New DNA test to diagnose disease linked to childhood blindness

22 August 2014

A new study, published in Ophthalmology, the journal of the American Academy of Ophthalmology, has indicated that using advanced DNA testing for congenital cataracts could help quickly and accurately diagnose a number of rare diseases.

The British researchers used a single test that then enabled the doctors to better tailor care to the individual child, which reduced the time and money spent on diagnosis and enabling earlier treatment and genetic counseling. The findings could help the 20,000 to 40,000 children who are born with congenital cataracts each year. The condition clouds the lens of the eye and often means surgery is needed to prevent the child going blind. It can also be triggered by a maternal infection or be inherited as an isolated abnormality. 

However, congenital cataracts can also be a symptom of more than 1,000 rare diseases, which makes mutations in the 115 genes associated with congenital cataracts useful as diagnostic markers for the illnesses.

The researchers found, for 75 per cent of the 36 cases analysed, the DNA test was able to pinpoint the exact cause of congenital cataracts. In one instance, the test led to the diagnosis of Warburg Micro syndrome for a patient, which is an extremely rare disease marked by a small head and the development of severe epilepsy, among other medical issues. 

A clear diagnosis allows doctors to tailor genetic counseling and appropriate care to be delivered quicker than previously possible without the test. Diagnosing rare diseases is often a costly and lengthy process, as it involves numerous clinical assessments and taking a detailed family history, but even this can be inconclusive.

DNA testing, which involves analysing each gene individually, can take years, but using new DNA sequencing technology, called targeted next-generation sequencing, diagnosis has been rapidly quickened. 

The researchers at the University of Manchester decreased the time it takes to get a diagnosis to just a few weeks by testing all 115 known congenital cataracts genes at one time.

Professor Graeme Black, of genetics and ophthalmology at the University of Manchester and strategic director of the Manchester Centre for Genomic Medicine, said: "There are many diseases that involve congenital cataracts but finding the exact reason was always difficult", adding that diagnosing these rare diseases is "always a bit of a shot in the dark".

During their research with the Manchester Royal Eye Hospital, the team found that previously undescribed mutations could be 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 has been made available to patients in the UK on the NHS from December 2013 and all infants and children who have congenital cataracts can be tested as well as prospective parents with a history of the condition.

Results can take around two months, and although only available in the UK, the congenital cataract DNA test can be requested by registered medical facilities through international referral.

Posted by Philip Briggs​

 

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