manifestations, seizures being an important feature. The pathogenesis of seizures is probably related to metabolic imbalance such as hyponatremia and to the intrinsic epileptogenic role of some porphyrins. Many studies report that neural damage can follow a porphyric attack, suggesting that these lesions can be epileptogenic. Several reports also pointed out that porphyria can be precipitated by some antiepileptic drugs (AEDs). More recent AEDs appeared and need assessment in relation to porphyria. An educational program including a registry of patients with porphyria, an intensive study of family history and the genetic background may be useful to obtain better epidemiological data and a clearer understanding of pathogenesis. Application of neuroimaging may detect epileptogenic foci, helping to define the specific risk of seizures for each patient.

International air travel: a risk factor for attacks in acute intermittent porphyria

Five patients are reported with acute intermittent porphyria in whom attacks were apparently precipitated by international air travel. In four subjects this was the initial presenting attack and in a fifth the cause of an acute relapse in a patient requiring regular haem arginate prophylaxis. Multifactorial precipitants implicated include, dehydration, missed meals, alcohol use, infection, chronic hypoxia, premenstrual syndrome and stress. Acute intermittent porphyria should be suspected in individuals presenting with unexplained acute abdominal pain following international air travel. Appropriate precautions may reduce the incidence of attacks in known porphyrics.

Acute intermittent porphyria in women: clinical expression, use and experience of exogenous sex hormones. A population-based study in northern Sweden

OBJECTIVE

To describe the clinical expression of acute intermittent porphyria (AIP) in women, their use of exogenous sex hormones, and the effects on AIP.

DESIGN

A retrospective population-based study.

SUBJECTS

All women aged > or =18 years (n = 190) with DNA-diagnosed AIP in northern Sweden.

RESULTS

A total of 166 women (87%) participated; 91 (55%) had manifest AIP. Severe attacks were reported by 82%; 39% reported recurrent premenstrual AIP attacks and 22% reported chronic AIP symptoms. Oral hormonal contraceptives had been used by 58% of all these women and by 50 with manifest AIP (57%). Twelve women (24%) associated oral contraceptives as precipitating AIP attacks; in nine cases their first attack. One woman experienced relief from AIP symptoms. On commencing their treatment, 72% of the women with manifest AIP had not yet suffered their first attack. Twenty-two women (25%) aged > or =45 years had used hormonal replacement therapy (HRT) at menopause to remedy climacteric symptoms (the percutaneous route was most frequently used); no AIP attack was precipitated. HRT to remedy vaginal dryness was used by 26 women (28%) aged > or =45 years without triggering an AIP attack. Miscarriages were more frequent in women with manifest AIP (50%) than in the latent group (30%, P = 0.014).

CONCLUSIONS

About half of the women with AIP had used oral hormonal contraceptives. As 25% of women with manifest AIP reported attacks associated with such drugs, caution must still be recommended. Menopausal HRT only rarely affected the disorder. Miscarriage was more common amongst women with manifest AIP.

Delta-aminolevulinic acid cytotoxic effects on human hepatocarcinoma cell lines

BACKGROUND

Acute Intermittent Porphyria is a genetic disorder of heme metabolism, characterized by increased levels of porphyrin precursors, delta-aminolevulinic acid (ALA) and porphobilinogen (PBG). ALA has been reported to generate reactive oxygen species and to cause oxidative damage to proteins, subcellular structures and DNA. It is known that oxidative stress can induce apoptosis. The aim of this work was to study the cytotoxic effect of ALA on two hepatocarcinoma cell lines.

RESULTS

We have determined the impact of ALA on HEP G2 and HEP 3B hepatocarcinoma cell lines survival as measured by the MTT assay. ALA proved to be cytotoxic in both cell lines however; HEP G2 was more sensitive to ALA than HEP 3B. Addition of hemin or glucose diminished ALA cytotoxicity in HEP G2 cells; instead it was enhanced in HEP 3B cells. Because apoptosis is usually associated with DNA fragmentation, the DNA of ALA treated and untreated cells were analyzed. The characteristic pattern of DNA fragmentation ladders was observed in ALA treated cells. To elucidate the mechanisms of ALA induced apoptosis, we examined its effect on p53 expression. No changes in p53 mRNA levels were observed after exposure of both cell lines to ALA for 24 h. CDK2 and CDK4 protein levels were reduced after ALA treatment at physiological concentrations.