Pharma giant Pfizer will pay up to $800 million to acquire Swiss biotech Therachon in a deal that will expand its rare disease portfolio with a potential first-in-class therapy for achondroplasia, a genetic disorder that results in short-limb dwarfism.

Achondroplasia is the most common type of short-limbed dwarfism and occurs in one in 15,000 to 40,000 newborns worldwide, or about 250,000 people. It is caused by mutations in the FGFR3 gene that controls making a protein involved in the development and maintenance of bone and brain tissue, leading to dwarfism of the arms and legs, limited range of motion at the elbows, large head size, small fingers, and more serious spinal problems. Treatment usually involves medication with growth hormone.

Therachon’s TA-46 is an investigational, soluble recombinant human fibroblast growth factor receptor 3 (FGFR3) decoy, a mechanism of action that is believed to normalize the overactive FGFR3 signaling pathways that underlie bone development abnormalities associated with achondroplasia. Therachon is developing TA-46 as a weekly subcutaneous injection for children and adolescents living with the condition. TA-46 has completed phase 1 studies and has received Orphan Drug designation from the European Medicines Agency and the U.S. Food and Drug Administration.

Under the terms of their agreement, Pfizer will pay Therachon’s shareholders $340 million upfront and up to another $470 million in milestones tied to the development and commercialization of TA-46.

Therachon will spin out its remaining rare disease asset, apraglutide, into a new company. Apraglutide is a GLP-2 analog in mid-stage development for short bowel syndrome. Pfizer Ventures, the venture capital arm of Pfizer, currently holds a minority stake and will continue to hold an equity stake in the new company.

“Pfizer’s existing research programs for pediatric growth disorders provide a complementary setting for this potential breakthrough therapy,” said Seng Cheng, senior vice president and chief scientific officer of Pfizer’s Rare Disease Research Unit. Pfizer’s existing research portfolio in rare diseases includes a late-stage candidate to treat pediatric and adult growth hormone deficiency.

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