Hemophilia B is called Christmas disease after Stephen Christmas, a young boy from London who was the first patient formally diagnosed with the condition. The name has nothing to do with the holiday, though the timing of the landmark paper’s publication made for a memorable coincidence.
The Patient Behind the Name
In 1952, researcher Rosemary Biggs and her team at Oxford published a paper in the British Medical Journal describing a bleeding disorder that looked identical to hemophilia but behaved differently in laboratory tests. The paper focused on a five-year-old boy named Stephen Christmas, who became the index case for what they called “Christmas disease.” The article appeared in the December 27 issue of the journal, just two days after the holiday, which has fueled the common misconception that the name is seasonal.
What Biggs and her colleagues had discovered was that Stephen Christmas and several other patients were missing a completely different clotting protein than people with classical hemophilia. Until that point, doctors had lumped all hemophilia patients together, not realizing there were two distinct conditions. The paper’s title made the distinction explicit: “Christmas disease: a condition previously mistaken for haemophilia.” Stephen Christmas lived with the condition for decades before passing away on December 21, 1993.
How Hemophilia B Differs From Hemophilia A
Classical hemophilia (type A) involves a shortage of clotting factor VIII. Hemophilia B involves a shortage of a different protein, factor IX. Both factors work in the same chain reaction that forms blood clots, which is why the two conditions produce nearly identical symptoms and why doctors couldn’t tell them apart before specialized lab tests existed. The distinction matters because treatment requires replacing the specific missing factor.
Hemophilia A is roughly three and a half times more common. In the United States, hemophilia A occurs in about 1 in every 5,617 male births, while hemophilia B affects about 1 in every 19,283 male births. Recent studies suggest hemophilia B may actually produce a somewhat milder bleeding tendency than hemophilia A at comparable factor levels, challenging the older assumption that the two conditions are clinically interchangeable.
Why It Almost Always Affects Males
The gene for factor IX sits on the X chromosome. Males have only one X chromosome (paired with a Y), so a single defective copy of the gene is enough to cause the disease. Females have two X chromosomes, meaning a working copy on one can typically compensate for a faulty copy on the other. A mother who carries one defective copy has a 50% chance of passing it to each son, who would then have hemophilia B. Her daughters have a 50% chance of becoming carriers themselves.
What Happens in the Body
Factor IX is produced in the liver and plays a key role in the internal clotting pathway, the series of chemical reactions your body uses to seal damaged blood vessels. When factor IX is missing or deficient, the chain reaction stalls and the body can’t build a stable clot. Small cuts aren’t usually the main problem. The more serious issue is bleeding inside the body, particularly into joints and deep muscle tissue.
The knees, ankles, and elbows are the most commonly affected joints. Repeated bleeds into the same joint cause pain, swelling, and stiffness, and over time can destroy cartilage and lead to chronic arthritis. Bleeding into deep muscles can cause limbs to swell enough to compress nerves, producing numbness or pain. Bleeding in the throat or neck, while rarer, can become life-threatening by obstructing the airway.
Severity Depends on Factor IX Levels
Hemophilia B is classified into three levels based on how much working factor IX is circulating in the blood. Severe hemophilia B means factor IX activity is below 1% of normal. People with severe disease can experience spontaneous bleeding episodes without any obvious injury. Moderate hemophilia B falls between 1% and 5% activity, where bleeding typically follows minor trauma. Mild hemophilia B, with factor IX levels above 5%, may only cause excessive bleeding after surgery, dental work, or a significant injury. Some people with mild hemophilia B don’t discover they have the condition until an unexpected bleeding event later in life.
How Treatment Has Changed
For much of the 20th century, treatment options were limited to transfusions of whole blood or plasma. The 1970s brought a major shift with the development of concentrated factor IX products derived from donated plasma, allowing doctors to raise clotting factor levels more precisely and even use regular preventive infusions (prophylaxis) rather than just treating bleeds after they started. Recombinant factor IX, manufactured without human blood products, became available in the 1990s and eliminated the risk of blood-borne infections that had devastated the hemophilia community in earlier decades.
More recently, bioengineered versions of factor IX with extended duration in the body have reduced how frequently people need infusions. The most significant milestone came in late 2022, when the FDA approved the first gene therapy for hemophilia B. The treatment delivers a functional copy of the factor IX gene directly to liver cells, potentially allowing the body to produce its own clotting factor. For a condition first identified in a five-year-old boy seven decades ago, the trajectory from a mystery diagnosis to a one-time gene therapy represents a remarkable arc.