- Doctors in the United Kingdom have used a revolutionary gene therapy to cure a toddler who has a rare genetic disorder—called MLD—that is usually fatal.
- At £2.87 million ($3.42 million), the treatment is the most expensive therapy ever approved for use in the U.K.’s National Health Service.
- The therapy, marketed as Limeldy, can only save children who have yet to develop symptoms of the disease.
- Therefore, doctors and families affected by this condition are calling for all children to be screened for MLD at birth.
Children who inherit a rare genetic illness called metachromatic leukodystrophy (MLD) experience a progressive loss of their ability to think, move, and sense the world around them.
They eventually become unable to walk, swallow, speak, hear, see or respond to stimuli.
Most children who develop the infantile form of MLD
Around one in 100 people carry the faulty gene that causes MLD. However, the gene in question is “recessive,” which means that only children who inherit a faulty copy from both of their parents will develop the condition.
As a result, MLD is rare and affects only around one in 40,000 babies born in the U.K..
Estimates suggest that fewer than 50,000 people in the United States have the disease.
The gene for MLD makes a defective version of an enzyme. The job of the healthy enzyme, known as arylsulfatase A (ARSA), is to break down fatty substances called sulfatides in the white matter of the brain and spinal cord.
Sulfatides are a vital component of myelin, which is the fatty sheath that protects and insulates nerve cells.
In children with two copies of the defective gene, however, excessive amounts of sulfatides accumulate in the myelin sheath, which disrupts the nerves’ activity and causes inflammation.
Dr. Simon Jones, who treats children with MLD at Royal Manchester Children’s Hospital in Manchester, U.K., says that a mistake in a gene prevents the body from making an enzyme.
“The job of that enzyme is to…
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