Core Viewpoint - Pharming Group announced that the FDA issued a Complete Response Letter (CRL) for its supplemental New Drug Application (sNDA) for Joenja® (leniolisib) as a treatment for children aged 4 to 11 years with activated phosphoinositide 3-kinase delta syndrome (APDS) [1][5] Regulatory Update - The FDA raised concerns about potential underexposure in lower weight pediatric patients and requested additional pharmacokinetic data to reassess proposed doses [2] - An issue was identified with one of the analytical methods used for production batch testing, prompting the FDA to request further data and clarification [2] - Pharming plans to address the issues outlined in the CRL and intends to request a Type A meeting with the FDA to discuss next steps for resubmission [3] Clinical Data - The sNDA submission was based on positive results from a Phase III study showing improvements in lymphadenopathy and naïve B cells over 12 weeks, indicating a correction of the immune defect in children [4] - Safety data from 8 months of treatment indicated that all treatment-emergent adverse events were mild to moderate, with no serious drug-related adverse events reported [4] Market Context - Currently, there are no approved treatments for children with APDS under the age of 12 globally, highlighting the significance of Joenja's potential impact [5] - Joenja received FDA approval for treating APDS in patients aged 12 years and older in March 2023, which remains unaffected by the recent regulatory action [3][5] Disease Overview - APDS is a rare primary immunodeficiency characterized by severe recurrent infections and immune dysregulation, affecting approximately 1 to 2 people per million worldwide [6] - The condition is caused by variants in the PIK3CD or PIK3R1 genes, leading to hyperactivity of the PI3Kδ pathway, which impairs immune cell function [6] Product Information - Leniolisib is an oral PI3Kδ inhibitor approved in several countries as the first targeted treatment for APDS in patients aged 12 years and older [7] - The drug is currently under regulatory review in multiple regions and is being evaluated in clinical trials for other primary immunodeficiencies [8]