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For years, families in a small Brazilian town watched their children slowly lose the ability to walk—and no one knew why.
In Serrinha dos Pintos, tucked deep in the northeast of Brazil, kids would grow up like any others. But by the time they reached their teens, something began to change. Their legs weakened. Some others could barely move their arms.
Families had no idea why it was happening. Generation after generation, the same heartbreaking pattern repeated itself with a growing sense of worry that something was wrong.
Then came Silvana Santos.
A biologist and geneticist from São Paulo, Santos first arrived in the village more than 20 years ago. What started as a small investigation slowly turned into something much bigger—years of research, DNA samples, and interviews with dozens of families.
Eventually, she pieced it all together. The mystery illness had a name: Spoan syndrome.
Caused by a genetic mutation, the syndrome gradually affects the nervous system, weakening the body over time and in most cases, the person becomes fully dependent by their 50s.
Santos’s discovery was groundbreaking. It marked the first time this disease had ever been identified anywhere in the world. And for the people of Serrinha dos Pintos, it changed everything.
“She gave us a diagnosis we never had. After the research, help came: people, funding, wheelchairs,” said Marquinhos, one of the patients, speaking to the BBC.
So what exactly is Spoan syndrome, and why has it affected so many people in this one Brazilian town? Here’s a closer look.
Serrinha dos Pintos: ‘A world of its own’
When Silvana Santos first arrived in Serrinha dos Pintos, she said, it was like stepping into “a world of its own” – not just because of the lush scenery and mountain views, but also because of how closely connected everyone was.
The more she walked and spoke with locals, the more surprised she was at how common marriages between cousins were. The town of over 5000 people has stayed fairly isolated for generations, with little movement in or out. As a result, cousin marriages are socially accepted and remarkably common.
A 2010 study led by Santos revealed that more than 30 per cent of couples in Serrinha were related by blood. And among those couples, one-third had at least one child living with a disability, according to the BBC.
To put it in perspective, globally, cousin marriages account for around 10 per cent of all unions—but the numbers vary wildly. In countries like Pakistan, the rate is above 50 per cent. In contrast, it’s less than 1 per cent in places like the US and Russia. In Brazil overall, it’s between 1–4 per cent.
While most children born to cousins are completely healthy, geneticists point out that the risk of passing on rare inherited disorders nearly doubles when both parents share the same DNA background.
“If a couple is unrelated, the chance of having a child with a rare genetic disorder is about 2–3 per cent. For cousins, the risk rises to 5–6 per cent per pregnancy,” explained Luzivan Costa Reis, a geneticist at the Federal University of Rio Grande do Sul.
“In Serrinha dos Pintos, deep down, we’re all cousins. We’re related to everyone,” says 25-year-old Larissa Queiroz, who married her distant relative. She said that she and her husband, Saulo, only discovered their common ancestor after several months of dating.
A gene game
What started as a simple research trip for Silvana Santos quickly became a mission that would span years.
She drove the 2,000 kilometres from São Paulo to Serrinha dos Pintos more times than she could count—knocking on doors, collecting DNA samples, sitting down with families over coffee, and slowly piecing together the puzzle.
By 2005, her team published the first scientific paper describing Spoan syndrome. It was a breakthrough.
The cause? A tiny deletion on one chromosome leads to the overproduction of a key protein in brain cells. Over time, that imbalance begins to break down the body’s nervous system.
But what fascinated researchers even more was just how old the mutation seemed to be, possibly dating back centuries, long before the town itself had even formed.
When scientists looked closer at the DNA of Spoan patients, they found strong European ancestry: Portuguese, Dutch, and Sephardic Jewish roots.
That theory gained weight when two people in Egypt were also diagnosed with Spoan. Their DNA showed the same genetic markers as the cases in Brazil.
“It likely came with related Sephardic Jews or Moors fleeing the Inquisition,” Santos told the BBC. She also believes there could be more undiagnosed cases out there—possibly in Portugal and beyond.
So far, 82 cases have been identified across the world.
Is there a cure?
There’s no cure for Spoan—not yet. But Santos’ research has helped shift public understanding. Where once children with the condition were labelled “cripples,” people now speak of them with clarity and compassion. They’re simply said to have Spoan, reports BBC.
Today, Santos is part of a government-backed initiative that will screen 5,000 couples across Brazil for recessive genetic diseases.
The project, supported by the Ministry of Health, isn’t aimed at stopping cousin marriages. Instead, it’s about giving families the knowledge to make informed choices.
Now a university professor, Santos is still pushing for better genetic testing and education, especially in Brazil’s underserved northeast, where stories like Serrinha’s are still unfolding.
With input from agencies