The new drug will reduce the burden of the disease among patients and their families, according to the authority.

“The current treatments include an injection to the spine that needs to be received every three to four months in a hospital,” Simon Tang Yiu-hang, the authority’s director of cluster services, said. “Another treatment is a daily tablet.

“With this new treatment, patients only need a single injection and do not need to be hospitalised regularly. I believe this is very helpful for patients and their families.”

SMA patients are born with a mutation of the SMN1 gene, which leads to SMN protein deficiency, according to Benjamin Lee Shing-cheung, the authority’s chief pharmacist. Consequently, the central nervous system becomes unable to regulate voluntary muscle movement and strength, resulting in gradual muscle weakness.

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The new drug will inject the gene into patients to produce such protein and help them function normally.

Research had shown that this treatment would increase life expectancy, Lee said, stressing that the best time to receive it was during infancy.

“Even when patients have been diagnosed in primary stages, this treatment will make obvious improvements to their mobility and reduce the need for permanently using a ventilator,” he said.

The toddler who was diagnosed with SMA type 1 at two weeks old received the treatment late in November, said Sophelia Chan Hoi-shan, a paediatrician at the Hong Kong Children’s Hospital and the boy’s head doctor.

The boy was selected to undergo the new treatment at the Children’s Hospital after he showed promising results upon receiving the traditional medication, Chan said.

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SMA is one of the most serious muscular diseases among children, with more than 80 per cent of patients dying before they reach the age of two due to quickly deteriorating conditions. According to Chan, they fail to sit upright and need ventilators to help them breathe.

Although the treatment, priced at US$2.1 million, is self-financed by patients, the authority has listed it under the Community Care Fund Assistance Programme for those in need.

The authority also planned to expand the use of this treatment to cover infants under the age of one, especially those six months or younger.

The boy’s mother said her son had shown significant improvements two weeks after doctors administered the drug. Both of their identities were not revealed over privacy concerns.

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“It was a nightmare when we heard about his diagnosis, but we are so grateful to the team for giving him the chance to try this treatment,” she said, hoping that her son would grow up strong and healthy and treasure his life.

“His physical abilities may develop slower, but it is okay, we will be with him every step of the way,” the mother added.