A genetic technique called allelic discrimination — which detects a specific variant of the F12 gene — might make diagnosing certain hereditary angioedema-causing mutations quicker and cheaper, a new study showed.
Titled “A cost-effective algorithm for diagnosis of hereditary angioedema with normal C1 inhibitor: applying molecular approach to clinical practice,” the study was published in The Journal of Allergy and Clinical Immunology: In Practice.
Hereditary angioedema (HAE) is usually caused by mutations in the gene SERPING1, which encodes a protein called C1-inhibitor (C1-INH). However, some people with HAE have no SERPING1 mutations and normal amounts of C1-INH. These patients can be a challenge to diagnose, with frequent high costs and delays.
The most common non-SERPING1 cause of HAE is mutations in the F12 gene. This gene provides the instructions for a protein called coagulation factor XII — coagulation factors are a group of related proteins essential for normal blood clotting. In particular, an F12 mutation referred to as c.983C>A is relatively common in HAE.
In this study, the researchers tested a new method for the detection of c.983C>A mutations, called allelic discrimination. The basic idea is that a sample of the patient’s DNA is tested with a probe that will only bind to the DNA if the mutation is present — essentially flagging mutations but not normal genes.
The method was tested on 184 people with family histories of HAE. The participants were predominantly female (73.9%) and ranged in age from two months to 91 years, with a median age of 35 years.
In addition to allelic discrimination, the patients’ DNA was assessed by Sanger sequencing – a method for determining the sequence of a gene and, by extension, the presence of any mutations. Sanger sequencing is often used as a “gold standard” for mutation detection.
Among the 184 participants, 96 (52%) tested positive for the c.983C>A F12 mutation using allelic discrimination. Sanger sequencing confirmed this in all 96 cases.
Further, the researchers calculated that carrying out allelic discrimination on one individual’s sample cost about $91.08 (USD) and took about six hours. In contrast, Sanger sequencing for one sample cost $496.69 and took 38.5 hours.
If 10 samples were processed simultaneously, allelic discrimination would cost $194.37 and take 7.5 hours, while Sanger sequencing would cost $776.28 and take 43.5 hours.
“Allelic discrimination was more cost-effective, with reduction of 82% in costs, and decrease of 84% in performance time, compared to Sanger sequencing,” the researcher concluded.
Based on these findings, the researchers proposed that patients who present with suspected HAE, but have normal C1-INH levels, should be referred for genetic testing via allelic discrimination as the first-line genetic test. Sequencing, which is lengthier and more costly, would then be needed only if allelic discrimination testing results are inconclusive, the researchers said.
Importantly, the method can be easily adapted to identify other mutations, making it amenable to broader screens than just c.983C>A in F12.