without treatment, unlikely to reach their second birthday. When, as a researcher in the 1990s, I became aware of the disease there were no treatments even on the horizon. Now there are two recently licensed drugs to treat this devastating affliction.
There is a catch, of course. One of these drugs, Zolgensma, which has just been made available to treat babies in the UK, has been called “the most expensive drug in the world”. At £1.79 million for a dose, that’s probably true.
Spinal muscular atrophy is caused by the loss of a gene called survival motor neurons 1 (SMN1), which carries the information needed to make a protein, also called SMN, that is needed by every cell in the body. While in other species losing the SMN1 gene would be fatal, humans have an extra gene (SMN2) that can partly compensate for its loss. But SMN2 can generate only a small amount of the necessary protein compared to SMN1. And while many cells and organs in the body seem able to function with this reduced supply, motor neurons responsible for sending messages from the brain to the muscles are exquisitely sensitive to low levels of SMN.
This causes the loss of muscular control that is the characteristic symptom of the disease – where, for example, babies with the most common spinal muscular atrophy, type 1, usually fail to reach the developmental milestones such as actively rolling, sitting or crawling that most of us, as parents, take for granted. Other, milder types of the disease appear later in childhood (types 2 and 3) or in young adults (type 4), and result in progressive loss of muscle function. Some adults with the disease, such as Michaela Hollywood, work to raise awareness of it.
As biologists we don’t understand why motor neurons are so sensitive to the reduction of SMN protein, largely because the protein has many different jobs within the cell which we don’t yet understand. treatment, unlikely to reach their second birthday. When, as a researcher in the 1990s, I became aware of the disease there were no treatments even on the horizon. Now there are two recently licensed drugs to treat this devastating affliction.
There is a catch, of course. One of these drugs, Zolgensma, which has just been made available to treat babies in the UK, has been called “the most expensive drug in the world”. At £1.79 million for a dose, that’s probably true.
Spinal muscular atrophy is caused by the loss of a gene called survival motor neurons 1 (SMN1), which carries the information needed to make a protein, also called SMN, that is needed by every cell in the body. While in other species losing the SMN1 gene would be fatal, humans have an extra gene (SMN2) that can partly compensate for its loss. But SMN2 can generate only a small amount of the necessary protein compared to SMN1. And while many cells and organs in the body seem able to function with this reduced supply, motor neurons responsible for sending messages from the brain to the muscles are exquisitely sensitive to low levels of SMN.
This causes the loss of muscular control that is the characteristic symptom of the disease – where, for example, babies with the most common spinal muscular atrophy, type 1, usually fail to reach the developmental milestones such as actively rolling, sitting or crawling that most of us, as parents, take for granted. Other, milder types of the disease appear later in childhood (types 2 and 3) or in young adults (type 4), and result in progressive loss of muscle function. Some adults with the disease, such as Michaela Hollywood, work to raise awareness of it.
As biologists we don’t understand why motor neurons are so sensitive to the reduction of SMN protein, largely because the protein has many different jobs within the cell which we don’t yet understand.
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