A remote Brazilian village where 'everyone is a cousin': Ground Zero for rare genetic disorder

Spoan syndrome is a genetic mutation that progressively weakens the nervous system (Image credit: BBC)

Children living in a small, remote town in northeastern Brazil were slowly losing the ability to move, and their parents had no clue what was causing it.

Kids in Serrinha dos Pintos used to experience normal growth during childhood, but things took a different turn when they reached their teens. Their legs weakened, and some could barely move their arms.

This pattern persisted generation after generation. It changed when Silvana Santos, a biologist and geneticist from São Paulo, began investigating this phenomenon. Years of research, DNA samples, and interviews with dozens of families led to a breakthrough.

She finally put all the pieces of the puzzle together and identified and named a  unknown condition as Spoan syndrome.

Let's have a closer look at this rare syndrome.

Decoding Spoan syndrome

The syndrome, caused by a genetic mutation, progressively affects the nervous system, weakening the body over time. In most cases, individuals become fully dependent by their 50s.

Santos's discovery was groundbreaking, marking the first time this disease had been identified anywhere in the world. For the people of Serrinha dos Pintos, it was life-changing.

“She gave us a diagnosis we never had. After the research, help arrived: people, funding, wheelchairs,” said Marquinhos, one of the patients, in an interview with the BBC.

Serrinha dos Pintos: ‘A world of its own’

When Silvana Santos first arrived in Serrinha dos Pintos, she described it as stepping into “a world of its own,” not just due to the stunning landscape, but because of the strong community bonds. She was struck by how common cousin marriages were, with the town, home to over 5,000 people, remaining isolated for generations.

A 2010 study by Santos found that more than 30% of couples in Serrinha were blood-related, and about one-third of their children had disabilities. While cousin marriages make up about 10% of unions globally, the rate varies widely. In countries like Pakistan, it exceeds 50%, while in the US and Russia, it’s below 1%. In Brazil, it’s between 1-4%.

Geneticists note that the risk of passing on rare inherited disorders is nearly doubled when both parents share the same DNA. “If a couple is unrelated, the chance of having a child with a rare genetic disorder is 2-3%.

For cousins, it’s 5-6%,” explained geneticist Luzivan Costa Reis. "In Serrinha dos Pintos, we’re all cousins,” says 25-year-old Larissa Queiroz, who married her distant relative Saulo. They only learned of their shared ancestry after months of dating.

A decade old genetic mutation

What began as a simple research trip for Silvana Santos turned into a mission that spanned years.

She repeatedly drove 2,000 kilometers from São Paulo to Serrinha dos Pintos, collecting DNA samples, talking to families, and piecing together the mystery.

In 2005, Santos and her team published the first scientific paper on Spoan syndrome, identifying a small genetic mutation that causes the overproduction of a protein in brain cells, slowly breaking down the nervous system. Researchers were fascinated to learn that the mutation could be centuries old, likely predating the town itself.

DNA analysis revealed that Spoan patients had strong European ancestry, including Portuguese, Dutch, and Sephardic Jewish roots.

This theory gained further credibility when two cases in Egypt were linked to the same genetic markers. Santos believes the mutation likely spread with Sephardic Jews or Moors fleeing the Inquisition, and she suspects more undiagnosed cases may exist globally, especially in Portugal.

So far, 82 cases of Spoan have been identified worldwide. What started as a three-month research trip evolved into years of dedication, with Santos eventually relocating to the region to continue her work.

Is cure possible? 

There is no cure for Spoan yet, but Santos' research has changed the way people view those affected. Once labeled "cripples," children with the condition are now understood with clarity and compassion.

Santos is now involved in a government-backed initiative to screen 5,000 couples across Brazil for recessive genetic diseases, providing families with the knowledge to make informed choices.

The project, supported by the Ministry of Health, does not aim to stop cousin marriages, but to empower families. As a university professor, Santos continues to advocate for better genetic testing and education, particularly in Brazil’s underserved northeast.