Mucopolysaccharidosis I Disease Testing

What is Mucopolysaccharidosis I (MPS-I)?

Mucopolysaccharidosis (MPS) is a group of inherited and progressive genetic disorders characterized by a deficiency of the lysosomal enzymes responsible for degradation of glycosaminoglycans.1 The subsequent accumulation of intra-lysosomal accumulation products (chondroitin sulfate, heparan sulfate, dermatan sulfate and keratan sulfate) results in multi‑organ dysfunction involving various tissues.1 This accounts for the different phenotypes seen in the Mucopolysaccharidosis disorders.1

Mucopolysaccharidosis Ι (MPS-Ι) results from deficient activity of the lysosomal enzyme α‑L‑iduronidase (IDUA), which leads to an accumulation of the glycosaminoglycans (GAGs) dermatan sulfate and heparan sulfate.1,2 Mucopolysaccharidosis I is inherited in an autosomal recessive manner and clinical findings may include developmental delay, musculoskeletal dysfunction, frequent upper respiratory tract infections, and cardiac involvement.2 Symptoms of Mucopolysaccharidosis I vary in severity but are usually described as severe MPS-I (previously known as Hurler syndrome) and attenuated Mucopolysaccharidosis I (previously known as Hurler-Scheie and Scheie syndromes), with varying disease progression, organ involvement, and age of disease onset.2  

What is the Incidence of Mucopolysaccharidosis?

The overall incidence of mucopolysaccharidosis is estimated at approximately 1/25,000 births.1 Severe MPS-I is seen in all populations at a frequency of approximately 1:100,000 and in the attenuated form at approximately 1:500,000.2

The Roadmap2Rare Diagnostic Program Eligibility

This rare disease testing program is designed for HCPs with eligible patients when there is clinical suspicion of MPS-I. The program includes single disorder testing for MPS-I (α-L-iduronidase enzyme assay with reflex to IDUA sequencing if deficient).

*Note: this diagnostic program is not appropriate for carrier testing.

What is the Mucopolysaccharidosis I Test?

For single disorder testing, the algorithm is as follows:

  1. α-L-iduronidase enzyme is assayed
  2. If enzyme levels are found to be deficient, IDUA sequencing is performed

In the event that sequencing or enzyme assay activity testing has been performed previously, individual tests can be ordered.


  1. Nagpal R, et al. Indian J Ophthalmol. 2022;70:2249–61.
  2. Clarke LA. Mucopolysaccharidosis Type I. 2002 Oct 31 [Updated 2021 Feb 25]. In: Adam MP, et al. editors. GeneReviews® _[Internet]. Seattle (WA): University of Washington, Seattle; 1993-2023. Available from:

The Roadmap2Rare Diagnostic Program is not intended to and should not interfere in any way with a clinician’s or patient’s independent judgment and freedom of choice in the testing and treatment options for these diseases. Clinicians and patients should always consider the full range of testing and treatment options and select those most appropriate for the individual patient. The identifying information of patients and clinicians is not shared with Sanofi Canada.