- Have a medical condition, serious inter-current illness, or other extenuating circumstance that may interfere with study compliance including all prescribed evaluations and follow-up activities, except the 6MWT. (Note: All patients may not be capable of performing the 6MWT due to age and/or maturity level. Exemption from performing the 6MWT must be obtained in writing by the investigator from the sponsor's medical monitor prior to enrollment).