Renowned biologist Silvana Santos credits her groundbreaking genetic discovery entirely to chance—she encountered a family affected by an unknown disease right on her own street.

Her research led to the identification of Spoan syndrome (spastic paraplegia, optic atrophy, and neuropathy), a rare genetic neurodegenerative disorder that causes progressive paralysis in north-eastern Brazil.

Over the past 20 years since beginning her work in the town of Serrinha dos Pintos, Santos has assisted residents living with the condition in obtaining vital diagnoses. She focuses on studying the prevalence of rare genetic diseases and their connection to consanguineous marriages in impoverished rural communities of Brazil.

More than two decades ago, before Silvana Santos came to the small town of Serrinha dos Pintos, its residents were unaware of the cause behind the widespread loss of walking ability among their children. Situated in northeastern Brazil, this remote community of fewer than 5,000 people became the place where biologist and geneticist Santos discovered and named a previously unrecognized condition: Spoan syndrome. This syndrome, resulting from a genetic mutation, impacts the nervous system and leads to a gradual weakening of the body. It only manifests when the mutated gene is inherited from both parents.

Prior to Santos's arrival, families were left without any understanding of the illness impacting their children. Now, the local community discusses Spoan and genetics with assurance. "She provided a diagnosis we had never received before. Following the research, support arrived: people, funding, wheelchairs," recalls Marquinhos, one of the patients. Years of dedicated investigation enabled Santos and her research team to recognize these symptoms as part of Spoan syndrome. They eventually discovered 82 additional cases around the world.

Serrinha's geographical isolation and little inward migration mean that many of the population are related, making marriage between cousins far more likely and more socially acceptable. Worldwide, marriages between relatives were estimated at around 10% in the early 2010s. More recent data shows the rate varies widely, from over 50% in countries like Pakistan, to 1-4% in Brazil and less than 1% in the US and Russia. Most children born to pairs of cousins are healthy, experts say. But these marriages do face a higher risk of a harmful genetic mutation being passed down through the family. A 2010 study led by Santos showed that more than 30% of couples in Serrinha were related, and a third of them had at least one child with a disability.

While advancements toward a cure have been limited, monitoring patients has led to noticeable improvements. Rejane remembers a time when individuals were labeled "cripples." Today, they are respectfully identified as having Spoan. The introduction of wheelchairs has not only provided greater independence but also helped avoid deformities—previously, many affected were left lying in bed or on the floor without support.

Santos’s work was the first global description of the disease, and in recognition of this and her ongoing contributions, she was honored as one of the BBC's 100 most influential women in 2024.