An article appeared recently in BioNews announcing the first-ever approval of an RNA-based therapy for use on the British National Health Service.
The name of the drug is Patisiran for the treatment of hereditary transthyretin-mediated amyloidosis (hATTR). Patisiran decreases the potency of the protein transthyretin (TTR) found primarily in the liver.
About hATTR Amyloidosis
hATTR amyloidosis belongs to a group of diseases caused by the buildup of deposits in the body called amyloids. A different misfolded protein is responsible for each type of amyloidosis.
Symptoms of the disease can begin at any time between the age of twenty to seventy. However, if the disease is severe, life expectancy may not exceed fifteen years. There are approximately one hundred patients with hATTR in the UK and fifty thousand patients worldwide.
A gene change (mutation) affects the function of the TTR protein which is produced almost entirely in the liver. Although amyloid protein is found in many parts of the body, they occur most often in the peripheral nervous system (PNS) outside of the spinal cord and brain.
The PNS connects the central nervous system to sensory cells and muscles involving sound, pain, touch, and heat. hATTR patients experience loss of sensation in limbs and have issues with involuntary functions such as blood pressure, digestion, and heart rate.
Leptomeningeal is a type of hATTR that involves the central nervous system. It occurs in leptomeninges (tissue covering the spinal cord and brain).
A protein buildup in the leptomeninges results in:
- Bleeding or fluid accumulating inside the brain
- Weakness and muscle stiffness
- Difficulty in the coordination of movements
Patisiran works by silencing a gene, but it does not change the patient’s DNA. The drug interferes with genes that produce damaging proteins. It decreases TTR.
The drug utilizes RNA interference as a way to inactivate “messenger” RNAs that make copies of the mutated gene. These messengers (mutated genes) act as a guide for the creation of the mutated protein.
The cost of Patisiran (£300,000 a year) is a concern for many physicians and patients. The drug must be administered intravenously once every three weeks.
Clinical studies have proven that Patisiran is able to stop and even improve some of the debilitating symptoms of hATTR. In a recent clinical trial with 225 treated participants, Patisiran was responsible for a 56 percent improvement in symptoms as compared to 4% of participants who received a placebo. A 36-month follow-up found that these numbers were maintained.
The scientific community is encouraged by the trial results and is looking forward to working with eligible patients to create a better quality of life for them. Their goal is to develop gene-silencing drugs that will prolong the lives of patients with rare diseases.