Researchers Identify New Gene Causing Blindness

From left: Stephan Zuchner, M.D., Ph.D., assoc. prof. of genetics; Julia Dallman

From left: Stephan Zuchner, M.D., Ph.D., assoc. prof. of genetics; Julia Dallman, Ph.D., asst. prof. of biology; Margaret A. Pericak-Vance, Ph.D.; director, John P. Hussman Institute for Human Genomics; Byron Lam, M.D., prof. of ophthalmology; and Rong Wen, Ph.D., assoc. prof of ophthalmology.

— Miami — Researchers led by geneticists at the University of Miami Miller School of Medicine have identified a new gene that causes retinitis pigmentosa, a form of blindness, ending one South Florida family’s nearly 20-year search for what caused three of their four children to lose their sight.

The Lidsky children, who are now in their 30s, began to lose their sight in their teens. Their parents, Betti and Carlos, had the family’s DNA tested for more than 50 retinitis pigmentosa (RP) genes. No one found the link until they began working with UM researchers in late 2009. By the summer of 2010, researchers had found the cause of their retinitis pigmentosa using exome sequencing and confirmed it with zebrafish studies.

‘For 18 years, we have been searching for the genetic cause of this disease and UM researchers have found it,’ Mrs. Lidsky said. ’We’ve wanted this for some time. These researchers are truly our heroes. They are doing life-changing work that will benefit not only our family but many other people. We are truly grateful for all their hard work.’

The result of the work, a paper titled ‘Whole-exome sequencing links a variant in DHDDS to retinitis pigmentosa,’ was published online Thursday, February 3, in the American Journal of Human Genetics . To identify the gene responsible for retinitis pigmentosa in the Lidsky family, researchers used a new technology known as whole exome sequencing, which thoroughly investigates the coding portions of an individual’s genetic material. The RP gene identified in this family codes for an enzyme known as dehydrodolichol diphosphate synthase or DHDDS, which is thought to play a role in how a light-sensing protein named rhodopsin works.

The research was led by Margaret A. Pericak-Vance, Ph.D., associate dean for human genomic programs, the Dr. John T. Macdonald Foundation Professor of Human Genomics, and director of the John P. Hussman Institute for Human Genomics, along with Stephan Züchner, M.D., Ph.D., first author of the paper and director of the Center for Human Molecular Genomics at the Hussman Institute, and Byron Lam, M.D., professor of ophthalmology at Bascom Palmer Eye Institute.

‘This was a powerful demonstration of what we can do with new genetic technologies,’ Dr. Zuchner said. Important evidence to support this gene as the cause of RP comes from research with zebrafish, led by collaborator Julia Dallman, Ph.D., in the Department of Biology at UM. When researchers in her lab blocked the enzyme, the fish became blind.

Researchers from five areas of the University of Miami - the John P. Hussman Institute for Human Genomics , the Dr. John T. Macdonald Foundation Department of Human Genetics, Bascom Palmer Eye Institute , the Department of Biochemistry and Molecular Biology, and the Department of Biology - worked together to make this exciting discovery. Researchers from the Department of Psychiatry at Mount Sinai School of Medicine and the Center for Human Genetics Research at Vanderbilt University School of Medicine also contributed to the work.

‘This research brings hope to families that have rare genetic diseases whose causes had formerly eluded researchers using traditional methods,’ said Dr. Pericak-Vance, senior author on the paper. ‘We now can bring hope to families who formerly thought their situation was hopeless.’

‘This is another example of how genomics research is critically important to our work here at the Miller School of Medicine,’ said Pascal J. Goldschmidt, M.D, Senior Vice President for Medical Affairs and Dean of the Miller School. ‘It makes a difference in people’s lives. In addition, it exemplifies the team approach to research we take here at UM.’

Retinitis pigmentosa refers to a large group of diseases that cause degeneration of the retina of the eye. The retina is located at the back of the eye and its role is to capture light that enters the eye, which is translated into images by the brain. In RP there is damage to the cells in the retina that capture light, known as cones and rods. Over time, these cells slowly stop working and vision deteriorates. One of the first signs of RP is night-blindness, or the slow adaptation to dim light. As RP progresses, people develop tunnel vision, which can eventually lead to a complete loss of vision. RP is diagnosed in approximately 1 in 3,000 to 4,500 people and is known to be caused by changes, or mutations, in many genes.

Dr. Lam has treated the Lidsky siblings with retinitis pigmentosa - Isaac Lidsky, Daria Zawadzki, and Ilana McGuinn - for several years. He called the RP finding an ‘exciting discovery.’

‘Our success in identifying this novel DHDDS gene associated with retinitis pigmentosa demonstrates the power of new genetic methodology to find the cause of disease in small families,’ said Dr. Lam. ‘Finding the genetic causes of retinal degeneration is important because it will lead to a better understanding of retinal biology overall.’

‘The current findings will encourage further studies designed to examine the role of proteins in the formation and renewal of light-sensitive photoreceptor cells in the retina and how retinitis pigmentosa occurs,’ said Eduardo Alfonso, M.D., chair of Bascom Palmer Eye Institute. ‘The ultimate implications are better patient care and the possibility of developing new therapies.’

While there is no cure for RP at this time, HIHG and Bascom Palmer researchers said the discovery holds promise to develop new avenues for therapy.

‘We need to come at this from different angles,’ explained Jeffery M. Vance, M.D., Ph.D., professor and chair of the Dr. John T. Macdonald Foundation Department of Human Genetics, professor of neurology and director of the Center for Genomic Medicine at the Hussman Institute for Human Genomics. Dr. Vance is also a co-author on the paper. ‘UM researchers are creating models using both zebrafish and skin cells from patients to develop possible treatments, but they will take some time to test.’

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