Her two-year-old son William was diagnosed with the cruel, degenerative disease type two spinal muscular atrophy in June last year.

He has since lost the ability to walk and crawl and, without treatment, would eventually lose the ability to breath, swallow and talk.

The only effective treatment, Nusinersen (brand name Spinraza), has been millions of dollars out of reach as it is not listed on the Pharmaceutical Benefits Scheme.

Ms Taylor and partner Ben McLennan have been forced to watch their son deteriorate every day, despite knowing a treatment was available that could slow his symptoms.

Late last year, the drug was knocked back by Pharmaceutical Benefits Advisory Committee (PBAC) - which advises the government on what drugs to place on the PBS - over concerns of its cost-effectiveness.

But the family's heartache turned into unexpected elation on Friday when they found out PBAC had recommended the drug be listed on the PBS at its most recent meeting.

William will be eligible to access the drug from May when the company makes it available on compassionate grounds until the government places it on the PBS.

Health Minister Greg Hunt has previously guaranteed that if the PBAC recommends it, the government will list the drug.

In a surprise decision, PBAC decided to recommend the drug for listing on the PBS for type one, two and three (a) patients, despite the fact that drug company Biogen had only made submissions for access for type one patients.

“We were just elated, it felt like we had won all the lotteries and all the Powerballs,” Ms Taylor said.

“An absolute dream come true, I was in tears.

“All we want for our son ultimately is for him to have a good quality of life and independence.

"We know we have a big journey ahead of us now."

Children with type one SMA - the most serious form of the disease - have had access to the drug on compassionate grounds since last year with many seeing astounding results.

But for type two patients - whose life expectancy ranges from childhood to early adulthood depending on severity - there was no way to access the drug without paying.

Spinal Muscular Atrophy Incorporation chief executive officer Julie Cini said this meant some type one children were surpassing the milestones of type two diagnosed children.

"This announcement by the PBAC, is a phenomenal outcome, especially as Biogen was asked to resubmit to the March meeting for SMA Type 1 only," she said.

"When SMA Australia representatives were invited to the stakeholder meeting in January we highlighted the unmet need for urgent cases outside Type 1 and we asked the PBAC to consider those families as well.

"We would like to acknowledge the PBAC for inviting our community to the meeting and for listening to our voices that day on behalf of the whole community."

But the drug will remain out of reach for SMA patients over the age of 18.

"SMA Australia realise this part of our community will be devastated," Ms Cini said.

"Due to the infancy of the drug, and lack of robust clinical data, the PBAC was unable to assess the extent of the meaningful benefit the drug may have on the adult population."

Ms Taylor said the family would continue to spread awareness of SMA and advocate for the drug to be made available to over 18s.