And the phenotype changes with age: all are progressive disorders! (MPS I as example)

This is a girl aged 12 with a severe Hurler phenotype. If you have an intermediate Hurler-Scheie phenotype which is not that severe in young age, you will end up with quite severe clinical disease later on, and with the Scheie phenotype, which was the attenuated phenotype, if left untreated patients become wheelchair-bound and severely incapacitated.