Genetic disease markers could be distinguished using fluorescent probes, according to Italian scientists.

A large degree of genetic variance, known as polymorphism, exists between individuals. These genetic differences mostly involve only one nucleotide, but they can be linked to genetic disease.

Detecting variations in the gene sequence could reveal a patient's susceptibility to autoimmune diseases, such as diabetes

Alessandra Andreoni at the University of Insubria, Como, Italy, and colleagues used fluorescent nucleotides to identify single nucleotide polymorphisms in a group of genes associated with the development of type 1 diabetes. The nucleotides had a fluorescent label at one end and a quencher at the other and contained either a complementary sequence of the gene region or polymorphic variations.

Polymorphic probes don't bind as well as the complementary probe to the gene sequence, explains Andreoni. The polymorphic probes bend, bringing the quencher closer to the fluorescent label and so decreasing the fluorescence decay time.

'More efficient quenching at reduced label-quencher distance reveals more errors in the probe-to-target sequence matching,' says Andreoni. This enabled the team to determine the degree of base mismatch quantitatively, an improvement over the 'yes or no' binding information provided by other methods. They also were able to identify the specific base change for each target.

'We could reliably type [identify] the targets by using a single probe and working with a few millilitres of low-concentration targets,' states Andreoni. 'We are thus confident that our technique can be used to diagnose non-amplified genome samples. As sequence variants, though not necessarily directly pathogenic, are often linked to the occurrence of diseases, the possibility to perform wide range screening of the relevant genes would give a powerful tool in disease prediction.'

Michael Spencelayh

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