Lysosomal storage diseases (LSDs) are inherited metabolic diseases in which there is a deficiency in the lysosomal enzymes needed to break down carbohydrates or fats.

Lysosomes function as the primary digestive unit within cells. People with these LSDs lack or have malfunctioning lysosomal enzymes, which leads to an abnormal accumulation of certain complex carbohydrates or fats within various tissues, including the skeleton, joints, brain, spinal cord, heart, spleen, and/or liver. Cells within these organs become dysfunctional, leading to a wide variety of symptoms including enlargement of spleen or liver, bone deformities, respiratory and cardiac problems, and neurological problems.

There are more than 50 types of LSDs, with mucopolysaccharidoses (MPS) being the most common type. The combined incidence of LSDs is estimated to be approximately 1:5,000 live births worldwide. 1 LSDs largely affect children.


1 Platt F.M., Boland, B., and C. van der Spoel, A. (2012). Lysosomal storage disorders: The cellular impact of lysosomal dysfunction. The Journal of Cell Biology, vol. 199 no. 5 723-734.

Currently approved enzyme-replacement therapies do not penetrate the blood-brain barrier and therefore do not address the severe and progressive neurological complications of many lysosomal storage diseases.