GeneE | Treatment for Prader-Willi Syndrome Using Adeno-Associated Viruses and CRISPR-Cas9 Machinery

by Ryan Fue

Coauthors: Acknowledgment Thank you to Dr. Anthony Chang and Dr. Sharief Taraman for giving me this opportunity to explore the medical field and broaden my understanding of medicine through the MI3 2021 Summer Internship Program. Additionally, thank you so much to Dr. Flannery for providing guidance and supporting me throughout the development of this abstract idea. I am forever grateful. References https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4231876/ https://www.nationalgeographic.org/encyclopedia/viruses/ https://medlineplus.gov/genetics/condition/prader-willi-syndrome/#inheritance https://www.science.gov/topicpages/f/facile+lentiviral+vector https://pubmed.ncbi.nlm.nih.gov/23057501/#:~:text=Families%2Fmothers%2Fsiblings%20with%20children%20with%20PWS%20reported%20difficulties%20in,an%20increased%20number%20of%20conflicts https://medlineplus.gov/genetics/understanding/therapy/genetherapy/ https://pwsavic.org.au/information/how-is-prader-willi-syndrome-diagnosed https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4449422/ https://news.unchealthcare.org/2020/10/scientists-take-major-step-toward-angelman-syndrome-gene-therapy/

Genomic & Precision Medicine

Background
Prader-Willi syndrome (PWS) is a complex genetic condition affecting approximately 1 in 10,000 to 30,000 people worldwide and causes a variety of debilitating conditions. While it is unclear, studies suggest these symptoms are caused by a loss of a group of snoRNA genes, known as the SNORD116 cluster from the paternity inherited chromosome region 15q11-13. Currently, there is no cure for PWS and those afflicted are often treated through specific treatments based on their symptoms. Unfortunately, oftentimes when prenatal children are diagnosed with Prader-Willi syndrome, they are aborted.

Method
GeneE is a method that aims to treat prenatal and perinatal children inflicted with Prader-Willi syndrome because of deleted gene segments in chromosome 15 through gene therapy, a technique that includes replacing mutated genes that cause disease with healthy copies, inactivating mutated genes, and introducing new genes into the body to treat disease. This method relies on early recognition of Prader-Willi syndrome in a prenatal or perinatal child through a variety of potential tests such as Noninvasive Prenatal Screening (NIPS), a FISH (fluorescence in-situ hybridization) test which can only identify PWS by deletion, or the methylation test which is the preferred method because it tests for all causes of PWS but requires the use of other methods to determine the exact cause. If PWS is found positive, DNA will be extracted from both the child and the father. In the approximately 70 percent of PWS cases resulting from deleted segments of the paternal chromosome 15, the GeneE method proposes to sequence the chromosome region 15q11-13 of the child to determine the area affected by the deletion. Once identified, the same section as the section affected by the deletion in the child’s DNA will be extracted from the father’s DNA. The method will then use CRISPR-Cas9 machinery and a modified adeno-associated virus (AAV) to deliver the Cas9 protein into the brain of the child to insert the father’s genes into the location of the deletion in the child’s. Relating back to the early recognition of PWS, when using this method it is vital to insert the vector as soon as possible as a higher vector to cell ratio enhances the efficiency of gene delivery, a naïve immune system allows for the induction of “tolerance” for the vector, reduces chances of an immune system response as the fetus is unlikely to have had previous viral infections and prevents pathology from manifesting enhancing the effectiveness of this method. Research lead by Mark Zylka, PhD has demonstrated some success using a similar method to treat Angelman syndrome (PWS’s sister syndrome) by utilizing CRISPR-Cas9 machinery to repair the missing UBE3A in the maternal chromosome 15 in mice that model Angelman syndrome finding embryonic and early postnatal treatment reduced physical and behavioral phenotypes that model core symptoms of the syndrome.

Conclusion
Ultimately, the GeneE method aims to give those with PWS an opportunity to live a healthier and more fruitful life through advances in gene therapy.

Author
Ryan Fue
rfue29@gmail.com