Rare diseases: "We must isolate your child"

BarcelonaMisha was born on July 3, 2025. Six days later, on the 9th, his mother, Madona, received a call from Vall d'Hebron University Hospital in Barcelona requesting her admission. The heel prick test performed on her son at the hospital where he was born showed results that were confirmed shortly afterward: severe combined immunodeficiency (SCID). This disease is caused by a disorder of several genes that prevent the development of the immune system, responsible for fighting all kinds of infections. The first response is to isolate the patient. So Madona and her son went to live in a hospital room while they waited for Misha to receive the treatment that would cure him. He had to reach three months of age or weigh five kilos. "I was with him in the hospital the whole time until they were able to perform a transplant. It was very hard, although Dr. Andrea Martín's medical team made everything very easy for us," Madona recalls. Severe combined immunodeficiency (SCID) is one of the many and diverse rare diseases that exist, and this Saturday, February 28th, is the day commemorated. "A disease is considered rare when it affects fewer than one in 2,000 individuals. It's a small part of the population, but precisely for that reason, extra effort must be dedicated to dissemination, so that affected families can have the option of consulting the appropriate referral centers and so that the country's healthcare centers are prepared to care for these patients, with complex conditions that affect..." says a pediatrician and member of the Pediatric Infectious Diseases and Immunodeficiencies Unit (UPIIP) at the Vall d'Hebron University Hospital.

Bubble Kids

Small patients with severe combined immunodeficiency are known as bubble kidsSince they must be kept safe from potential infections from the time this condition is detected until they can begin treatment, "This disease means that, if not diagnosed in time, the child can develop a serious infection during the first months of life, whether viral or due to an opportunistic microorganism, which can lead to death before their first birthday. If they survive the infection, however, curative treatment has a worse prognosis due to Mar." Currently, there are two treatments that allow these children to achieve an optimal immune system: hematopoietic stem cell transplantation (from bone marrow, peripheral blood, or umbilical cord blood) and, in some selected cases, gene therapy.

Since 2017, cases have been detected in Catalonia bubble kids thanks to newborn screening, the heel prick testThis allows for diagnosis before infections appear. In fact, the first case wasn't cured until 2019. Bubble Boy Detected with the heel prick test in Catalonia. "Before this test, some children were cured, but the survival rate only reached 43%. It was a low rate because they were only diagnosed if there was a family history or when a serious infection was detected and they were admitted to the ICU," says Martín. Now, after the process—which before the transplant involves administering medication and chemotherapy sessions, followed by a reasonable waiting period until the immune system is reconstituted—and if there are no complications, patients can be discharged from the hospital when they are five months old. "If the baby arrives at the transplant without any prior infection and with the organs fully preserved, the success rate of the process reaches 95% and the cure is complete."

Severe combined immunodeficiency is estimated to be more frequent in populations where there is consanguinity. As Martín explains, in our country we have a very low rate of consanguinity, at 3%, and an average of between 53,000 and 60,000 births per year. "The incidence of severe combined immunodeficiency in Catalonia is one newborn per 40,000. So it is estimated that one or two cases appear each year."

Once a week at the hospital

Misha was three months old when they were able to perform the transplant. "Fortunately, everything went very well. Now we only go to the hospital once a week for checkups and blood tests, but it seems his immune system is improving every day," says Madona happily, although she knows it will still be a while before her son can start living a completely normal life. The heel prick test they performed on him right after he was born was key.

Rare diseases involve multiple organs and affect the physical capabilities, mental abilities, and sensory and behavioral qualities of those affected. They can appear from birth or childhood, but some do not manifest until adulthood. "They are very diverse and affect a very small number of patients, which leads to a certain complexity in diagnosis. The evolution of genetic studies, which are becoming increasingly complex, and with advanced technologies, means that more and more patients with rare diseases are being recognized and diagnosed, and it is even possible to ensure their prevention," adds Martín. At the Vall d'Hebron University Hospital, there are more than 200 specialist professionals dedicated to the care of more than 40,000 patients with rare diseases. It is one of the hospitals in Spain that treats the most pathologies and one of the leading centers in Europe in this field. It is part of the European Reference Networks (ERNs) for rare diseases, which guarantees that it can offer all treatments to patients, such as gene therapies or thymus transplantation, even those suffering from ultra-rare diseases.