Study of ASP2957 in male patients with X-linked Myotubular Myopathy who need ventilators

X-linked myotubular myopathy (XLMTM) is a rare and serious condition present at birth where the muscles do not work properly. There are currently no therapies for XLMTM.

The protein myotubularin is needed for muscle development and movement. A gene called MTM1 tells the body to make myotubularin. XLMTM is caused by changes, or mutations, in the MTM1 gene. Changes in the MTM1 gene causes low or no levels of myotubularin to be made, so the muscles do not work properly.

Gene therapy is a way of getting a healthy copy of a gene into the body. This allows the body’s cells to make a normal protein that may reduce disease symptoms. ASP2957 is an experimental gene therapy treatment that gets a healthy MTM1 gene into the body to help improve muscle development and function in young children with the disease.

In this study, ASP2957 will be given to boys for the first time. This is known as a “first in human” study. Boys 3 years or younger with XLMTM can take part.

The main aims of this study are to check the safety of ASP2957, how well the boys tolerate it, and to find the most suitable dose. The study will also check if ASP2957 reduces how long the boys spend on a ventilator.

This study has 2 parts. In Part 1, the boys will receive a single injection given slowly through a tube into a vein (infusion) of ASP2957. In Part 2, a few more boys will be given the dose of ASP2957 worked out from Part 1.

In both parts of the study, the boys will be followed-up for health checks for up to 1 year after their infusion of ASP2957.