The genetics of porphyria

Image: Pixabay

As we’ve already discussed the genetics of one disease back in episode 14, I’d like to focus on another in the form of porphyria- most famously suffered from by George III. However, this is not an isolated case within his family. In fact, porphyria can be seen throughout the family across the centuries, as I discovered when reading two papers from 1968 and 1982 which focus on the ancestors and immediate family of the king. So what causes porphyria and how is it passed down?

Porphyria is actually a group of diseases, one of the main symptoms of which is an increased secretion of proteins called porphyrins into the urine of patients. Porphyrins can also build up in the liver, which may lead to impeded liver function and an elevated risk of liver cancer. Alternatively, the nervous system can be impacted, which may lead to attacks and hallucination.

In porphyria patients, there is a mutation for the enzyme which produces haem according to the British Liver Trust. For reasons I’ll discuss in a moment, I think that this may actually be referring to haemoglobin– a molecule inside your red blood cells which binds them and allows them to carry oxygen through the blood. Haemoglobin is one of the derivatives of porphyrins, which I believe may be why porphyrins then build up- after all, if haemoglobin can’t be produced correctly, it seems logical that the products from the previous step should build up. For this reason, I believe that the ‘haem’ in the British Liver Trust article may refer to haemoglobin, as stated in the Encyclopaedia Britannica.

Most types of porphyria are inherited in an autosomal dominant fashion, meaning that only one copy of this allele needs to be inherited for symptoms to manifest- which might explain how it symptoms kept cropping up in the family shown below. However, there are rarer versions which are recessive, meaning that both copies of the gene need to be faulty before symptoms manifest.

So, that’s porphyria. As an interesting aside, there’s a 2011 article in the New Scientist which mentions that one sufferer is likely to have been Vlad Dracula, which may have started the idea that vampires can’t abide sunlight. In cutaneous porphyria, areas of the skin exposed to sunlight can become blistered. Afflicted individuals consequently avoid sunlight due to pain. Moreover, their skin may shrink back around the mouth, leading to the impression of fangs. I’m not going to go into it article here, but it’s certainly interesting to think that a disease suffered from by kings through the ages may have led to modern ideas about vampires.

Leave a Reply

Your email address will not be published. Required fields are marked *