The Hereditary Transmission of Congenital ‘True’Hypoprothrombinaemia

SUMMARY. The family pedigrees of three patients with congenital ‘true’hypoprothrombinaemia are reported. By means of a specific prothrombin assay three groups of patients could be separated, namely: homozygote, heterozygote and normal. The one‐stage factor II level in the homozygotes varied between 9% and 16%. Similar levels were obtained by means of other prothrombin assays. The prothrombin level in the heterozygotes varied between 43% and 75% (average 58.1·9.7). The prothrombin level in the normal relatives of the homozygote patients varied between 84% and 130% (average 96.7·10.2). The prothrombin level in a group of normal subjects unrelated to the homozygotes varied between 86% and 115% (average 98.0·7.9). These data are compatible with the assumption that the disorder is transmitted as an autosomal incompletely recessive trait. The heterozygotes are usually asymptomatic but may have epistaxis, excessive bleeding after tooth extraction and menorrhagia.