A woman has died from a rare form of dementia decades after she is thought to have caught the disease from her own baby while pregnant.
Her husband died of sporadic Creutzfeldt-Jakob disease two decades ago - but her own genes were previously shown to be clear of the responsible mutation, reports the Daily Mail.
However, the unidentified woman, from Denmark, died of the same crippling disease as her late husband while in her seventies.
Her son, whose identity has also been withheld but is known to be 53 and a father himself, is now "showing symptoms" of sporadic CJD.
Doctors now believe the son inherited the mutated gene responsible for the disease from his father, before passing it back to his mother while in the womb.
Cells from the foetus that contained the toxic proteins are thought to have traveled across the placenta into her bloodstream, before lodging in her brain.
The fatal condition causes irreversible brain damage, triggered by abnormal proteins known as prions, which gradually destroy brain cells.
The rare case was uncovered by a team of medics at the Danish Reference Centre for Prion Diseases in Copenhagen University Hospital.
The woman was diagnosed with sporadic CJD before the disorder was linked to her late husband or son.
CJD occurs due to abnormal proteins known as prions, which cause nerve-cell damage.
Prions can occur spontaneously, be inherited or transmitted on contaminated surgical equipment.
There is no cure.
Treatment focuses on relieving symptoms and making sufferers comfortable via painkillers and antidepressants.
Ausrine Areskeviciute, one of the medics who stumbled across the case, told The Times that it is a "very sad story".
She said: "We already know that when a woman is pregnant cells from the baby travel across the placenta and travel around her body, lodging in various organs.
"However, in this case the foetus carried the mutation for the misfolded proteins, and its cells may also have had misfolded proteins when they got into the mother's body."
Ms Areskeviciute added this may have triggered the process that led to her death years later.
The case of CJD, which is considered to be a type of dementia, was published in the Journal of Neuropathology & Experimental Neurology.
CJD, of which there are four main types, is a prion disease, which derives its name from "protein" and "infectious".
It is defined by proteins in the nervous system taking on an unusual shape, which then spread in a domino-like effect to cause lesions in the brain.
Some 85 per cent of cases occur randomly, while 10-15 per cent are inherited. In less than one per cent of incidences, CJD is acquired.
Mad cow disease is also a prion condition, which occurs when a person eats meat from cattle affected by a similar disease.
Sporadic CJD affects as little as one in a million people each year in the UK, NHS figures state.
This comes after research released earlier this year suggested prion diseases can be spread during operations via poorly-cleaned surgical equipment.
What is Creutzfeldt-Jakob Disease?
Creutzfeldt-Jakob disease (CJD) is a rare, fatal condition that causes irreversible brain damage.
Symptoms, which worsen rapidly over time, include:
Loss of intellect and memory
Loss of balance and co-ordination
Vision problems and blindness
Abnormal jerky movements
Loss of mobility
Most sufferers die within a year of symptom onset, usually due to an infection caused by immobility.