Affected patients have both visceral (the internal organs of the body, for example, the lungs, liver and spleen) and neurological (brain) involvement. However, the neurological involvement is much less severe than in type 2.
Most patients have significant visceral disease which tends to respond well to treatment such as enzyme replacement therapy (ERT). For example the liver and spleen may return to normal size. However, not all aspects of the visceral disease respond well, and this results in varying degrees of chronic ill-health.
Neurological involvement is present almost from birth and in most cases, remains very mild and stable for the majority of patients, with minimal progression, throughout life. However, for some patients it can be quite severe and progressive.
Even in the mild group there are significant implications for day-to-day living, education, and independence.
The combination of chronic visceral and neurological involvement means that patients need careful monitoring. Equally important, as they grow to become young adults and become more independent, they need to become empowered to be able to access information themselves