title: A study of the relationship between clinical phenotypes and plasma iduronate-2-sulfatase enzyme activities in Hunter syndrome patients.
abstract: OBJECTIVE
  Mucopolysaccharidosis type II (MPS II or Hunter syndrome) is a rare lysosomal storage disorder caused by iduronate-2-sulfatase (IDS) deficiency. MPS II causes a wide phenotypic spectrum of symptoms ranging from mild to severe. IDS activity, which is measured in leukocyte pellets or fibroblasts, was reported to be related to clinical phenotype by Sukegawa-Hayasaka et al. Measurement of residual plasma IDS activity using a fluorometric assay is simpler than conventional measurements using skin fibroblasts or peripheral blood mononuclear cells. This is the first study to describe the relationship between plasma IDS activity and clinical phenotype of MPS II.
  
  
  METHODS
  We hypothesized that residual plasma IDS activity is related to clinical phenotype. We classified 43 Hunter syndrome patients as having attenuated or severe disease types based on clinical characteristics, especially intellectual and cognitive status. There were 27 patients with the severe type and 16 with the attenuated type. Plasma IDS activity was measured by a fluorometric enzyme assay using 4-methylumbelliferyl-α-iduronate 2-sulphate.
  
  
  RESULTS
  Plasma IDS activity in patients with the severe type was significantly lower than that in patients with the attenuated type (P=0.006). The optimal cut-off value of plasma IDS activity for distinguishing the severe type from the attenuated type was 0.63 nmol·4 hr(-1)·mL(-1). This value had 88.2% sensitivity, 65.4% specificity, and an area under receiver-operator characteristics (ROC) curve of 0.768 (ROC curve analysis; P=0.003).
  
  
  CONCLUSIONS
  These results show that the mild phenotype may be related to residual lysosomal enzyme activity.
authors.affiliation: Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Ok Jeong
authors.initials: OJ
authors.lastname: Lee
authors.forename: Su-Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Young Bae
authors.initials: YB
authors.lastname: Sohn
authors.forename: Hyung-Doo
authors.initials: HD
authors.lastname: Park
authors.forename: Soo-Youn
authors.initials: SY
authors.lastname: Lee
authors.forename: Chi-Hwa
authors.initials: CH
authors.lastname: Kim
authors.forename: Ah-Ra
authors.initials: AR
authors.lastname: Ko
authors.forename: Yeon-Joo
authors.initials: YJ
authors.lastname: Yook
authors.forename: Su-Jin
authors.initials: SJ
authors.lastname: Lee
authors.forename: Sung Won
authors.initials: SW
authors.lastname: Park
authors.forename: Se-Hwa
authors.initials: SH
authors.lastname: Kim
authors.forename: Sung-Yoon
authors.initials: SY
authors.lastname: Cho
authors.forename: Eun-Kyung
authors.initials: EK
authors.lastname: Kwon
authors.forename: Sun Ju
authors.initials: SJ
authors.lastname: Han
authors.forename: Dong-Kyu
authors.initials: DK
authors.lastname: Jin