Lysosomal Disorders

All diseases supported by the Canadian MPS Society are classified as Lysosomal Storage Diseases (LSDs). These can be described simply as a genetic (or inborn) error of metabolism. They are caused by the absence of an enzyme that is needed to break down a substance in the body. Without the enzyme there is a buildup – or “storage” – of these substances. Over time, individuals affected by LSDs experience a loss of function, or deterioration, in one or several crucial areas of the body. This may result in mental and physical disability as well as drastically shortened lifespan.

Disease Name (Alternate Name)

Mucopolysaccharide Storage Diseases:

  • MPS I (Hurler Syndrome; Scheie Syndrome; Hurler-Scheie Syndrome)
  • MPS II (Hunter Syndrome)
  • MPS IIIA, IIIB, IIIC, IIID (Sanfilippo Syndrome)
  • MPS IVA & IVB (Morquio Syndrome)
  • MPS VI (Maroteaux-Lamy Syndrome)
  • MPS VII (Sly Syndrome)
  • MPS IX (Hyaluronidase Deficiency)

Complex Carbohydrate Storage Disorders:


In the mucolipidoses (ML) class of LSDs, all of the mucopolysaccharide enzymes are present, but in most cases the enzymes continually leak out of the cell. As a result, the mucopolysaccharides are not completely broken down. The lysosomal enzymes in the ML disorders lack a phosphate group which is necessary for directing the enzymes into the lysosomes. Therefore, the mucopolysaccharide and lipid materials accumulate in the cells and tissues.

The ML disorders have symptoms including coarse facial features, stiff joints, stunted growth, heart murmurs, and mental retardation ranging from mild to severe. Some of those affected with ML experience clouding of the cornea, enlarged liver and spleen, and ear infections. Like MPS, ML diseases are progressive and degenerative.

  • ML I (Sialidosis)
  • ML II (I Cell Disease)
  • ML III (Pseudo-Hurler Polydystrophy)
  • ML IV (Berman Syndrome)


  • Mannosidosis A & B
  • Fucosidosis
  • Aspartylglycosaminuria (AGU)
  • Multiple Sulfatase Deficiency (MSD)
  • Schindler Disease
  • Sialuria
  • Sialic Acid Storage
  • Galactosialidosis
  • Cobalamin F Mutation
  • GSD II (Pompe Disease)

How common are these diseases?

These diseases are very rare and sometimes misdiagnosed, so it is difficult to give accurate figures on frequency. The current estimate is that 2 or 3 individuals per one million births are diagnosed with ML II and ML III.

How is the disease inherited?

We all have all the genes inherited from our parents which control whether we are tall, short, fair, etc. Some genes we inherit are “recessive,” that is to say we carry the gene but it does not have an effect on our development. I-Cell and Pseudo-Hurler syndrome are caused by a recessive gene. If an adult carrying the abnormal gene marries another carrier there will be a one in four chance with every pregnancy that the child will inherit the defective gene from each parent and will be affected with the disease. There is a two in three chance that unaffected brothers and sisters of an individual with ML will be carriers. They can be reassured, however, that as the disease is so rare, the chance of marrying another carrier is very slight provided they do not marry a cousin or other close family member.

Is there a cure?

At present there is treatment for symptoms as they arise but no cure for the underlying condition. Various experimental methods have been used to try to replace the missing enzyme, but none so far has been of any significant long term benefit.
All families of affected children should seek further information from their doctor or from a Genetic Counselor.

 Complex Lipid Storage Disorders


  • GM 1 gangliosidosis (Landing’s Disease)
  • GM 2 gangliosidosis (Tay-Sach’s & Sandhoff’s Diseases)
  • Trihexosylceramidosis (Fabry’s Disease)
  • Glucosylceramidosis (Gaucher Disease)
  • Sphingomylceramidosis (Niemann-Pick Diseases A, B & C)
  • Sulfatidosis (Metachromatic Leukodystrophy – MLD)
  • Galactosylceramidosis (Krabbe’s Disease)
  • Lipogranulomatosis (Fabrer’s Disease)
  • Wolman’s Disease
  • Fucosidosis
  • Shindler Disease
  • Multiple Sulfatase Deficiency
  • Sphingolipid Activator Deficiency
  • Cholesterol Ester Storage Disease
  • GMZ Activator Deficiency
  • Cystinosis