Delayed Mental Development

Severely affected individuals experience a slowing of mental development by 1–3 years of age, followed by a progressive regression in skills (i.e., the child’s mental development and skills gradually become less advanced over time) for the rest of their lives. There is great variation in the severity of the condition, however; some may say only a few words, while others learn to walk well and to read a little. They can enjoy nursery rhymes and simple puzzles.

Some parents emphasize that it is important to help severely affected babies learn as much as they can before the disorder progresses. Even when the child starts to lose the skills he or she has learned, there may still be some surprising abilities left. Children will continue to understand and to find enjoyment in life even if they lose the ability to speak.

Individuals on the Hurler side of the spectrum commonly have other medical problems that can hamper their learning and performance, including chronic ear infections, poor vision, poor hearing, communicating hydrocephalus (in older layperson’s terms called “water on the brain”), and sleep apnea (temporarily stopping breathing while sleeping). Comprehensive medical assessments should be performed for individuals whose development is significantly affected.

Individuals who are less severely affected (historically called Hurler-Scheie) can have normal cognitive function, but some will have moderate learning difficulties. They can also suffer from the effects of medical problems that hinder their learning and communication.

People with the Scheie disease usually have normal cognitive function, although there have been some reports of cognitive issues in this group. It is important to remember that MPS I is a spectrum. Some patients have milder physical problems and learning disabilities, while others have more severe physical problems and normal cognitive function.