MPS I Spectrum of Disease
MPS I patients are commonly categorized into one of three clinical groups depending upon their cognitive functioning; Hurler, Hurler-Scheie, and Scheie. These three phenotypes can be further classified into two subgroups, Severe and Attenuated. The Hurler patients make up the Severe group, while Hurler-Scheie and Scheie patients belong to the Attenuated group. Patients with pronounced mental delays with loss of acquired skills are generally classified as Hurler or Severe MPS I patients. Those with no to mild learning disabilities are commonly classified as Hurler-Scheie and those with no cognitive impairments are classified as Scheie patients.
Hurler patients make up the majority of MPS I patients and are usually diagnosed the earliest due to other severe clinical presentations. The attenuated patients (Hurler-Scheie and Scheie patients) show greater variability in their age of diagnosis, rate of disease progression, and organ system impairment. Nevertheless, all phenotypes across the MPS I spectrum are progressive and debilitating.
The top 5 presenting symptoms by MPS I patients varies depending on the severity of the disease. According to MPS I Registry (Beck et al, 2014), corneal clouding and hernias are common symptoms reported by all MPS I patients, however, the age of onset varies amongst the groups. Hurler patients commonly present with coarse facial features, hepatomegaly, and kyphosis while Attenuated patients present with cardiac valve abnormalities, joint contractures, and carpal tunnel. The median age of symptom onset is within the first year of life for Hurler patients while Hurler-Scheie and Scheie patients don’t present until childhood.
Signs and Symptoms of Attenuated MPS I
References: 1. Muenzer J. Pediatrics. 2009;123(1):19-29. 2. Neufeld EF, Muenzer J. The Metabolic and Molecular Basis of Inherited Disease. 2001:3421-3452. 3. Beck M. Genet Med. 2014;16(10):759-65.