ABOVE: The therapy targets a gene in the liver.

The first patients to have received a medium dose of a gene therapy based on in vivo gene editing have lower levels of sugar in their urine—a hopeful sign that the intervention for Hunter syndrome is working. However, clinicians did not observe an increase in levels of the enzyme they hoped to replace, Sangamo Therapeutics, which developed the treatment, reported today (September 5).

“I cannot absolutely say it’s a treatment effect,” study leader Joseph Muenzer of the University of North Carolina, Chapel Hill, tells the Associated Press. But he adds that the data are “really encouraging.” 

Hunter syndrome is a rare disease in which an enzyme deficiency leads to a buildup of complex polysaccharides. Those with the condition often die young.

See “First In Vivo Genome Editing to Be Tested in New Clinical Trial”...

The first person to have received the treatment got it back in November. The infusion includes a normally functioning gene for the dysfunctional enzyme and zinc finger nucleases to cut the genome and insert the gene. The treatment is targeted to the liver.

See “Man Receives First In Vivo Gene-Editing Therapy

In this latest trial, two people received a medium dose of the gene-editing reagents and two people, including the first patient, got a low dose. After 16 weeks, those who received the low dose experienced no change in their urine sugar levels. The medium-dose patients, on the other hand, saw three urine biomarkers—glycosaminoglycans, dermatan sulfate, and heparan sulfate—decline by 51 percent, 32 percent, and 61 percent, respectively.

Levels of iduronate-2-sulfatase, the enzyme targeted by the gene therapy, remained undetectable at the beginning and end of the trial’s assessments. Endpoints News reports that the result triggered a 22-percent drop in Sangamo’s stock this morning. The company says the lack of detectable enzyme doesn’t mean the gene therapy isn’t working.

“If longer-term data from this study continue to be positive, therapeutic genome editing has the potential to bring tremendous medical progress for [Hunter] and other monogenic diseases,” Edward Conner, chief medical officer of Sangamo, says in a press release sent to The Scientist.

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