Exploring the therapeutic potential of CRISPR/Cas9 for the treatment of PelizaeusMerzbacher Disease

ASHG 2018 Annual Meeting – research using mouse models

Guest post by Eleonora Maino (ASHG poster: Wednesday 2-3pm, poster number 1107)

Pelizaeus Merzbacher Disorder (PMD) is a rare X-linked pediatric leukodystrophy, that
affects approximately 1:100,000 children at birth. The disease is associated with severe
motor and cognitive impairment and a limited life expectancy. PMD is caused by mutations
in the PLP1 gene, encoding proteolipid protein 1, one of the main components of myelin. In
healthy individuals, myelin forms an insulating layer around the nerve fibers allowing fast
and efficient signal conduction in the nervous system. Mutations in the PLP1 gene interrupt
this process, leading to the hallmark symptoms of PMD. While a variety of mutations can
lead to PMD, the vast majority of cases are the result of duplications of the X chromosome
region containing the PLP1 gene. Currently, there is no cure and treatment options are
limited to symptom management, which fail to have any considerable impact on the quality
of life or lifespan of PMD patients. Accordingly, there is an urgent need for the development
of effective therapies for PMD patients.

Since the discovery of the novel genome editing technology CRISPR/Cas9, a variety of
innovative strategies have been developed to correct genetic defects, including genome
rearrangements such as duplication mutations. Here, we are implementing a
CRISPR/Cas9-based approach to remove the Plp1 duplication and ameliorate disease
manifestation in a PMD mouse model, with the eventual goal of providing a new treatment
strategy not only for PMD, but for all genetic disorders caused by genomic duplications.
To date, we have characterized a PMD mouse model containing a Plp1 duplication
generated in the laboratory of Dr. Grace Hobson. This mouse model is an excellent model
to test CRISPR/Cas9 strategies in vivo since it recapitulates both PMD human mutations
and disease phenotypes.

To test the genome editing approach in vivo, we administered the CRISPR/Cas9
components via intracerebroventricular injection in the brain of newborn PMD pups, utilizing
adeno-associated viral vectors 9 (AAV9) as a delivery vector. Preliminary analyses suggest
that, 12 days after the injection, Plp1 expression both at the mRNA and protein level is
reduced in PMD mice treated with CRISPR/Cas9 compared to GFP injected control mice.
These data suggest that CRISPR/Cas9 promoted the removal of the Plp1 duplication in the
treated mice. Next, we will optimize the treatment and assay for a potential attenuation of
disease phenotypes.

Once completed, this project will provide the essential in vivo proof of concept to further
develop the CRISPR/Cas9 system as a therapeutic option for PMD patients, opening a
novel potential avenue for the treatment of genetic disorders caused by genomic
duplications.

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