LIKE FATHER, LIKE SON: HEREDITARY ANGIOEDEMA (HAE) WITH LOW C1Q LEVELS

Abstract

<h3>Introduction</h3> Two types of HAE derive from deficiency or dysfunction of C1 inhibitor (HAE-C1-INH). Low C1q levels suggest acquired angioedema due to C1-INH deficiency (AAE-C1-INH). Rarely, HAE-C1-INH may also present with low C1q. <h3>Case Description</h3> A 33-year-old male presented with a 10-year history of episodic, severe abdominal pain. History was notable for extremity swelling occurring four times annually. Work-up revealed low C4 (<2 mg/dL), C1-INH (<3 mg/dL), functional C1-INH (5%), and C1q (4.4 mg/dL). Due to isolated angioedema in the fourth decade of life and no family history of angioedema with low C1q, AAE-C1-INH was considered. Evaluation for AAE-C1-INH-associated disorders, including an underlying B cell lymphoproliferative disorder, was negative. The patient was prescribed icatibant as abortive therapy. After these findings, the family requested testing for their 7-year-old son. Although the son did not have any overt episodes of swelling, he reported episodic globus sensation. Son's workup revealed low C4 (<2 mg/dL) and C1-INH (3 mg/dL). Functional C1-INH was unable to be interpreted due to lab error. These findings prompted us to consider the diagnosis of HAE-C1-INH with low C1q with plan to perform a genetic screening panel for angioedema. <h3>Discussion</h3> Clinically, AAE-C1-INH diagnosis is suggested in patients with low levels of C4, C1-INH, and C1q, especially if presenting in the fourth decade of life and without a familial history of angioedema. However, a recent study found 6 of 61 patients with HAE (9.8%) had low levels of C1q. Therefore, in cases with inconclusive AAE-C1-INH-associated disorders, HAE-C1-INH should still be considered.