British scientist Charles Darwin's episodes of sickness were at times completely disabling. (Associated Press)

An Australian scientist believes he has identified what caused Charles Darwin's long-standing illness.

Associate Prof. John Hayman from the University of Melbourne's anatomy department believes Darwin probably had cyclical vomiting syndrome, which he inherited from his mother.

His findings appear in the Christmas issue of the British Medical Journal.

"People with cyclical vomiting syndrome experience abdominal, circulatory, and cerebral symptoms, including headaches and anxiety," writes Hayward.

For most of his adult life, Darwin suffered from very long bouts of seasickness that would continue after his voyages.

Symptoms included nausea, vomiting, headaches, stomach pain, "inordinate flatulence" and skin problems, including eczema and boils.

"The episodes of sickness were at times completely disabling and Darwin was confined to his sofa in a constant nauseated state for days — even weeks — at a time," writes Hayman.

Excitement or stress — even from pleasurable events, such as seeing old friends — would bring on the illness.

Darwin tried many different treatments but none of them had a lasting effect.

Diagnoses galore

Darwin was diagnosed as having all manner of psychological illnesses from hypochondria, neurasthenia, panic disorders, agrophobia and even "repressed anger towards his father," nervousness about his relationship with his wife and guilt over conflict with earlier religious beliefs.

Physical diagnoses include Meniere's disease, arsenic poisoning and Chagas disease from a South American insect bite.

Hayward says all of these can be dismissed for good reasons and the more accurate diagnosis is cyclical vomiting syndrome (CVS).

"Although this is primarily a disease of children it may persist into adult or may appear for the first time in adulthood," he writes.

"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."

"Darwin's mother Susannah died with abdominal pain when he was eight," writes Hayward.

'Never quite well'

"As a child she had vomiting and boils, experienced motion sickness, had excessive sickness during pregnancies, and 'was never quite well.' "

Apparently her younger brother Tom also had similar symptoms.

"Evidence of a matrilineal inheritance pattern is good, consistent with an abnormality of mitochondrial DNA," writes Hayward.

"Darwin was not aware of mitochondria or of genes and genetic mutations, but he was very much aware of random variations within species," he concludes.

"His personal inherited genetic variation made him substantially 'less fit,' but his survival prospects were greatly increased by his driving intellect, loyal colleagues, a devoted wife, family and household servants and his personal wealth."