A cherubic baby lay on a pristine white sheet, breaking into a fantastic grin at his mother. She leaned forward and gave him a little peck on his forehead. Eugene, a five-month-old infant, had been a mother’s dream—full of smiles, contentment, and easy to care for. The young mother had been full of bliss since he was born, but today she looked worried and sad.

A few days ago, Eugene’s mother received a call that broke her heart. At the other end of the telephone was a doctor from a nearby hospital. He told her, in a measured tone, that little Eugene had just been diagnosed with a rare hereditary disease that caused muscle weakness and atrophy. He would eventually lose the ability to walk and breathe before his second birthday. Her mind went numb at that point, and the rest of the conversation was little more than sounds flowing in and out of her consciousness. The doctor said something bleak about the prognosis but promised her that he would do what he could. She was suddenly at a loss for words, and tears started rolling down her once joyful face.

Eugene’s condition is called Spinal Muscular Atrophy (SMA), which is the most common inherited cause of infant mortality. More than one child in a family may be afflicted, even though the parents do not exhibit any physical aspects of the genetic condition. Two physicians, Guido Werdnig and Johann Hoffman, made the first attempt to lift the veil of this mysterious infantile syndrome in the 1890s, but another century would pass before a major breakthrough was made. In the 1990s, scientists discovered that SMA is caused by a defective or missing gene that produces the human survival motor neuron (SMN) protein. This SMN protein is like sunlight to plants. Without it, muscle in the patient’s body is destined to wilt and die. In the most serious cases, infants rarely see their second birthday.

Thanks to the intensive research on the human genome, there is today a sophisticated understanding of the structure of the SMN gene and how it operates in our body. As scientists tweak and synthesise genes in a laboratory, gene therapy has emerged as a promising treatment option for patients like Eugene. It works by delivering the functional gene to cells at a rate large enough to replace the wrong copy, thus enabling the body to produce enough SMN protein for itself. Figuratively speaking, the process is akin to marshalling thousands of billions of tiny soldiers and arming them each with an identical code book and a map. Once injected into the body, these soldiers each make a long and winding march towards their assigned target cell while dodging the sentries of the body’s defence systems. Their mission continues inside the cell, with the soldiers slipping their code books through the cellular fence and letting out a loud cry to summon the cell to produce SMN protein.

A few weeks after the devastating news, Eugene’s mother received another call from the same doctor. Her heart pounded as she listened intently. “I want to let you know that there is a clinical trial going on for an experimental therapy,” said the doctor, “and this would offer hope to little Eugene’s situation.” He went on to say something about gene therapy, DNA loaded cells, target delivery and genome editing that the mother did not quite understand. But through teary eyes, she saw a gleam of hope.

Eugene was enrolled in the clinical trial of this experimental treatment in 2014, where he was given a single infusion directly into his vein in a hospital. It was a nerve-wracking moment, and his parents were at his bedside throughout the whole procedure, praying that the tiny soldiers inside the milky liquid would find their way and do their job.

A few days passed, and Eugene seemed well. The doctor indicated that Eugene’s tiny body was responding positively. Fifteen other patients below the age of two also underwent the first series of trials, which went on for over three years. The outcome was very promising, with the children’s muscle functions preserved if not much improved.

This novel therapy has revolutionised treatment to address previously unmet medical needs and has since benefited thousands of young SMA sufferers like Eugene in more than 40 countries. It is a milestone more than 130 years in the making, made possible by generations of dedicated researchers who left no stone unturned in studying the disease. With researchers redoubling their efforts in using this pioneering method for cure, other debilitating genetic abnormalities might eventually become a thing of the past, like the silent tears that Eugene’s mother once shed.