Darwin's mitochondria

I’m always skeptical when pathologists attempt to diagnose the ills of historical figures. Even if there are medical records or abundant attestations of symptoms from contemporary sources, people in the past had different ways of describing the observations that doctors today collect.

But that doesn’t stop people from trying. Last month, John Hayman published a paper in the British Medical Journal that claims a new diagnosis for the lifelong malady that Darwin described in his own journals and correspondence:

Darwins symptoms are those of cyclical vomiting syndrome. Although this is primarily a disease of children it may persist into adulthood or may appear for the first time in adulthood. The disease is related to classic migraine and abdominal migraine but is also linked to abnormalities of mitochondrial DNA, with mutations in the MTTL1 gene. This disease is neither well known nor well recognised, particularly in adults, although it was first described in the English literature in 1882.
People with cyclical vomiting syndrome experience abdominal, circulatory, and cerebral symptoms, including headaches and anxiety. Symptoms overlap with those of classic and abdominal migraine, except for a lack of aura. Affected people may experience some or all of these symptoms, with each individual having similar symptoms with each episode. Over time, however, progression or change may occur in the most prominent feature, and episodes may coalesce. Many people report severe motion sickness, and this may be associated with a full episode.

It seems plausible enough, as much so as any retrospective diagnosis could probably be. It bears all the drawbacks of other attempts to diagnose historical figures.

A test of the hypothesis: mtDNA is maternally inherited and haploid, so symptoms are very likely to be shared by maternal relatives:

Darwins mother Susannah died with abdominal pain when he was 8. As a child she had vomiting and boils, experienced motion sickness, had excessive sickness during pregnancies, and "was never quite well." Her younger brother Tom had similar symptoms, with headaches, abdominal pains, and motion sickness. A sister, Sarah, considered that Charles and his uncle Tom had the same illness. Evidence of a matrilineal inheritance pattern is good, consistent with an abnormality of mitochondrial DNA.

It’s a sad thing to affect a family.

Mitochondrial disorders are increasingly recognized as causes of chronic disease – just the other day, a new study implicated defective mitochondria as causes of Parkinson’s Disease. I think it’s hilarious because there is a cadre of geneticists who depend on the notion that mtDNA is a neutral marker of population history.

Darwin’s DNA has nothing to say about whether it was neutral on an evolutionary timescale, but every famous mtDNA functional mutation reminds us that there is biological function there, which is a target of selection under some circumstances.

(via Why Evolution Is True)

References:

Hayman JA. 2009. Darwin's illness revisited. Br Med J 339:b4968. doi:10.1136/bmj.b4968