rs1064793792 — SERPING1

SERPING1 c.856del — A Frameshift That Silences C1-Inhibitor

The SERPING1 gene encodes C1-inhibitor (C1-INH)¹¹ C1-inhibitor (C1-INH)
Serpin family G member 1 — a serine protease inhibitor that circulates in the blood and is the primary brake on the complement and contact activation pathways, the body's frontline inflammatory response systems. C1-INH keeps these systems from running uncontrolled. When C1-INH is absent or non-functional, the contact activation pathway generates bradykinin — a potent peptide that opens blood vessel walls and drives fluid into surrounding tissues. The result is hereditary angioedema (HAE): unpredictable, recurrent episodes of severe swelling affecting the skin, gut, and airway.

The c.856del variant removes a single cytosine nucleotide at position 856 of the SERPING1 coding sequence, causing a frameshift that alters every amino acid from position 286 onward and almost certainly triggers nonsense-mediated mRNA decay — destroying the transcript and producing no C1-INH protein from that allele. This is the molecular signature of HAE Type I, the most common form. HAE affects approximately 1 in 50,000 people globally²² 1 in 50,000 people globally
Fisch et al. 2025 systematic review; prevalence 0.13–1.6 per 100,000 across regions, with no significant difference between ancestries.

The Mechanism

C1-INH is the dominant inhibitor of factor XIIa and plasma kallikrein³³ factor XIIa and plasma kallikrein
the two key enzymes of the contact activation pathway that ultimately produce bradykinin from kininogen as well as complement proteases C1r and C1s. When one SERPING1 allele carries a frameshift, circulating C1-INH levels fall to approximately 30–50% of normal — insufficient to fully suppress kallikrein activity. Bradykinin surges drive episodes of submucosal and subcutaneous edema⁴⁴ submucosal and subcutaneous edema
Non-pitting swelling in the deep dermis and submucosa, not at the skin surface — which is why antihistamines and corticosteroids, which target mast-cell-driven superficial edema, are ineffective in HAE. Attacks commonly affect the face, hands, feet, genitalia, and gastrointestinal tract (abdominal pain mimicking a surgical emergency), and the larynx — where swelling can obstruct the airway within hours.

HAE follows autosomal dominant inheritance⁵⁵ autosomal dominant inheritance
One mutant allele is sufficient to cause disease — the remaining functional allele cannot compensate for the 50% reduction in C1-INH. Each child of an affected parent has a 50% chance of inheriting the mutation. Even first-degree relatives with no personal history of swelling should be tested. De novo mutations occur in approximately 20–25% of cases, so a negative family history does not rule out the diagnosis.

The Evidence

The mortality data from HAE are stark. A landmark study by Bork et al.⁶⁶ Bork et al.
Journal of Allergy and Clinical Immunology, 2012 — 728 patients across 182 families found that 70 of 214 deceased patients died from asphyxiation during laryngeal attacks. Among those who died from asphyxiation, 63 had never received a diagnosis of HAE — they lived on average 31 years shorter than HAE patients who died from other causes. The systematic review by Guan et al.⁷⁷ Guan et al.
Orphanet Journal of Rare Diseases, 2024 — 65 studies, 10,310 patients quantified the overall asphyxiation mortality risk at 8.6%, with a mean diagnostic delay of 3.9 to 26 years. This diagnostic gap is where most preventable deaths occur.

The mutation spectrum of SERPING1 is broad. A Spanish cohort study by López-Lera et al.⁸⁸ López-Lera et al.
Molecular Immunology, 2011 — 59 families identified 52 distinct mutations, of which 15 (29%) were frameshifts. Frameshift mutations virtually always abolish protein production entirely (Type I HAE), in contrast to some missense mutations that allow secretion of a non-functional protein (Type II HAE). The clinical phenotype across frameshift mutations is similar — the specific nucleotide deleted matters less than the consequence: absent C1-INH.

Modern therapies have transformed HAE management. The HELP trial⁹⁹ HELP trial
Riedl et al., Allergy, 2020 — lanadelumab subcutaneously every 2–4 weeks showed 85.7–100% of patients achieved a ≥50% attack reduction compared to 26.8% on placebo, with 37.9–48.1% becoming completely attack-free. The APeX-2 trial¹⁰¹⁰ APeX-2 trial
Zuraw et al., JACI, 2021 — berotralstat 150 mg daily showed an oral agent reduced attacks from 2.35 to 1.31 per month (P<0.001). For acute attacks, icatibant¹¹¹¹ icatibant
Cicardi et al., NEJM, 2010 — FAST-1/2 trials (a bradykinin B2 receptor antagonist) reduced time to symptom relief to 2.0–2.5 hours compared to 4.6–12.0 hours for control, making it a reliable on-demand treatment.

Practical Actions

For carriers of this mutation, the primary priority is an accurate diagnosis followed by access to on-demand acute treatment — carried at all times — and an individualized prophylaxis plan. Laryngeal attacks follow a predictable progression: a predyspnea phase averaging 3.7 hours, then a dyspnea phase averaging 41 minutes, then rapid deterioration. Treatment must begin in the predyspnea phase. First-degree relatives should be tested regardless of symptom history — asymptomatic carriers can develop their first severe attack at any age, and attacks are frequently triggered by surgery, dental procedures, stress, estrogen-containing contraceptives, or infection.

Estrogen-containing medications (oral contraceptives, hormone replacement therapy) can precipitate and worsen HAE attacks by reducing C1-INH levels further and increasing bradykinin production. Women with this mutation should specifically avoid estrogen-containing preparations and discuss progestogen-only or non-hormonal alternatives with their physician.

Interactions

HAE attacks can be triggered or worsened by ACE inhibitors — drugs used for blood pressure and heart failure — because ACE normally degrades bradykinin, and ACE inhibition allows bradykinin to accumulate. HAE patients receiving this mutation result should review all current medications with their treating allergist or immunologist, as several drug classes interact meaningfully with the bradykinin pathway.