DNA-Analysis Technique Instrumental in Identifying Viral Infections and Drug Resistance in the Eye, Say UCSF Experts.

VANCOUVER, Canada--(BUSINESS WIRE)--July 12, 1996--A sensitive DNA-analysis technique called polymerase chain reaction (PCR) is extremely effective in diagnosing viral infections of the eye, including those occurring in patients with AIDS, and in identifying the cause of drug resistance in infected eyes, according to UCSF studies being presented at a special symposium as part of the 11th International Conference on AIDS today (July 12).

Scientists use PCR to detect and diagnose a variety of genetic and infectious diseases, from cystic fibrosis to cytomegalovirus (CMV) retinitis -- a chronic, destructive eye infection that can cause blindness in people with AIDS.

In PCR, a tiny amount of DNA is amplified a million fold, creating enough to analyze without the use of radioactive tracers. PCR makes it easier to look for defective genes that indicate genetic abnormalities or to look for the telltale DNA of infectious organisms that are difficult to isolate in the laboratory by traditional techniques.

UCSF eye researchers have been using PCR-based examinations to diagnose viral infections of the eye, such as CMV retinitis, in cases where diagnosis has been difficult to establish by other means. Michelle Knox, MD, an ophthalmology fellow at UCSF, presented study findings today of a new, rapid, sensitive and specific PCR-based test that can be used when the diagnosis of viral retinitis is uncertain. Knox and other researchers from the UCSF Proctor Foundation -- a research unit that studies blinding infectious and inflammatory diseases of the eye -- used PCR to detect CMV retinitis, varicella zoster virus and herpes simplex virus DNA among 21 vitreous samples from 20 AIDS patients with eye infections. The vitreous is the transparent substance that fills the part of the eyeball between the lens and the retina.

Knox reported that 10 samples tested positive for CMV retinitis DNA, all from AIDS patients whose clinical diagnosis became apparent over time. Three samples were positive for herpes simplex virus, all from patients with herpes encephalitis -- an inflammation of the brain caused by the herpes virus. Four samples tested positive for varicella zoster virus from patients subsequently diagnosed with the blinding disease.

Samples from four patients were negative for viral DNA -- one was eventually diagnosed as having ocular syphilis and one as toxoplasmosis (neither condition is caused by a virus), and two had obscure disease that resolved spontaneously without antivirals.

UCSF Proctor researchers developed the PCR techniques used for the study, which are the most sensitive and specific of any tests currently used for viral retinitis, according to UCSF ophthalmologist Todd P. Margolis, MD, PhD, associate director of the UCSF Proctor Foundation.

In a related study, Margolis and other UCSF researchers used PCR coupled with gene sequencing to identify the cause of resistance in 10 patients with CMV retinitis whose eyes were not responding to treatment with the drug ganciclovir.

"Many things can cause clinical resistance," Margolis says. "Until tested, we can't be sure if the resistance is due to poor patient compliance, inadequate drug dosage or the virus itself."

From the patients' vitreous samples, Margolis amplified fragments of the viral gene UL97, including the portion of the gene in which drug resistant mutations would likely be found. Vitreous samples from five patients with responsive CMV retinitis served as controls. The UCSF researchers found mutations at one of two separate points on the DNA sequence of seven patients. The mutations cause amino acid changes in the gene, indicating drug resistance.

In one patient, vitreous samples from both eyes were analyzed, revealing two different mutations at different points on the DNA sequence in each eye. These findings suggest that drug resistance may emerge independently in tissues of the eye, Margolis says.

Samples from patients whose disease responded to treatment did not have genetic mutations, according to the study.

"Clinically resistant CMV retinitis may be due to the emergence of resistant viral strains with mutations in the UL97 gene," Margolis says. "It is important to understand and identify the molecular basis for drug resistance so that we can apply more appropriate and cost-effective treatments for patients with CMV retinitis."

The satellite symposium on ocular HIV/AIDS research is a collaborative effort by the International AIDS Study Group of St. Paul's Hospital, Vancouver, the British Columbia Centre for Epidemiologic and International Ophthalmology, and the International Society for Geographical and Epidemiological Ophthalmology. It is produced in conjunction with the 11th International Conference on AIDS, this year held in Vancouver from July 7 through the 12th. -0-

Note to Editors: Media wishing to interview Drs. Knox or Margolis should call UCSF News Services at 415/476-2557. For more information about the satellite symposium, reporters should call 604/631-5169. For more information on the 11th International Conference on AIDS, call Gregory Hamara, conference media relations, at 604/668-3249.

CONTACT: UCSF

Rebecca Higbee, 415/476-2557