American Journal of Hematology 46:234-240 (1994) z Moderate Hemophilia B Leyden: Identification by Polymerase Chain Reaction, Sequencing, and Oligomer Restriction Thomas E. Coyle, Timothy Spicer, Doris Michalovic, and Bernard J. Poiesz Department of Medicine, Division of Hematology Oncology SUNY Health Science Center at Syracuse, Syracuse New York (T.E.C., zy T.S., B.J.P.); The Southern Tier Hemophilia Center, Johnson City, New York (D.M.) Hemophilia B Leyden is a rare form of congenital factor IX deficiency which is character- ized by severe factor IX deficiency at birth, which ameliorates after puberty. It is caused by mutations in the factor IX gene promoter region and the postpubertal amelioration is thought to be mediated by the action of testosterone on an androgen response element located in the promoter region. Three kindreds have been previously reported with a milder form of hemophilia B Leyden, associated with a guanine to adenine transition at nucleotide position -6 of the promoter region. We now report a fourth kindred with this mutation. The proband was a newborn with a factor IX level of 2.5%, his 12-year-old half-brother had a level of 28%, and his mother’s 56-year-old maternal cousin had a level of 60%. A G to A transition at nucleotide -6 of the promoter region was demonstrated by cloning and sequencing polymerase chain reaction products from the half brother, and the mother was demonstrated to be a carrier. The mutation eliminates a zyxw Tag1 restriction endonuclease site normally present in the wild type promoter, and the mother’s cousin was demonstrated to carry the mutation by the absence of digestion with Taql. The identification of hemophilia B Leydenwith this specific mutation has practical importance to the clinical management because of its unique natural history and significantly better prognosis than classical hemophilia B. Key words: hemophilia B Leyden, factor IX, promoter, polymerase chain reaction zyx o 1994 Wiley-Liss, Inc. INTRODUCTION zyxwvutsrq spontaneous hemarthrosis and having factor IX levels Hemophilia B is a congenital bleeding disorder which is caused by a functional deficiency of factor IX. It has classically been separated into two types; CRM-(cross reacting material negative), where immunologically de- tectable factor zyxwvutsrq IX protein is not produced, and CRM+, where immunologically detectable factor IX protein is produced, but the functional activity of the protein is decreased. When a patient is affected with hemophilia B, the level of factor IX activity will usually be constant throughout his life. Additionally, all affected members within a kindred will have approximately the same level of factor IX activity. The level of factor IX activity varies between kindreds, but not within kindreds or within indi- vidual patients. less than 1%. However, there were males in these kin- dreds who gave a clear history of abnormal bleeding in childhood that abated after puberty. These older males were found to have factor IX levels of approximately 3WO%. They did not identify any males in these kin- dreds whose bleeding tendency persisted into adulthood. All 27 patients from the original report could trace their ancestry back to a particular town in the Netherlands, and it was considered highly likely that they had inherited the disease from a common ancestor. These authors subse- quently followed the factor IX levels longitudinally in eight prepubertal males from this group who were se- verely affected [2]. Factor IX levels began to rise at the age of 15 or 16 years and continued to rise at a rate of In 1970, Veltkamp et al. [I] described a variant of Factor IX deficiency which does not adhere to this classi- Like B’ their patients had a sex linked recessive disorder, with affected having a severe bleeding tendency from the time of birth, suffering zyxwv 0 1994 Wiley-Liss, Inc. cal behavior, which they named hemophilia B Leyden. Received for publication July 19, 1993; accepted January 12, 1994. Address reprint requests to Dr. Thomas Coyle, Department of Medi- cine, SUNY Health Science Center at Syracuse, 750 East Adams St., Syracuse, NY 13210.