OHSU

OHSU Primate Center Scientists Develop Gene Therapy Method to Prevent Some Inherited Diseases

08/21/09  Portland, OR

Breakthrough could help break the chain of several maternally-based diseases passed from generation to generation; Results in the birth of twin monkeys named “Mito” and “Tracker,” the world’s first animals derived by a fertility method called spindle transfer

Researchers at Oregon Health & Science University’s Oregon National Primate Research Center (ONPRC) believe they have developed one of the first forms of genetic therapy – a therapy aimed at preventing serious diseases in unborn children. Specifically, the therapy would combat inherited diseases passed on from mothers to their children through mutated DNA in cell mitochondria. The research is published in the Aug. 26 advance online edition of the journal Nature and will appear in a print edition of the journal at a later date.  

“We believe this discovery in nonhuman primates can rapidly be translated into human therapies aimed at preventing inherited disorders passed from mothers to their children through the mitochondrial DNA, such as certain forms of cancer, diabetes, infertility, myopathies and neurodegenerative diseases,” explained Shoukhrat Mitalipov, Ph.D., an associate scientist in the Division of Reproductive Sciences at ONPRC, the Oregon Stem Cell Center and the departments of Obstetrics and Gynecology and Molecular & Medical Genetics of Oregon Health & Science University (OHSU). “Currently there are 150 known diseases caused by mutations of the mitochondrial DNA, and approximately 1 out of every 200 children is born with mitochondrial mutations.”

Mitochondria are structures that are found in all cells that provide energy for cell growth and metabolism, which is why they are often called the cell’s “power plant.” The structures produce energy to power each individual cell. Mitochondria also carry their own genetic material.

When an egg cell is fertilized by a sperm cell during reproduction, the embryo almost exclusively inherits the maternal mitochondria present in the egg. This means that any disease-causing genetic mutations that a mother carries in her mitochondrial DNA can be passed on to her offspring. The method developed by OHSU researchers transfers the mother’s chromosomes to a donated egg that has had its chromosomes removed, but which has healthy mitochondria, thereby preventing the disease from being passed on to one’s offspring.

Here is how the OHSU researchers’ method works: Scientists collected groups of unfertilized eggs from two female rhesus macaque monkeys (monkeys A and B). They then removed the chromosomes, which contain the genes found in the cell nucleus, from the eggs of monkey B, and then transplanted the nuclear genes from the eggs of monkey A into the eggs of monkey B. Then the eggs from monkey B, which now contained their own mitochondria but monkey A’s nuclear genes, were fertilized. The fertilized eggs developed into embryos that were implanted in surrogate monkeys.

Diagram of proposed mitochondrial gene replacement therapy
Diagram of proposed mitochondrial gene replacement therapy
The nuclear DNA from a patient’s egg carrying mitochondrial DNA mutations is removed and transplanted into an egg donated by a healthy donor which has also had its nuclear DNA removed. The reconstructed egg cell (oocyte) is then fertilized with the partner's sperm and an embryo is transferred to a patient. The baby will be free of risk from maternal mitochondrial mutations, but yet the biological child of the parents. - Click to Enlarge

The initial implantation of two embryos resulted in the birth of healthy twin monkeys, nicknamed “Mito” and “Tracker” (in reference to the procedure used for imaging of mitochondria). These monkeys are the world’s first animals derived by spindle transfer.

Follow-up testing showed that there was little to no trace of cross-animal mitochondrial transfer using this procedure. This demonstrates that the researchers were successful in isolating nuclear genetic material from mitochondrial genetic material during the transfer process.

“In theory, this research has demonstrated that it is possible to use this therapy in mothers carrying mitochondrial DNA diseases so that we can prevent those diseases from being passed on to their offspring,” added Mitalipov. “We believe that with the proper governmental approvals, our work can rapidly be translated into clinical trials for humans, and, eventually, approved therapies.”

“This breakthrough is an excellent example of how OHSU’s research findings can often be rapidly translated into health therapies that benefit residents of our state and the country as a whole,” said Dr. Joe Robertson, M.D., M.B.A., president of OHSU.

The research was funded by the Oregon National Primate Research Center, the Oregon Stem Cell Center; and the National Center for Research Resources and the National Institute of Child Health and Human Development, both components of the National Institutes of Health.         
   
About ONPRC
The ONPRC is a registered research institution, inspected regularly by the United States Department of Agriculture. It operates in compliance with the Animal Welfare Act and has an assurance of regulatory compliance on file with the National Institutes of Health. The ONPRC also participates in the voluntary accreditation program overseen by the Association for Assessment and Accreditation of Laboratory Animal Care International (AAALAC).

About OHSU
Oregon Health & Science University is the state's only health and research university and Oregon's only academic health center. OHSU is Portland's largest employer and the fourth largest in Oregon (excluding government). OHSU's size contributes to its ability to provide many services and community support activities not found anywhere else in the state. It serves patients from every corner of the state, and is a conduit for learning for more than 3,400 students and trainees. OHSU is the source of more than 200 community outreach programs that bring health and education services to every county in the state.