KLKB1 and Congenital prekallikrein deficiency: Congenital prekallikrein deficiency is a rare autosomal recessive condition associated with mutations of the KLKB1 gene.21 In a 2020 study, Barco et al analyzed 111 individuals with prekallikrein deficiency, the largest cohort to date.23 The authors estimated the prevalence of severe prekallikrein deficiency to be 1/155,668 overall and 1/4,725 for individuals of African ancestry.