William Blair analyst Raju Prasad believes the weakness in shares of PTC Therapeutics (PTCT) following Sarepta's (SRPT) micro-dystrophin gene therapy data is overblown. In a best-case scenario, the micro-dystrophin gene therapy could be approved in late 2021/early 2022 in the United States and potentially 2022/2023 in Europe, Prasad tells investors in a research note. As such, the analyst believes PTC management's projected five-year annual growth of 15% for Translarna due to increasing penetration in existing countries and potential label expansion remains likely. He still views Translarna and Emflaza revenues through 2022 plus cash on hand worth at least $35 per share, with $12 to $20 per share upside coming from risdiplam's potential in spinal muscular atrophy. Prasad keeps an Outperform rating on PTC Therapeutics.