Among patients with retinal disease, molecular testing can confirm a clinical diagnosis of hereditary disorders, identify carrier status and confirm or rule out the presence of a familial mutation in those without symptoms, according to a report in the February issue of Archives of Ophthalmology, one of the JAMA/Archives journals.
The signs and symptoms of diseases of the retina, the light-sensitive membrane at the back of the eye that transmits images to the brain's optic nerve, overlap frequently, according to background information in the article. This can make a precise diagnosis difficult. Molecular testing, which screens for specific genetic mutations, is available for more than 950 genetic diseases, including many involving the eye.
Katy Downs, M.S., University of Michigan Kellogg Eye Center, Ann Arbor, and colleagues assessed the utility, scope and limitations of molecular testing in 350 tests performed at one laboratory: 266 diagnostic, nine predictive and 75 for carrier status. "Blood samples were submitted with a genetic test request form that included patient name, date of birth, sex, ethnic background, test(s) needed, indication for referral, family history depicted in pedigree format and the DNA testing consent form signed by the patient or the parent or guardian of a pediatric patient," the authors write. DNA was isolated from the blood samples and eight genes with mutations known to be involved with the retina were analyzed.
"The molecular basis of the disease was determined in 133 of 266 diagnostic tests; the disease-causing mutations were not identified in the remaining 133 diagnostic tests," the authors write. Of the nine predictive tests performed, five determined that the non-symptomatic individual did carry the same gene mutation as his or her affected relative, while four did not. Of the 75 females who underwent testing to confirm their carrier status, 47 were carriers of a mutation linked to retinal disease.
"The most common use of molecular diagnostic information of patients with retinal disease is to confirm a clinical diagnosis," the authors write. "The clinical presentation often was not straightforward, and the differential diagnosis could include several diseases. Molecular diagnostics does not replace the necessary expertise of the ophthalmologist; rather, it adds a new tool to the ophthalmologist's diagnostic arsenal."
"Molecular testing will likely become a standard of practice for the ophthalmologist," the authors conclude. "Because ocular molecular testing is still in its infancy, the ophthalmologist may encounter direct patient requests for testing and will need to determine when to order tests. Clinical molecular diagnostic laboratory personnel, including the laboratory director, the genetic counselor, and the clinical ophthalmic genetic specialist, can be of great value to the ophthalmologist by providing consultation before and after molecular genetic testing."
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