About MPS I + MPS II

Hurler syndrome (also known as Mucopolysaccharidosis I, or MPS I) and Hunter syndrome (also known as Mucopolysaccharidosis II, or MPS II) are rare genetic diseases that result in the toxic buildup of complex sugars in the body called glycosaminoglycans, or GAGs. MPS I and MPS II can lead to serious medical problems including early death. Symptoms may not present at birth, but frequently appear in early childhood and may include delayed development, enlarged internal organs, heart conditions, stunted growth, skeletal abnormalities, and joint problems.

Underlying Genetic Cause of Disease

MPS I and MPS II are caused by mutations in a patient’s DNA, which lead to an inability to produce the enzyme alpha-L-iduronidase (IDUA) or iduronate-2-sulfatase (IDS), which normally breaks down GAGs. As a consequence, GAGs accumulate in the patient’s cells throughout the body and interfere with normal function. The severity of the disease varies, depending on the type of genetic mutation and rate of GAG buildup. MPS I and MPS II both encompass a broad spectrum of patients with mild-moderate or severe disease. Mild-moderate MPS I is also known as Scheie or Hurler-Scheie syndrome.

Symptoms of MPS I + MPS II

  • Abnormal bones, including shortened stature and spine problems
  • Intellectual disabilities
  • Heart disease
  • Enlarged liver and spleen
  • Joint stiffness
  • Vision or hearing loss
  • Depression
  • Chronic Pain
  • Shortened lifespan

Prevalence / Incidence

MPS I and MPS II are rare, genetic lysosomal storage disorders

All disease statistics are according to the National MPS Society


In 25,000 births will result in some form of MPS, in the U.S.


In 100,000 to 150,000 males are affected by MPS II (Hunter Syndrome)


MPS I patients in the U.S.

Three forms of MPS I, in order of increasing severity, include Scheie, Hurler-Scheie and Hurler syndromes.


Approximate number of MPS II patients in the U.S.

One in 100,000 male births in the U.S. will result in MPS II.

Sangamo’s Therapeutic Approach

Sangamo Therapeutics is developing genome editing treatments, SB-318 and SB-913, which are currently being tested for MPS I and MPS II. SB-318 and SB-913, are one-time experimental gene therapies designed to specifically insert a functional copy of the gene for the missing IDUA (MPS I) or IDS (MPS II) enzyme in the liver. The liver can then produce the missing enzyme potentially at high levels inside the body with the hope of improving or curing the disease, and possibly eliminating the need for lifelong ERT. SB-318 and 913 are being developed using Sangamo’s zinc finger nuclease (ZFN) genome editing technology. To learn more about how hour genomic therapies work, click the More Information button, below.

Resources for Patients and Families

Patient Stories


Born June 2014


Born December 2002


Born March 1983

Aiden + AJ

Aiden + AJ
Born September 2011 & March 2013
See all Stories