Avatar Mouse Model Sheds Insights into Customized Medicine in a Rare Disease

The mouse model developed paves way for customized therapy in Allan-Herndon-Dudley syndrome, a rare disease.

Researchers used CRISPR to integrate into the mice a mutation of the MCT8 protein responsible for transporting thyroid hormones to the interior of the cell.

This study, published in Neurobiology of Disease, describes the first avatar model for the disease, in other words, the first animal with the same genetic alteration as various patients.

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Rare or orphan diseases are least understood of all chronic diseases. They are more common than projected and kill more people than cancer and HIV together.

‘Patients with mutations in the MCT8 protein suffer from Allan-Herndon-Dudley syndrome, a rare disease which takes the form of serious neurological alterations, in which each patient may reveal a different mutation of MCT8.’

"The development of avatar models faithfully reproducing the patients' alterations with this same mutation is the first step towards targeted therapy. It specifically lays the foundations to allow us to study the possible "genetic repair" of this mutation in an animal model, and to evaluate whether this serves to avoid or revert the serious neurological alterations which exist in such patients", according to Carmen Grijota, researcher at the Cellular Biology Department of the UCM and IIBM, explaining the importance of the study.

Same Neurological and Motor Alterations in Avatars and Humans

This study used mice carrying the “P321L” mutation. Tests were conducted to study the behaviour, levels of anxiety and motor coordination capacity of the mice. The animals' brains were then extracted and specific stains applied to review and study different types of neuron.

"Lastly, an in-depth computerized analysis was conducted to understand how the mutation could be affecting the structure of the MCT8 carrier, and hence its function of transporting thyroid hormones," adds Víctor Valcárcel, IIBM researcher and co-author of the paper.

The alterations seen in the mice included cerebral hypothyroidism (lack of thyroid hormones in the brain), hyperthyroidism (excessive thyroid hormones in the other tissues), alterations in the distribution of the neurons in the cerebral cortex, and a reduction in GABAergic neurons. Alterations were likewise noted in motor coordination, as well as anxious behaviour in the mutant mice. All these findings reflect the alterations characteristic of patients suffering from the disease.

Test Your Knowledge on Rare Diseases
Rare or orphan diseases are the least understood of all the categories of chronic diseases. Rare diseases are more common than projected and globally they take away more lives than cancer and HIV combined.

Globally around 350 million people are estimated to live with a rare disease. Currently, there are 7000 rare diseases with newer ones being discovered each year. 80% of rare diseases have a genetic origin. Rare diseases may be single-gene disorders or multiple- gene disorders. Almost 50% of those affected are children and 30% of these children will not live beyond the age of 5. It takes nearly 7 years to diagnose a rare disease. 95% of rare diseases do not have a cure.

According to the scientists, the next steps to be taken in their research would involve the administration of drugs that mimic the activity of thyroid hormones, but do not require MCT8 to enter the cells, because they use other different carriers. “The idea is to ascertain whether these drugs can reach the brain of the mutant mouse and improve all these alterations”, explains IIBM researcher, Marina Guillén.

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Aside from these two institutions, the study also involves the Functional Genomics Institute of Lyon in France, and the University of Bristol in the UK.

Source-Eurekalert

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