In 2003, workers building a highway through a small township in Ireland chanced upon a long-lost medieval graveyard.

Of the roughly 1,300 bodies found at the site near the township of Ballyhanna, a couple of the ancient interred stood out. Their bones were riddled with benign tumors caused by a rare disease, but for strangely different reasons.

Both of the individuals appeared to have a genetic condition known as multiple osteochondromas, which causes painful yet typically non-malignant tumors to grow in bone, leading to limb deformity, postural issues, or nerve damage over time.

Today we know the disease is far from common, occurring on a roughly one in 50,000-person basis. Finding two bodies with the condition in such a small graveyard is quite the coincidence, especially since a genome analysis on the remains published in the European Journal of Human Genetics finds the two men who left the bones weren't closely related.

In fact, their lives in this small Irish parish were separated by several centuries.

"We made several assumptions about these two men when we first realized that they both had suffered from multiple osteochondromas," explains archaeologist Eileen Murphy from Queen's University Belfast, a senior author on the study.

"We assumed they were contemporary but radiocarbon dating showed they were separated by several hundred years. We also assumed they were related but the new [ancient DNA] analysis has demonstrated that this is not the case."

None of the skeletons unearthed at the Ballyhanna's lost graveyard look like they were in particularly good health when they died. Some show evidence of tuberculosis or rickets.

But the bones of the two men with bony outgrowths were in particularly poor health.

Archaeologists suspect the graveyard was once part of a lower class Gaelic medieval community that included men, women, and children. Some individuals were probably very poor, while others worked as farmers, laborers, merchants, artisans, or clergy.

The discovery of two unrelated men with the same rare bone disease in such a small community is unusual in itself, and it gets even stranger.

Despite their similar appearances, the recent analysis revealed the two cases of multiple osteochondroma weren't even caused by the same genetic mutation.

The individuals both showed changes in the EXT1 gene, which has been linked to multiple osteochondromas. But one of the mutations has never been seen in modern patients.

The first man had a missense mutation in a part of his EXT1 gene, whereby a single nucleotide base was swapped for another, scrambling the encoded sequence for the protein. It has been previously identified in at least three modern patients with multiple osteochondromas.

The second man showed a premature stop message in the same gene that has not yet appeared in modern sequencing data of patients with the disease.

The individual with the novel mutation died at a younger age, around 18 to 25, and showed deformities in his hips, knees, ankle, and forearm. He lived sometime between 1031 and 1260 CE.

The individual that died at an older age, around 30 or 40, had less pronounced tumors but they were evident throughout his skeleton. He lived between 689 and 975 CE.

"It was really surprising that these individuals had completely different mutations causing their condition, especially because it's so rare," says geneticist and first author Iseult Jackson from Trinity College Dublin.

The discovery just goes to show how much modern DNA analysis can reveal about diseases that have been with us for millennia.

"The study demonstrates the important contribution that ancient DNA analysis on people from the past can make to understanding conditions that still affect people today," says Trinity College Dublin geneticist, Dan Bradley.

The study was published in the European Journal of Human Genetics.