While skeletal and respiratory involvement is frequently present in the juvenile form, cardiac involvement is variable. There is no cardiac involvement in the adult form. This calculation is from estimated gene frequencies in normal individuals from various ethnic groups. As the weakness progresses, patients develop feeding difficulties and respiratory insufficiency. Enlargement of the left ventricle leads to outflow tract obstruction and ventricular failure.
Death results from cardiopulmonary failure.
Patients generally do not survive beyond the second or third decades of life. All patients have involvement of respiratory muscles and most die of respiratory failure. Several patients are reported to have died of basilar artery aneurysm. All were found to have abnormal storage within the lysosomes of arterial smooth muscle fibers. Age of onset does not predict age of death.