from the American Gastroenterological Association.
For acute attacks, treatment should include intravenous hemin, and for patients with recurrent attacks, a newly-approved therapy called givosiran should be considered, wrote the authors of the update, which was published Jan. 13 in Gastroenterology.
Dr. Brian Wang
“Diagnoses of AHPs are often missed, with a delay of more than 15 years from initial presentation. The key to early diagnosis is to consider the diagnosis, especially in patients with recurring severe abdominal pain not ascribable to other causes,” wrote the authors, who were led by Bruce Wang, MD, a hepatologist with the University of California, San Francisco.
AHPs are inherited disorders of heme-metabolism, which include acute intermittent porphyria, hereditary coproporphyria, variegate porphyria, and porphyria due to severe deficiency of 5-aminolevulinic acid dehydratase.
Acute intermittent porphyria (AIP) is the most common type, with an estimated prevalence of symptomatic AHP of 1 in 100,000 patients. However, population-level genetic studies show that the prevalence of pathogenic variants for AIP is between 1 in 1,300 and 1 in 1,785.
The major clinical presentation includes attacks of severe abdominal pain, nausea, vomiting, constipation, muscle weakness, neuropathy, tachycardia, and hypertension, yet without peritoneal signs or abnormalities on cross-sectional imaging.
Recent advances in treatment have improved the outlook for patients with AHP. To provide timely guidance, the authors developed 12 clinical practice advice statements on the diagnosis and management of AHPs based on a review of the published literature and expert opinion.
First, AHP screening should be considered in the evaluation of all patients, particularly among women in their childbearing years between ages 15 and 50 with unexplained, recurrent severe abdominal pain that doesn’t have a clear etiology. About 90% of patients with symptomatic AHP are women, and more than 90% of them experience only one or a few acute attacks in their lifetime, which are often precipitated by factors that increase the activity of the enzyme ALAS1 in the liver.
For initial AHP diagnosis, biochemical testing should measure porphobilinogen (PBG) and delta-aminolevulinic acid (ALA) corrected to creatine on a random urine sample. All patients with significantly elevated urinary PBG or ALA should initially be presumed to have AHP, and during acute attacks, both will be elevated at least five-fold of the upper limit of normal. Because ALA and PBG are porphyrin precursors, urine porphyrin testing should not be used alone for AHP screening.
After that, genetic testing should be used to confirm the AHP diagnosis, as well as the specific type of AHP. Sequencing of the four genes ALAD, HMBS, CPOX, and PPOX leads to aminolevulinic acid dehydrase deficiency, acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria, respectively. When whole-gene sequencing is performed, about 95%-99% of cases can be identified. First-degree family members should be screened with genetic testing, and those who are mutation carriers should be counseled.
For acute attacks of AHP that are severe enough to require hospitalization, the currently approved treatment is intravenous hemin infusion, usually given once daily at a dose of 3-4 mg/kg body weight for 3-5 days. Due to potential thrombophlebitis, it’s best to administer hemin in a high-flow central vein via a peripherally inserted central catheter or central port.
In addition, treatment for acute attacks should include analgesics, antiemetics, and management of systemic arterial hypertension, tachycardia, hyponatremia, and hypomagnesemia. The primary goal of treatment during an acute attack is to decrease ALA production. Patients should be counseled to avoid identifiable triggers, such as porphyrinogenic medications, excess alcohol intake, tobacco use, and caloric deprivation.
Although recent advances have improved treatment for acute attacks, management for patients with frequent attacks remains challenging, the study authors wrote. About 3%-5% of patients with symptomatic AHP experience recurrent attacks, which is defined as four or more attacks per year. These attacks aren’t typically associated with identifiable triggers, although some that occur during the luteal phase of a patient’s menstrual cycle are believed to be triggered by progesterone. However, treatment with hormonal suppression therapy, such as GnRH agonists, has had limited success.
Off-label use of prophylactic intravenous heme therapy is common, although the effectiveness in preventing recurrent attacks isn’t well-established. In addition, chronic hemin use is associated with several complications, including infections, iron overload, and the need for indwelling central venous catheters.
Recently, the Food and Drug Administration approved givosiran, a small interfering RNA-based therapy that targets delta-aminolevulinate synthase 1, for treatment in adults with AHP. Monthly subcutaneous therapy appears to significantly lower rates of acute attacks among patients who experience recurrent attacks.
“We suggest prescribing givosiran only for those patients with recurrent acute attacks that are both biochemically and genetically confirmed,” the authors wrote. “Due to limited safety data, givosiran should not be used in women who are pregnant or planning a pregnancy.”
In the most severe cases, liver transplantation should be limited to patients with intractable symptoms and a significantly decreased quality of life who are refractory to pharmacotherapy. If living donor transplantation is considered, genetic testing should be used to screen related living donors since HMBS pathogenic variants in asymptomatic donors could results in poor posttransplantation outcomes.
In the long-term, patients with AHP should be monitored annually for liver disease and chronic kidney disease with serum creatinine and estimated glomerular filtration rate monitored. Patients also face an increased risk of hepatocellular carcinoma and should start screening at age 50, with a liver ultrasound every 6 months.
“Fortunately, most people with genetic defects never experience severe acute attacks or may experience only one or a few attacks throughout their lives,” the authors wrote.
The authors (Bruce Wang, MD, Herbert L. Bonkovsky, MD, AGAF, and Manisha Balwani, MD, MS) reported that they are part of the Porphyrias Consortium. The Porphyrias Consortium is part of the Rare Diseases Clinical Research Network, an initiative of the Division of Rare Diseases Research Innovation at the National Center for Advancing Translational Sciences. The consortium is funded through a collaboration between the center and the National Institute of Diabetes and Digestive and Kidney Diseases. Several authors disclosed funding support and honoraria for advisory board roles with various pharmaceutical companies, including Alnylam, which makes givosiran.
This article was updated 2/3/23.