Personal Genetics Education Project

In the news: Potential new approach to gene therapy for sickle cell disease

Last week, research published in the journal Nature demonstrated an approach based on the hot new gene editing technology, CRISPR, that might one day be used to treat sickle cell disease (SCD). (“CRISPR Exploits Vulnerability of Sickle Cell Disease,” Genetic Engineering and Biotechnology News.)

SCD is a debilitating genetic disorder that affects millions worldwide, mostly those of African descent, and is caused by a mutated form of the oxygen-carrying hemoglobin (Hb) proteins in red blood cells (RBCs). The mutated Hb proteins bind together abnormally and cause RBCs to become sickle-shaped and rigid, get stuck in blood vessels and lead to excruciating pain.

In this study, a team led by Harvard scientists Stuart Orkin and Daniel Bauer and MIT biologist Feng Zhang used CRISPR to delete part of the regulatory DNA sequences for the gene BCL11A, which is responsible for “switching off” the fetal form of Hb. Normally, fetal Hb is active until a baby is about one year old, when the adult form of Hb kicks in and takes over. The SCD mutation occurs in adult Hb. So, by switching off the regulator that switches off fetal Hb, this functional form of Hb can be turned backed on in adults suffering from SCD.

While this study’s results are promising, much work will still need to be done before this approach can be safely used to treat SCD patients.

Currently, there is only one FDA-approved drug for SCD – hydroxyurea, a chemo drug that also works by increasing the number of RBCs with fetal Hb. Though hydroxyurea has led to good clinical outcomes, it doesn’t work for all SCD patients, and there are also some potential side effects when taken long-term. Another drug, which helps “unstick” the mutant Hb and prevent RBC sickling, is currently in clinical trial, while an experimental gene therapy that works by delivering a healthy copy of the Hb gene into the patient’s blood-making stem cells also reported positive results earlier this year.

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