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Regenxbio said on Monday the U.S. FDA has placed its experimental gene therapy for a \u200brare inherited disorder on clinical hold after spinal scans found \u200cabnormalities in five study participants, sending its shares down more than 24% in premarket trading.<\/strong><\/p>\n The therapy, RGX-121, was being developed as a one-time treatment for Hunter Syndrome, also \u200bknown as MPS II, which can cause progressive damage to \u200bthe brain and other organs and tissues.<\/p>\n The spinal scans identified \u2060a small lump or fluid-filled mass in the patients who received the \u200btreatment, RGX-121, about three to six years ago, the biotech said.<\/p>\n The setback \u200badds to Regenxbio\u2019s regulatory troubles after the U.S. Food and Drug Administration declined to approve RGX-121 earlier this year over concerns about the trial design and supporting evidence.<\/p>\n RGX-121 was \u200balso subject to the health regulator\u2019s previous clinical hold on the company\u2019s two \u200bgene therapy programs.<\/p>\n The therapy uses a harmless virus known as AAV9 vector to deliver \u200cthe \u2060gene needed to produce the missing enzyme in patients with Hunter syndrome.<\/p>\n Current treatment options include Takeda Pharmaceutical\u2019s\u00a0Elaprase, a weekly infusion that treats the physical effects of Hunter syndrome, and Denali Therapeutics\u2019\u00a0Avlayah, approved in March, to \u200btreat neurological symptoms in \u200bcertain children.<\/p>\n Regenxbio \u2060said the five patients remained asymptomatic and were clinically stable or showed improvements in cognitive and behavioral assessments. Trial \u200binvestigators deemed the findings to be non-serious and radiologists \u200bbelieved \u2060they were likely benign.<\/p>\n The company said it does not expect to resubmit its application for the treatment\u2019s approval in the near term.<\/p>\n It, along with partner \u2060NS Pharma, \u200bwill review additional imaging and longer-term follow-up \u200bdata and await the FDA\u2019s full clinical hold letter before deciding the next steps for \u200bRGX-121.<\/p>\n<\/div>\n