Lymphocyte Gene Therapy for Mild Hunter Syndrome 
2.2.3 Molecular Genetics 
Recent cloning and sequencing of the human IDS coding region (6) has made possible the 
characterization of specific mutations causing Hunter syndrome. Cumulated results of work in 
this laboratory and several others have determined that many patients (14 of 62 studied) have 
major gene deletions or rearrangements as detected by Southern analysis (7-9) or by reverse 
transcription (RT) linked to polymerase chain reaction (PCR) (10, 11). Such major gene defects are 
found in patients with severe disease having neurologic involvement. 
However, most affected individuals have single-base substitutions. To rapidly identify all 
such mutations, we recently developed an automated method to sequence the entire IDS coding 
region from small blood specimens (12). To date, work in this laboratory (13) and others (10, 14- 
19) has identified approximately 30 mutations thus providing an index of genotype-phenotype 
correlations differentiating "severe" and "mild" forms. Patients with severe Hunter syndrome 
have frame-shift mutations, non-sense mutations, or amino acid substitution at a critical position. 
Patients with mild Hunter syndrome typically have missense mutations which cause a relatively 
conservative amino acid substitution at a less critical position or which cause splicing errors. 
Mutation analysis by automated sequencing has proven to be an excellent diagnostic method and 
will be a major criterion in determining eligibility of patients for this study. 
2.3 Current Therapy 
Existing therapy for Hunter syndrome is limited to symptomatic treatment and palliative 
procedures (such as herniorrhaphy, carpal tunnel repair, tracheotomy, etc.). No conventional 
therapy is curative or significantly alters the natural course of the disease. Even experimental 
bone marrow transplantation (BMT) is now generally viewed as unacceptable for most patients 
with Hunter syndrome (described below). 
2.3.1 Bone Marrow Transplantation 
Allogeneic BMT has been accomplished for several of the MPS diseases as a means of 
providing a continuous, systemic source of enzyme. In 1981, successful engraftment of normal 
bone marrow into children with Hurler syndrome (MPS I, alpha-L-iduronidase deficiency) was 
first reported. (20, 21) Continuing clinical trials have substantiated improvement in several 
biochemical and pathophysiologic correlates collectively described as "metabolic correction". (22) 
Subsequent animal studies of marrow transplantation were conducted in a feline model of 
Maroteaux-Lamy syndrome (MPS VI, N-acetylgalactosamine 4-sulfatase deficiency) (23), a canine 
model of Hurler-Scheie syndrome (23-26), a murine model of Sly syndrome (MPS VII, 6- 
glucuronidase deficiency) (27), and a number of other lysosomal storage diseases. From these 
studies it has become apparent that many biochemical and physiologic improvements occur 
following engraftment. 
The morbidity and the limitations of treatment continue to be defined as engrafted children 
mature (28). Thirty-eight patients with MPS have undergone bone marrow transplantation at the 
University of Minnesota using a closely-matched donor (29). The outcome of this group with 
respect to survival is tabulated below (Table 1). 
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