Efgartigimod Application Submitted for Seronegative gMG, EC Approves High-Dose Nusinersen, Copper Histidinate Gains First Approval for Menkes Disease

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Welcome to this special edition of Neurology News Network. I'm Marco Meglio.

According to a company update, the FDA has accepted Argenx’s supplemental biologics license application (sBLA) for efgartigimod (Vyvgart), positioning it as potentially the first treatment for adults with acetylcholine receptor antibody (AChR-Ab) seronegative generalized myasthenia gravis (gMG). The agency has granted a Prescription Drug User Fee Act target action date of May 10, 2026, for the decision. Seronegative gMG, which affects approximately 15% of the total gMG population, has typically been treated using the same overall clinical playbook as antibody-positive gMG; however, there are no FDA-approved treatments specific to this subgroup. Efgartigimod, an engineered Fc fragment of human immunoglobulin G1 designed to bind tightly to the neonatal Fc receptor, was initially approved for seropositive gMG in 2021 and had its indication expanded in 2024 to include the treatment of those with chronic inflammatory demyelinating polyneuropathy.

Biogen recently announced that the European Commission (EC) has granted marketing authorization for a high-dose, potentially more efficacious regimen of nusinersen (Spinraza) for patients with 5q spinal muscular atrophy (SMA). The newly approved high-dose regimen includes a more rapid loading phase consisting of two 50 mg loading doses administered 14 days apart, followed by 28-mg maintenance doses every 4 months thereafter. Notably, patients transitioning from the previously approved 12-mg regimen will receive a single 50-mg dose in place of their next scheduled 12-mg dose, followed by 28-mg maintenance dosing every four months.

Months after the FDA issued a complete response letter (CRL) to the new drug application (NDA) for Sentynl Therapeutics’ copper histidinate, the agency has approved the agent as the first treatment for pediatric patients with Menkes disease, a rare genetic neurodegenerative disorder. Marketed as Zycubo, the therapy is a subcutaneous copper replacement treatment that delivers copper in a form designed to bypass impaired intestinal absorption and support systemic utilization of the mineral. The company resubmitted a revised NDA for copper histidinate on November 14, 2025, following receipt of a CRL from the FDA on September 30, 2025. In the CRL, the agency cited observations related to current good manufacturing practice compliance at the manufacturing site. According to Sentynl, no additional approvability concerns were identified, and the FDA did not note deficiencies in the efficacy or safety data, which showed improved overall survival among patients with Menkes disease who received early treatment.

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