DNA Explainer: All about world's most expensive drug Zolgensma which costs Rs 18 crore a dose

Do you know which is the most expensive drug in the world and it is used to cure which disease? The drug's name is Zolgensma, manufactured by Swiss multinational pharmaceutical company Novartis.

The life-changing drug 'Zolgensma', considered the world's most expensive drug and approved by the United Kingdom's National Health Service (NHS) to cure a rare genetic disorder has gone viral. 

The drug with a reported list price of Rs18 crore per dose was first approved for use by the US and recently by the UK. 

This one-time gene therapy is used to treat babies with a type of severe spinal muscular atrophy. The condition causes muscle weakness and affects movement and breathing.

As per the website of the Organisation of Rare Diseases India, there are over 3,00,000 children with spinal muscular atrophy (SMA) but very little awareness and support.

Zolgensma drug was first approved by the US Food and Drug Administration on May 24, 2019.

With this, it became the first gene therapy approved to treat children less than two years of age with spinal muscular atrophy (SMA), the most severe form of SMA and a leading genetic cause of infant mortality.

The virus used in Zolgensma gene therapy works as soon as it is introduced to a patient, their body starts to produce antibodies.

If they have a second injection of the virus, it won't work as they will have developed an immunity to it and antibodies will fight against it. This means that only a single injection of the treatment can be effectively used.

What is spinal muscular atrophy?

SMA is a rare genetic disease caused by a mutation in the survival motor neuron 1 (SMN1) gene. The gene encodes the survival motor neuron (SMN) protein - a protein found throughout the body, which is critical for the maintenance and function of specialized nerve cells, called motor neurons. 

Motor neurons in the brain and spinal cord control muscle movement throughout the body. If there is not enough functional SMN protein, then the motor neurons die, leading to debilitating and often fatal muscle weakness. 

SMA caused by mutations in the SMN1 gene is generally classified into several subtypes, based on the age of onset and severity, infantile-onset SMA is the most severe and most common subtype.

Children with this condition have problems holding their head up, swallowing and breathing. These symptoms may be present at birth or may present by the age of 6 months.

How Zolgensma works?

Zolgensma is an adeno-associated virus vector-based gene therapy that targets the cause of SMA.

The vector delivers a fully functional copy of the human SMN gene into the target motor neuron cells.

Zolgensma uses harmless, genetically engineered viruses to increase SMN protein levels.

Upon injection into the blood (through 'intravenous injection'), the viruses are able to travel around the body.

It will get to a variety of different cells to help restore some of the SMN protein that is missing due to the condition.

Zolgensma is indicated for the treatment of children less than two years of age with SMA. 

The product is a one-time intravenous administration that results in the expression of the SMN protein in a child’s motor neurons.

Zolgensma is an SMN-enhancing therapy that works by replacing the missing or mutated SMN1 gene through a virus named AAV9.

This virus carries the replacement gene into the body. This virus 'infects' the cells with the new DNA.

This then improves muscle movement and function, and the survival of a child with SMA. 

Dosing is determined based on the weight of the patient.

Side-effects of Zolgensma

The most common side effects of Zolgensma are elevated liver enzymes and vomiting. Zolgensma has a boxed warning that acute serious liver injury can occur. 

Patients with pre-existing liver impairment may be at higher risk of experiencing a serious liver injury.