Method relating to myostatin pathway inhibition

A method for determining anabolic capacity of the skeletal muscle system of a subject, the method comprising:

• (a) determining a level of myostatin and/or follistatin in a systemic sample obtained from the subject;
• and/or
• (b) determining a level of myostatin and/or ActRII and/or follistatin in at least one muscle biopsy obtained from the subject;
• wherein if
• (i) the level of myostatin in the systemic sample is lower than a threshold and/or if the level of follistatin in the systemic sample is higher than a threshold;
• and/or
• (ii) the level of myostatin and/or ActRII receptor in the at least one muscle biopsy sample is lower than a threshold level and/or if the level of follistatin in the at least one muscle biopsy sample is higher than a threshold level,
• the anabolic capacity of the skeletal muscle system is compromised, indicating the existence of a muscle wasting process in the subject.

A method for determining whether a patient having or suspected of having spinal muscular atrophy (SMA) will respond to treatment, the method comprising:

• determining a level of myostatin and/or follistatin and/or GDF11 in a systemic sample obtained from the patient;
• wherein a level of GDF11 above a threshold is associated with SMA;
• and
• wherein if the level of myostatin is higher than a threshold and/or if the level of follistatin in the sample is lower than a threshold,
• the patient will respond to treatment.