Activated partial thromboplastin time prolongation without hemorrhagic dienhesis: a study of a chinese family coexisting with hereditary KNG1 p.Arg240 mutation and --SEA/αα genotype thalassemia

High molecular weight kininogen (HK) deficiency is a rare autosomal recessive disorder caused by mutations in the KNG1 gene. This study reports a 66-year-old male Chinese patient who presented with significantly prolonged activated partial thromboplastin time (aPTT) and microcytic hypochromic anemia. Whole-exome sequencing revealed a homozygous nonsense mutation in exon 6 of the KNG1 gene (c.718 C > T, p.Arg240*) in the proband. This mutation results from a cytosine-to-thymine substitution, generating a premature termination codon that leads to truncated HK protein translation and loss of function. Additionally, genetic testing identified a concurrent heterozygous α-thalassemia --^SEAdeletion in the proband, located at 16p13.3 and encompassing the HBA2 and HBA1 genes. Pedigree analysis indicated that both the proband and his sister were homozygous for the KNG1 mutation and exhibited prolonged aPTT, whereas their children and some descendants were heterozygous carriers with normal coagulation function. Within the same family, all heterozygous carriers of the α-thalassemia --^SEAdeletion presented with microcytic hypochromic anemia. This study represents the first documented case of co-occurrence of a homozygous KNG1 p.Arg240* mutation and the --^SEAdeletion α-thalassemia.