X-Linked RP Sometimes Misdiagnosed as Autosomal Dominant RP

February 13, 2013
A team led by Dr. Stephen Daiger, a researcher from the University of Texas Health Science Center in Houston, used genetic testing to determine that 8.5 percent of people thought to have autosomal dominant retinitis pigmentosa (adRP) actually have X-linked RP (XLRP). The investigators tested individuals from a group of 258 families initially diagnosed with adRP. Results of the Foundation-funded study were recently published in the journal Investigative Ophthalmology and Visual Science.

Dr. Daiger says these results have “substantive implications” in determining which family members may be at risk for inheriting RP and which emerging treatments, such as a gene-specific therapy, may be beneficial.

“Dr. Daiger’s findings underscore the importance of genetic testing and counseling for people with retinal diseases,” says Dr. Stephen Rose, the Foundation’s chief research officer. “RP is a complex and diverse group of conditions. While a genetic diagnosis can be challenging to obtain, it can paint a clearer picture of inheritance risks and future treatment opportunities for affected families.”

In autosomal dominant diseases, one parent usually has the condition (e.g., RP) and has a 50 percent chance of passing it along to a child. In these cases, the disease is often seen in several generations of a family. Also, males and females are equally likely to be affected; a person’s gender plays no role in determining the risk of getting the condition. To date, defects in 23 genes are known to cause adRP.

The science community’s understanding of XLRP, which has a more complex inheritance pattern, has changed recently. It has been known for many years that males with an XLRP mutation are always affected, often severely. Experts also believed that females who carried an X-linked mutation were not affected by RP but had a 50 percent chance of passing the disease along to their sons.

But recent studies have revealed that female carriers can, in fact, be affected, sometimes as severely as males. However, XLRP is not as genetically diverse as adRP; three genes — RPGR, RP2 and OFD1 — cause a vast majority of cases.

Information on genetics and genetic testing
is available, for free, on the Foundation’s website.

In addition to conducting genetic research, Dr. Daiger maintains RetNet, a Foundation-funded, online catalogue of all known retinal disease genes. It is an invaluable, no-cost reference resource for the international research community and anyone interested in retinal disease genetics.