Mucopolysaccharidoses (MPS)

NINDS describes seven distinct types, each caused by a different missing enzyme. They are MPS I (Hurler, Hurler-Scheie and Scheie syndromes), MPS II (Hunter), MPS III (Sanfilippo), MPS IV (Morquio), MPS VI (Maroteaux-Lamy), MPS VII (Sly) and the extremely rare MPS IX. Each type ranges from severe to milder forms. This guide covers MPS I, II, VI and VII, the types NMDP lists as treatable with a donor transplant.

Severe MPS I (Hurler syndrome) is the clearest case: GeneReviews calls transplant the standard of care for children with it. European guidelines published in 2026 also list MPS II as a standard reason for transplant, and MPS VI as an option when enzyme therapy fails or is not possible. EBMT’s 2025 recommendations rate MPS II to VII as a case-by-case option, and a 2026 U.S. review found no clear agreement for MPS II. The 2026 European guidelines say transplant is generally not recommended for MPS IIIA (Sanfilippo type A), because the disease keeps progressing despite it.

Donor cells can slow the decline in thinking, but they cannot undo damage already done. EBMT’s 2025 recommendations say the best results come with transplant before age 2 from a donor who does not carry the condition. A 2011 European consensus says children diagnosed before age 2½ with signs of the severe form should be referred for transplant. It adds that children with major developmental delay (a DQ under 70) are less likely to benefit. Newborn screening can help find children early.

No. NINDS says there is currently no cure, and care aims to treat symptoms and improve quality of life. A donor transplant can change the course of severe MPS I, but EBMT notes it does not completely remove long-term problems. GeneReviews adds that bones, joints, eyes and the heart respond less. Enzyme replacement helps many body problems but does not cure the disease.

Standard enzyme replacement, given by vein, is used for MPS I, II, IVA, VI and VII. NINDS says it can reduce symptoms outside the brain and pain but does not help nervous system symptoms, because the enzyme does not cross the blood-brain barrier. In March 2026, the U.S. gave accelerated approval to tividenofusp alfa (Avlayah), the first medicine approved in the U.S. for the brain effects of MPS II. It is for children weighing at least 5 kg, started before advanced brain impairment, and a confirmatory trial is under way.

In the U.S., MPS I was added to the federal Recommended Uniform Screening Panel in February 2016 and MPS II in August 2022. Each state decides what its program screens for. As of December 2025, 45 of 54 U.S. programs screened for MPS I. A positive screen is followed by enzyme, GAG and genetic tests, because many flagged babies have a harmless variant called pseudodeficiency rather than MPS.

Most types are autosomal recessive: a child has MPS when they inherit a changed gene from each parent, and each pregnancy of two carrier parents has a 1 in 4 chance. MPS II is the exception. It is X-linked, so a mother who carries the gene change can pass it to a son, and it almost always affects boys. Genetic counseling can help families understand testing for relatives and future pregnancies.