Discussion
HAE is an uncommon autosomal dominant disorder characterized by recurrent episodes of subcutaneous oedema, reduced complement C4 and low antigenic and/or functional levels of C1-INH. HAE is a potentially life-threatening medical condition. Depending on the C1-INH antigenic and functional levels, HAE has been classified into 3 different types.7 In majority (80-85%) there is a reduction of both antigen and functional levels of C1-INH protein (type I HAE) and in 15-20% patients C1-INH antigen levels are normal or elevated but it is dysfunctional (type II HAE). A rare form of hereditary angioedema (HAE nlC1-INH) is characterized by normal levels and function of C1-INH protein. HAE nlC1-INH is most commonly caused by mutation of coagulation factor XII (F12 ) gene. Recent advances in the genetic studies have identified some new genes that are associated with HAE nlC1-INH. These include mutations in angiopoietin 1 gene (HAE-ANGPT1),plasminogen gene (HAE-PLG) and Kininogen-1gene.8,22–25 Acquired angioedema (AAE-C1-INH) has mostly been reported in association with drugs, autoimmune diseases and B-cell lymphoproliferative disorders.26 Patients with AAE have older age at onset (4th or 5th decades of life). These patients have low levels or abnormal function of C1-INH and low levels of C1q. The present study, however, focussed on patients with type I HAE.
Published literature on HAE from developing countries is very limited.13–19,27–29 To the best of our knowledge, no long-term follow-up studies are available from India, especially in children. Moreover, there are limited data on genetic profile of patients with HAE from developing countries including India. Studies conducted in China27 and Japan30reported that the incidence of HAE in Asian countries is less as compared to studies from Latin American and Western countries such as Brazil31, Hungary32, Denmark33 and Germany.34 However, precise epidemiologic figures are not available.35Table 3 shows an overview of published studies on type 1 and 2 HAE including few paediatric studies.12,27,30–34,36–46
Diagnosis of HAE can be easily made from the characteristic oedema and is supported by a positive family history. Low serum C4 level is a cost-effective method of screening for HAE.2,3 In our cohort, the characteristic swelling was present in all patients and low C4 levels were detected in all. It has, however, been reported that C4 levels may occasionally be normal in HAE.2,9,36Assessment of serum C1-INH level (antigenic and functional) helps in establishing an accurate diagnosis. All patients in the present study had low C1-INH antigen levels.
Median age at onset of symptoms was 6.25 years in the present study which is comparable with several other previously published studies (Table 3). Median age at the time of diagnosis was 12 years with median delay in diagnosis of 6.5 years. This is largely because of lack of awareness amongst primary care physician and most patients were initially managed elsewhere as allergic angioedema.
No definite triggers were discernible in most patients in the cohort except few patients who identified blunt trauma, psychosocial stress and exercise as potential triggers. Frequency of attacks were discernibly less during pregnancy in 2 patients in our study. One of these 2 patients was continued on TA prophylaxis and she had an uneventful pregnancy. The other patient experienced 2 first trimester abortions while she was on TA prophylaxis even though she had no episodes of angioedema during both pregnancies. Pregnancy has variable effect on the clinical course of HAE.47–49 Attenuated androgens are considered contraindicated during pregnancy and plasma derived C1-INH and TA are considered safe. Mental stress has also been reported to be an important trigger in these patients.7,50
There can be substantial inter-individual variation in the onset of symptoms of HAE, duration of symptoms, frequency of attacks and severity of symptoms. These differences can exist within the members of the same family as was the case in several of our patients. In the Hungarian cohort, the clinical attacks were found to be more severe in children who had earlier age of disease onset.32 Recurrent abdominal pain may be seen in 30-100% of patients with HAE.27,31,51 It may be the initial presenting symptom in 40-80% of children.16,52 In the presented study, 1/3rd of all patients reported having gastrointestinal symptoms. Patients with predominant abdominal symptoms may inadvertently be subjected to exploratory laparotomy.30 In one study, 3 patients presented with oedematous abdominal attacks as initial symptoms.32 One patient in the present cohort had a history of exploratory laparotomy for acute surgical abdomen, several years before he was diagnosed to have HAE.
Erythema marginatum could be an early manifestation of HAE and may precede a disease flare. It may easily be confused with urticaria and is more commonly reported in children and with type 1 and 2 HAE.7,53 Erythema marginatum was seen in 3 patient in the present series.
In children, the only recommended drugs for management of acute episode of HAE are C1-INH concentrate.7 Solvent detergent –treated plasma (SDP) or fresh frozen plasma (FFP) may be considered when C1-INH therapy is not available.7 As C1-INH concentrate is not readily available commercially in our country, we had to administer FFP in our patients with laryngeal oedema and patients showed prompt resolution of symptoms. FFP may be considered as on demand therapy in countries where C1-INH therapy is not easily available.21
Patients and their parents were explained about need of long-term prophylaxis and available treatment options. All patients opted for long term prophylaxis as effective on demand treatment is not available in India and access to FFP in emergency situations may not be always be possible. TA has favourable side effect profile when compared to attenuated androgens. However, studies carried out in the past have reported safety of attenuated androgens even in prepubertal children.7,50 In India, we do not have access to plasma derived C1-INH therapy. Therefore, we considered attenuated androgens (stanozolol) as the agent of choice for long term prophylaxis of HAE. Most patients in our cohort showed reduction in frequency and severity of HAE attacks with stanozolol prophylaxis. However, few patients continued to have disease flare and even severe airway obstruction requiring plasma therapy while they were taking stanozolol prophylaxis. It has been observed that attenuated androgens are more effective than TA.7 However, TA was considered an upfront therapy in several patients in the present study considering their side effect profile and these patients showed good response to therapy.
Patients with HAE are prone to develop disease flare and occasionally life-threatening laryngeal oedema during surgical procedures especially dental surgeries.7 Plasma derived C1-INH therapy is recommended to be used as short-term prophylaxis during these procedures. Use of attenuated androgens and FFP have also been suggested if C1-INH is not available.54,55 We successfully used stanozolol and FFP for short term prophylaxis in 2 patients in the present series.
Genetic profile of patients with HAE has been studied for the first time in India. We found mutations in the SERPING1 gene in 11 out of 20 families who were screened. Nine of these 11 families had a novel pathogenic variant in the SERPING1 gene. Missense mutations in exon 7 and 8 were the most common mutations in our cohort. Mutation spectrum in SERPING1 gene is quite heterogeneous and more than 450 mutations spread over the entire gene have been reported so far.33,56–59 Missense mutations have been reported to be the most common mutations in SERPING1gene.8,60–62 while some populations have reported that nonsense or frameshift mutations are most common.33 Missense mutations in exon 8 have also been reported to be the most common mutation in certain populations.60,61,63 Few authors have also reported a genotype-phenotype correlation and have shown that non-sense, frameshift and deletion mutations are associated with a more severe disease phenotype.56,64 However, several other authors have reported no genotype-phenotype correlation and have suggested that polymorphisms in bradykinin receptor or contact system proteins may be responsible for this phenotypic heterogeneity.33,60 In the present study, we observed no genotype-phenotype correlation. Family members with same mutations were noted to have wide variation in age of symptom onset and disease severity suggesting a variable penetrance.8
We did Sanger sequencing for all 8 exons of SERPING1 gene, however, 9 out of 20 families were not found to have any pathogenic variant. All these families had characteristic clinical manifestations of HAE with low C4 and low C1-INH. All except 2 of these patients also had suggestive family history. We could have missed mutations in the promoter region and deep-intronic regions of the SERPING1 gene in these patients. Recently a deep intronic novel pseudoexon activating mutation in the intron 6 of SERPING1 gene has been reported in a family with HAE.65 Therefore, some of the patients with HAE in this study may have this deep intronic mutation or a variant in the promoter region of the gene.