A drug that can extend the life of children and adults with spinal muscular atrophy (SMA) has been approved by the Therapeutic Goods Administration and is now commercially available.

Until now, sufferers of SMA had few options, and babies with the most severe form of the genetic disease, SMA1, deteriorated until they couldn't swallow and breathe – usually by nine months of age.

The new treatment, nusinersen (brand name Spinraza), works by causing the body to increase production of a protein called survival motor neurons, which is critical to the function of muscles.

It has been shown to extend and improve the life of babies with SMA1. It is unclear how much the drug will cost, although in the US it can cost $US750,000 ($978,000) for one course of treatment – five to six doses over the first year.