Hereditary Angioedema as a Metabolic Liver Disorder: Novel Therapeutic Options and Prospects for Cure

Normalization of C1 Inhibitor in a Patient with Hereditary Angioedema

Hereditary angioedema is a potentially life-threatening autosomal dominant condition, causing attacks of angioedema due to failure to regulate bradykinin. Nearly all cases of hereditary angioedema are caused by mutations in the gene encoding C1 inhibitor, SERPING1. C1 inhibitor is a multifunctional protein produced in the liver that regulates the kallikrein-kinin system at multiple points. An infant with genetically confirmed hereditary angioedema and low C1 inhibitor levels (but without previous episodes of angioedema) underwent liver transplantation for biliary atresia, an unrelated condition. Liver transplantation led to normalization of the C1 inhibitor level and function. To our knowledge, this represents the first patient to be potentially cured of hereditary angioedema.

Clinical Progress in Hepatic Targeting for Novel Prophylactic Therapies in Hereditary Angioedema

Hereditary angioedema (HAE) is typically caused by a deficiency of the protease inhibitor C1 inhibitor (C1INH). The absence of C1INH activity on plasma kallikrein and factor XIIa leads to overproduction of the vasoactive peptide bradykinin, with resulting angioedema. As the primary site of C1INH and prekallikrein production, the liver is recognized as an important therapeutic target in HAE, leading to the development of hepatic-focused treatment strategies such as GalNAc-conjugated antisense technology and gene modification. This report reviews currently available data on hepatic-focused interventions for HAE that have advanced into human trials. Donidalorsen is an investigational GalNAc3-conjugated antisense oligonucleotide that binds to prekallikrein mRNA in the liver and reduces the expression of prekallikrein. Phase 2 data with subcutaneous donidalorsen demonstrated a significant reduction in HAE attack rate compared with placebo. Phase 3 trials are underway. ADX-324 is a GalNAc3-conjugated short-interfering RNA being investigated in HAE. BMN 331 is an investigational AAV5-based gene therapy vector that expresses wild-type human C1INH and is targeted to hepatocytes. A single intravenous dose of BMN 331 is intended to replace the defective SERPING1 gene and enable patients to produce functional C1INH. A first-in-human phase 1/2 study is ongoing with BMN 331. NTLA-2002 is an investigational in vivo clustered regularly interspaced short palindromic repeats/Cas9-based therapy designed to knock out the prekallikrein-coding KLKB1 gene in hepatocytes; a phase 1/2 study is ongoing. Findings from these and other ongoing studies are highly anticipated with the expectation of expanding the array of treatment options in HAE.

The Rapidly Expanding Genetic Spectrum of Common Variable Immunodeficiency-Like Disorders

The understanding of common variable immunodeficiency disorders (CVID) is in evolution. CVID was previously a diagnosis of exclusion. New diagnostic criteria have allowed the disorder to be identified with greater precision. With the advent of next-generation sequencing (NGS), it has become apparent that an increasing number of patients with a CVID phenotype have a causative genetic variant. If a pathogenic variant is identified, these patients are removed from the overarching diagnosis of CVID and are deemed to have a CVID-like disorder. In populations where consanguinity is more prevalent, the majority of patients with severe primary hypogammaglobulinemia will have an underlying inborn error of immunity, usually an early-onset autosomal recessive disorder. In nonconsanguineous societies, pathogenic variants are identified in approximately 20% to 30% of patients. These are often autosomal dominant mutations with variable penetrance and expressivity. To add to the complexity of CVID and CVID-like disorders, some genetic variants such as those in TNFSF13B (transmembrane activator calcium modulator cyclophilin ligand interactor) predispose to, or enhance, disease severity. These variants are not causative but can have epistatic (synergistic) interactions with more deleterious mutations to worsen disease severity. This review is a description of the current understanding of genes associated with CVID and CVID-like disorders. This information will assist clinicians in interpreting NGS reports when investigating the genetic basis of disease in patients with a CVID phenotype.

SERPING1 Variants and C1-INH Biological Function: A Close Relationship With C1-INH-HAE

Hereditary angioedema with C1 Inhibitor deficiency (C1-INH-HAE) is caused by a constellation of variants of the SERPING1 gene (n = 809; 1,494 pedigrees), accounting for 86.8% of HAE families, showing a pronounced mutagenic liability of SERPING1 and pertaining to 5.6% de novo variants. C1-INH is the major control serpin of the kallikrein–kinin system (KKS). In addition, C1-INH controls complement C1 and plasminogen activation, both systems contributing to inflammation. Recognizing the failed control of C1s protease or KKS provides the diagnosis of C1-INH-HAE. SERPING1 variants usually behave in an autosomal-dominant character with an incomplete penetrance and a low prevalence. A great majority of variants (809/893; 90.5%) that were introduced into online database have been considered as pathogenic/likely pathogenic. Haploinsufficiency is a common feature in C1-INH-HAE where a dominant-negative variant product impacts the wild-type allele and renders it inactive. Small (36.2%) and large (8.3%) deletions/duplications are common, with exon 4 as the most affected one. Point substitutions with missense variants (32.2%) are of interest for the serpin structure–function relationship. Canonical splice sites can be affected by variants within introns and exons also (14.3%). For noncanonical sequences, exon skipping has been confirmed by splicing analyses of patients' blood-derived RNAs (n = 25). Exonic variants (n = 6) can affect exon splicing. Rare deep-intron variants (n = 6), putatively acting as pseudo-exon activating mutations, have been characterized as pathogenic. Some variants have been characterized as benign/likely benign/of uncertain significance (n = 74). This category includes some homozygous (n = 10) or compound heterozygous variants (n = 11). They are presenting with minor allele frequency (MAF) below 0.00002 (i.e., lower than C1-INH-HAE frequency), and may be quantitatively unable to cause haploinsufficiency. Rare benign variants could contribute as disease modifiers. Gonadal mosaicism in C1-INH-HAE is rare and must be distinguished from a de novo variant. Situations with paternal or maternal disomy have been recorded (n = 3). Genotypes must be interpreted with biological investigation fitting with C1-INH expression and typing. Any SERPING1 variant reminiscent of the dysfunctional phenotype of serpin with multimerization or latency should be identified as serpinopathy.

Hereditary Angioedema Post-liver Transplant

Liver transplantation is the standard of care in managing different types of liver disorders as well as a variety of inborn errors of metabolism. In the latter scenario, the liver-based enzyme abnormality is corrected by transplantation. Although rare, liver transplantation may result in the transmission of an inborn error of metabolism to the recipient. The present report describes the development of acquired hereditary angioedema likely following liver transplantation, with notable improvement with the initiation of C1 esterase inhibitor replacement therapy. This case report describes another example of a hepatic synthesis defect that, although rare, but can be acquired from donor's livers.

Genetic variants of SERPING1 gene in Polish patients with hereditary angioedema due to C1 inhibitor deficiency

Hereditary angioedema due to C1-inhibitor deficiency (C1-INH-HAE) type I and II is a rare and life-threatening disease caused by SERPING1 gene mutations. Previous genetic studies indicated a wide spectrum of disease-associated variants in the SERPING1 gene and often lack of correlation with patient’s phenotypes. The aim of this study was to evaluate the presence, type, and localization of mutations in the SERPING1 gene in 41 Polish patients with C1-INH-HAE and their relation with case/family history, type of C1-INH-HAE, fC1-INH, age of onset, and disease severity. Sanger sequencing and MLPA method were used for detection of disease-associated variants. In 34 (82.9%) patients, mutations located in various regions of SERPING1 gene were revealed. The detected alterations in patients with C1-INH-HAE type I differed and were positioned in various exons/introns of the SERPING1 gene. The most frequent disease-associated variants appeared in exon 3 (especially in type I) and in exon 8 (type I and II). Out of 20 different disease-causing variants, 9 were not previously described. We did not find any relation between the type and location of the mutations and no type of features included in phenotype evaluation of the patients, such as case and family history, type of C1-INH-HAE, age of onset, biochemical parameters, or severity of disease.

Hereditary angioedema in children and adolescents - A consensus update on therapeutic strategies for German-speaking countries

BACKGROUND/METHODS

At a consensus meeting in August 2018, pediatricians and dermatologists from German-speaking countries discussed the therapeutic strategy for the treatment of pediatric patients with type I and II hereditary angioedema due to C1 inhibitor deficiency (HAE-C1-INH) for Germany, Austria, and Switzerland, taking into account the current marketing approval status. HAE-C1-INH is a rare disease that usually presents during childhood or adolescence with intermittent episodes of potentially life-threatening angioedema. Diagnosis as early as possible and an optimal management of the disease are important to avoid ineffective therapies and to properly treat swelling attacks. This article provides recommendations for developing appropriate treatment strategies in the management of HAE-C1-INH in pediatric patients in German-speaking countries. An overview of available drugs in this age-group is provided, together with their approval status, and study results obtained in adults and pediatric patients.

RESULTS/CONCLUSION

Currently, plasma-derived C1 inhibitor concentrates have the broadest approval status and are considered the best available option for on-demand treatment of HAE-C1-INH attacks and for short- and long-term prophylaxis across all pediatric age-groups in German-speaking countries. For on-demand treatment of children aged 2 years and older, recombinant C1-INH and bradykinin-receptor antagonist icatibant are alternatives. For long-term prophylaxis in adolescents, the parenteral kallikrein inhibitor lanadelumab has recently been approved and can be recommended due to proven efficacy and safety.

Review: Diagnosing Common Variable Immunodeficiency Disorder in the Era of Genome Sequencing

Common variable immunodeficiency disorders (CVID) are an enigmatic group of often heritable conditions, which may manifest for the first time in early childhood or as late as the eighth decade of life. In the last 5 years, next generation sequencing (NGS) has revolutionised identification of genetic disorders. However, despite the best efforts of researchers around the globe, CVID conditions have been slow to yield their molecular secrets. We have previously described the many clinical advantages of identifying the genetic basis of primary immunodeficiency disorders (PIDs). In a minority of CVID patients, monogenic defects have now been identified. If a causative mutation is identified, these conditions are reclassified as CVID-like disorders. Here we discuss recent advances in the genetics of CVID and discuss how NGS can be optimally deployed to identify the causal mutations responsible for the protean clinical manifestations of these conditions. Diagnostic criteria such as the Ameratunga et al. criteria will continue to play an important role in patient management as well as case selection and sequencing strategy design until the genetic conundrum of CVID is solved.

Clinical Implications of Digenic Inheritance and Epistasis in Primary Immunodeficiency Disorders

The existence of epistasis in humans was first predicted by Bateson in 1909. Epistasis describes the non-linear, synergistic interaction of two or more genetic loci, which can substantially modify disease severity or result in entirely new phenotypes. The concept has remained controversial in human genetics because of the lack of well-characterized examples. In humans, it is only possible to demonstrate epistasis if two or more genes are mutated. In most cases of epistasis, the mutated gene products are likely to be constituents of the same physiological pathway leading to severe disruption of a cellular function such as antibody production. We have recently described a digenic family, who carry mutations of TNFRSF13B/TACI as well as TCF3 genes. Both genes lie in tandem along the immunoglobulin isotype switching and secretion pathway. We have shown they interact in an epistatic way causing severe immunodeficiency and autoimmunity in the digenic proband. With the advent of next generation sequencing, it is likely other families with digenic inheritance will be identified. Since digenic inheritance does not always cause epistasis, we propose an epistasis index which may help quantify the effects of the two mutations. We also discuss the clinical implications of digenic inheritance and epistasis in humans with primary immunodeficiency disorders.