Your clients, Philip and Helen, have a disabled son, Alex, age 22.

A registered disability savings plan (RDSP) is a savings plan intended to help parents and others save for the long-term financial security of a person who is eligible for the disability tax credit (DTC). The DTC is a non-refundable tax credit that helps persons with disabilities or their supporting persons reduce the amount of income tax they may have to pay. To be eligible for the DTC, a person must have a severe and prolonged impairment in physical or mental functions, as defined by the Income Tax Act and as certified by a medical practitioner. Therefore, Alex must qualify for the DTC in order to be eligible for an RDSP. References: What is a registered disability savings plan (RDSP) - Canada.ca, Disability tax credit - Canada.ca