1. ¹Department of Pediatrics, Saint Louis University, Pediatric Research Institute, St Louis, MO, USA
2. ²Department of Pediatrics, Gifu University School of Medicine, Gifu, Japan
3. ³Department of Pediatrics, Shimane University, Shimane, Japan
4. ⁴Centre d'Etude des Maladies Métaboliques, Hôpital Debrousse, Lyon France
5. ⁵Institut de Bioquimica Clinica, Barcelona, Spain
6. ⁶Willink Biochemical Genetics Unit, Royal Manchester Children's Hospital, Great Britain, UK
7. ⁷Department of Biochemistry and Medical Biotechnologies, University of Naples, Federico II, Italy
8. ⁸Institut fur Humangenetik, Universitatsklinikum Hamburg-Eppendorf, Hamburg, Germany
9. ⁹Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St Louis, MO, USA

Correspondence: S Tomatsu, Department of Pediatrics, Saint Louis University Pediatric Research Institute, 3662 Park Ave., St Louis, MO 63110-2586, USA. Tel: +1 314 577 5623, ext. 6213; Fax: +1 314 577 5398; E-mail: tomatsus@slu.edu

Received 14 September 2005; Revised 14 February 2006; Accepted 15 February 2006; Published online 12 April 2006.

Abstract

Hunter syndrome, an X-linked disorder, results from deficiency of iduronate-2-sulfatase (IDS). Around 40% of independent point mutations at IDS were found at CpG sites as transitional events. The 15 CpG sites in the coding sequences of exons 1 and 2, which are normally hypomethylated, account for very few of transitional mutations. By contrast, the CpG sites in the coding sequences of exon 3, though also normally hypomethylated, account for much higher fraction of transitional mutations. To better understand relationship between methylation status and CpG transitional mutations in this region, the methylation patterns of 11 Hunter patients with transitional mutations at CpG sites were investigated using bisulfite genomic sequencing. The patient cohort mutation spectrum is composed of one mutation in exon 1 (one patient) and three different mutations in exon 3 (10 patients). We confirmed that in normal males, cytosines at the CpG sites from the promoter region to a portion of intron 3 were hypomethylated. However, specific CpG sites in this area were more highly methylated in patients. The patients with p.R8X (exon 1), p.P86L (exon 3), and p.R88H (exon 3) mutations had a hypermethylated condition in exon 2 to intron 3 but retained hypomethylation in exon 1. The same trend was found in four patients with p.A85T (exon 3), although the degree of hypermethylation was less. These findings suggest methylation patterns in the beginning of IDS genomic region are polymorphic in humans and that hypermethylation in this region in some individuals predisposes them to CpG mutations resulting in Hunter syndrome.