KIDS: DNA TEST FOR DISEASES LINKED TO BLINDNESS
Researchers in the
United Kingdom have demonstrated that advanced DNA testing for congenital
cataracts can quickly and accurately diagnose a number of rare diseases marked
by childhood blindness, according to a study published online in Ophthalmology, the journal of the American Academy of
Ophthalmology. Using a single test, doctors were able to tailor care
specifically to a child's condition based on their mutations, reducing the time
and money spent on diagnosis and enabling earlier treatment and genetic
counseling
Each year, between
20,000 and 40,000 children worldwide are born with congenital cataracts, a
disease that clouds the lens of the eye and often requires surgery and
treatment to prevent blindness.[i] The disease can arise following a maternal
infection or be inherited as an isolated abnormality. Congenital cataracts can
also appear as a symptom of more than 100 rare diseases, making mutations in
the 115 genes associated with congenital cataracts useful as diagnostic markers
for the illnesses.
Diagnosing these rare
diseases previously proved a lengthy, costly and inconclusive process involving
numerous clinical assessments and taking a detailed family history. DNA
testing, one gene at a time, would have taken years to complete. Employing new
DNA sequencing technology, called targeted next-generation sequencing,
researchers at the University of Manchester sped up diagnosis to a matter of
weeks by testing for mutations in all 115 known congenital cataracts genes at
one time.
In 75 percent of the
36 cases tested, the DNA test determined the exact genetic cause of congenital
cataracts. In one case, the DNA test helped diagnose a patient with Warburg
Micro syndrome, an extremely rare disease that is marked by an abnormally small
head and the development of severe epilepsy, among other medical issues. Having
a clear diagnosis allowed for genetic counseling and appropriate care to be
delivered quicker than previously possible without the test.
"There are many
diseases that involve congenital cataracts but finding the exact reason was
always difficult," said Graeme Black, DPhil., professor of genetics and
ophthalmology at the University of Manchester and strategic director of the
Manchester Centre for Genomic Medicine. "Even with a family history,
diagnosing these rare diseases was always a bit of a shot in the dark."
In the course of their
work, done in collaboration with Manchester Royal Eye Hospital, researchers
also found previously undescribed mutations linked to cataract formation.
"There is hope that our work may one day provide more insight into the
development and treatment of age-related cataracts, a leading cause of
blindness worldwide," said Rachel Gillespie, MSc, lead author of the study
who designed and developed the test.
The test was made
available to U.K. patients through the country's National Health Service in
December 2013. Infants and children who have congenital cataracts can be tested
as well as prospective parents with a history of the condition who wish to
evaluate the risk to their child. Results generally take about two months.
While only available in the U.K., the congenital cataract DNA test can be
requested by registered medical facilities through international referral.
As with all genetic
testing, the American Academy of Ophthalmology encourages clinicians and
patients to consider the benefits as well as the risks. Ophthalmologists who
order genetic tests either should provide genetic counseling to their patients
themselves, if qualified to do so, or should ensure that counseling is provided
by a trained individual, such as a board-certified medical geneticist or
genetic counselor. For more information, please see the Academy's
recommendations on genetic testing for inherited eye diseases.
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