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Clinical exome sequencing in the diagnosis of intellectual disability

Pictogramme horloge Grégory EGEA Pictogramme horloge November 2016

Intellectual disability is a major challenge in public healthcare. This disorder affects between 1 and 2% of the population and is of genetic origin in half of all cases.

Genetic disorders are a range of clinically heterogeneous diseases, all caused by one or more variations at exon level.

In over 50% of cases, it is not possible to establish a diagnosis using conventional clinical and biological approaches.

We now know that the human genome contains about 20,000 genes (200,000 exons), these coding sequences representing around 1% of the total genome. These exons account for about 85% of the mutations causing diseases of genetic origin.

At Eurofins Biomnis, the multidisciplinary team responsible for exome sequencing in a routine clinical context studies approximately 99% of a patient’s medically relevant genes in a single analysis, using the NGS technique. At the end of the analytical and bioinformatics process, an average of 20,000 variations are considered in the biological interpretation and, in relation to intellectual disability, the genetic abnormality responsible can be identified in 23-35% of cases, compared with the 10-15% of cases identified with the conventional approach.

The localized mutations, insertions, deletions, inversions, and some rearrangements can potentially be demonstrated with the medical exome study.

Identification of the mutation responsible is a considerable breakthrough in the management of intellectual disability. Not only does it help reduce the number of undiagnosed patients, but it also offers physicians a new, reliable and high precision tool for making treatment decisions, in order to adapt the specific support and monitoring of the patient, or even to propose specific and personalized treatment in some cases.

For many families, the sequencing of the exome ends the diagnostic guesswork, and makes it possible to offer a prenatal diagnosis during genetic consulting.

In addition to intelectual disability, Eurofins Biomnis offers medical exome analyses in France and internationally for other pathologies: autism, epilepsy, neurodevelopmental disorders, cardiomyopathies, metabolic diseases, etc.

So that we can perform this analysis, you must send us two 5ml EDTA tubes at ambient temperature within a maximum delivery time of 4 days.

The medical interpretation of this analysis is based on the current state of knowledge, but reinterpretation may be required if requested by the prescribing physician in accordance with changes in the patient data.

If a mutation which may explain the indication is detected, this is confirmed by a complementary technique, Sanger sequencing. In this situation, the availability of the results will be delayed.

Given the complexity of the interpretation, we recommend a trio analysis, i.e. the simultaneous analysis of the index case with that of each parent. Also, in some cases, other members of the family may be involved to obtain a clear result.

The cost of the clinical exome is available on request.
The TAT is  6 weeks from sample receipt for a negative result, however,  it may be extended if specific confirmations are required.

In the near future, the rate of diagnosis of pathologies of genetic origin will be further improved with the development of sequencing of the entire genome …


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