A novel RNA splice site mutation in the C1 inhibitor gene of a patient with type I hereditary angioedema.

We describe a patient with type I hereditary angioedema presenting recurrent episodes of skin swelling and abdominal pain. Laboratory examination showed reduced levels of CH50 and C4 with a normal C3 level. The C1 inhibitor was decreased to 7.0 mg/dl (normal, 10-25 mg/dl) with a remarkably reduced activity (<25%; normal, 80-125%). DNA analysis of the C1 inhibitor gene revealed a novel point mutation at the 3' acceptor mRNA splice site of the intron 5 (G-->A at nucleotide 8722). This mutation may abolish the correct splicing of the intron 5 and create unstable mRNA.