Pompe's disease is a very rare condition which causes weakness of the respiratory muscles and may therefore cause symptoms of breathlessness or even respiratory failure, requiring the use of a ventilator at night. Recently a treatment for this condition has become available as well as a simple diagnostic test. However, we believe it is possible that there are patients with this condition who are presently undiagnosed attending respiratory clinics.

We would like to complete an observational study of patients with respiratory muscle weakness of an unknown cause, who are attending respiratory clinics at two London centres, to determine whether patients attending these services have undiagnosed Pompe's disease.

Participation in the study will involve taking measurements of respiratory muscle strength, lower limb strength and collecting blood samples to test for enzymes which relate to Pompe's disease. These measures will be completed during a routine clinic visit. Participation will also involve the study coordinator accessing medical notes to gain information about disease history.

The study aims to collect information about the number of patients attending respiratory clinics with undiagnosed Pompe's disease and the characteristics of these patients so that other specialist services could use these criteria to identify patients who may benefit from investigations and treatment. If any participants are diagnosed with Pompe's disease and could benefit from treatment medical staff would refer them for treatment at local UK centres.

Inclusion Criteria:

Patients presenting to home mechanical ventilation or other respiratory clinics:

who are over 18 years old with unexplained respiratory muscle weakness with breathlessness and/or type II respiratory failure which may be treated by a ventilator which is: unexplained by a known pulmonary disease, radiological abnormality or distortion of body hiatus (e.g scoliosis or massive obesity defined as BMI > 50 kg/m2), associated with a restrictive ventilatory defect or associated with unexplained muscle weakness.

Exclusion Criteria:

respiratory muscle weakness confirmed to be due to another cause known to have Pompe's disease at time of referral

Adults aged over 18 presenting to respiratory clinics with respiratory muscle weakness of an unknown cause.