||This novel mutation consists of a deletion of one Cytosine on exon 3 of the SERPING1 gene, resulting in a frameshift that leads to a stop codon 30 codons downstream the mutation. The mutation causes premature termination of C1-INH protein synthesis, in a way that it lacks the serpin domain essential for biological activity of the protein. Evaluation of 165 members of the family allowed us to establish that this mutation is the definitive cause of HAE in this family. Twenty-eight members of a single family with diagnosis of type I HAE presented the c.351delC mutation, including 5 assymptomatic individuals with low levels of C1-INH and C4, whereas 137 close relatives without HAE did not bear the mutation. To our knowledge, this is the largest family reported with data which strongly support a pathogenic role of a novel mutation of the SERPING1 gene in the development of HAE, and this study constitutes the first molecular analysis of HAE described in Latin America.