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The genetics of muscle mass

More than 10 % of individuals over the age of 65 suffer from age-related loss of muscle mass (MM). Finding new genetic determinants of muscle development will help to find treatment for muscle-wasting conditions.
The genetics of muscle mass
A loss of MM and strength with ageing or due to disease leads to compromised quality of life. MM is determined by the number and size of the mature cells of the muscle tissue (the muscle fibres). There are substantial differences among individuals in the number and size of muscle fibres in individual muscles.

Half of the variations in MM are hereditary, indicating that individuals can have greater or smaller MM because they inherited certain variants of the relevant genes. The identity of such genes is of particular interest because they could offer targets for the development of treatments for muscle-wasting conditions.

Studies in mammals show that common mechanisms are involved in the regulation of muscle properties in different species. The EU-funded 'Genetic mechanisms of muscle fibre variation' (GENETMUSCLEFIBREVAR) project aimed to find the primary genetic determinants of MM. In particular, the study focused on the soleus muscle, which in mice encompasses the same types of fibres that are found in human muscles.

At first, researchers analysed the role of genes in determining the properties of fibres in the mouse soleus muscle. The number, size and proportion of the different types of fibres were examined in 11 strains of laboratory mice. As the number of fibres remains largely unchanged after birth, the role of genes is particularly important. It was found that the number of fibres can differ by more than two-fold in solei of different strains. These findings revealed that certain MM can be achieved in different ways: through the number, size and proportion of different fibre types. Thus, suitable models for searching out genes involved in genetic determination of the muscle were established.

In the next phase of the project researchers conducted a search for specific genes affecting the properties of muscle fibres using models they developed. Ann association analysis allowed identification of the link between the specific regions of the genome and the trait of interest in the population. The analysis identified a number of genome regions that contributed to the difference in fibre size and proportion of different types of fibres between the two strains. Genomic regions that harbour more than one gene have been examined and further studies would be required in order to identify the causative genes.

Identification of these specific genes will open new targets for pharmacological agents to combat muscle loss. One advantage of developments in this area will also favour livestock breeders, who would be able to develop breeds with favourable meat quality and better yield.

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