KLKB1 and prekallikrein deficiency: 1986). Kallikrein then cleaves both low- and high-molecular-weight kininogens to release bradykinin and lys-bradykinin, mediating the effects of the KKS (Sainz et al. 2007). Recessively inherited mutations in KLKB1 are known to cause plasma prekallikrein deficiency, resulting in a prolonged activated partial thromboplastin time (aPTT) without increased bleeding tendency in affected patients (Lombardi et al. 2003). Heterozygous patients have been reported to have decreased prekallikrein activity but normal aPTT values (Wynne Jones et al. 2004).