Insmed Incorporated (the study sponsor) is collecting information about classic AT to find out how the condition affects growth and development in children and whether there are better ways to monitor AT progression.

This non-promotional ‘observational’ and ‘exploratory biomarker’ study will include about 45 children with classic AT and 24 children without AT from the USA and the UK. Participants will not be asked to take any new medicines during the study. Enrolled participants will be in the study for up to 24 months and will visit the study site 5 times. The study sponsor will cover study-related travel expenses for all participants in applicable countries.