Haemophilia in European royalty

Haemophilia figured prominently in the history of European royalty in the 19th and 20th centuries. Britain's Queen Victoria, through two of her five daughters (Princess Alice and Princess Beatrice), passed the mutation to various royal houses across the continent, including the royal families of Spain, Germany and Russia. Victoria's son Prince Leopold, Duke of Albany suffered from the disease. For this reason, haemophilia was once popularly called "the royal disease". Tests of the remains of the Romanov imperial family show that the specific form of haemophilia passed down by Queen Victoria was probably the relatively rare Haemophilia B.

The sex-linked X chromosome disorder manifests almost entirely in males, although the gene for the disorder is located on the X chromosome and may be inherited from the mother for male children or from either mother or father for female children. Expression of the disorder is much more common in males than in females. This is because, although the trait is recessive, males only inherit one X chromosome, from their mothers. Thus if the haemophilia gene is transmitted on it, there is no possibility for the male to inherit a haemophilia-free gene from his father to mask or dilute the symptoms. By contrast, a female who inherits a gene for haemophilia on one of her X chromosomes will also have inherited a second X chromosome from the other parent which is likely to carry a haemophilia-free gene that would prevent full expression of symptoms.

Females who inherit the gene for Haemophilia A or B from both parents would be expected to manifest full symptoms, similar to those seen in affected males, but this is extremely rare. Despite frequent inter-marriage among royalty, no case of such double inheritance is known among Queen Victoria's descendants. This is largely because only one of the individuals with Hemophaelia had any children.

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