POSTER NO: 448

Development of Comprehensive Molecular Diagnostic Assays for Hunter Disease

¹Ying Qi, ²T. Brutzki, ²Peter N. Ray, ²Tracy L. Stockley
¹Dept. of Clinical Genetics, Qingdao Health Medical Center, 4 Renmin Road, Qingdao, 266033, P.R. China, ²Molecular Genetics Laboratory, Dept. of Pediatric Laboratory Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8

Hunter syndrome (mucopolysaccharidosis type II) is an X-linked recessive lysosomal storage disorder affecting approximately 1/130,000 live male births. The enzyme defect in Hunter syndrome is a deficiency of iduronate-2-sulphatase, which leads to lysosomal accumulation of the mucopolysaccharides - heparan sulfate and dermatan sulfate. The disorder has a wide spectrum of clinical phenotypes from mild to severe disease.

The causative gene for Hunter syndrome has been identified as the IDS gene on chromosome Xq28. The IDS gene contains nine exons and spans approximately 24 kb of genomic sequence. A pseudogene, IDS-2, also exists in the same region and contains similarity to exons 2, 3 and introns 2, 3 and 7 of the IDS gene with >90% homology. Many different mutations have been described for Hunter syndrome, and clinical variability has been related to different mutations in IDS gene. Mutations include deletions of exons of IDS and rearrangements of the IDS gene with the IDS2 gene (20%), and point mutations (80%). We have developed a comphrehensive molecular test for Hunter syndrome to confirm the clinical diagnosis of affected males and to detect female carriers. The molecular strategy for Hunter disease consists of three stages: (1) quantitative fluorescent PCR dosage analysis to detect exon deletions and duplications in affected males and female carriers (2) Southern blot analysis to detect IDS rearrangements and (3) scanning using denaturing high pressure liquid chromotography (DHPLC) and direct sequencing analysis to detect IDS point mutations. We have used this assay on several affected males and female relatives at risk of being carriers and to date we have identified 4 novel mutations in the IDS gene.