First-Ever WHIM Syndrome Drug Nears Landmark EU Approval

AMSTERDAM, NETHERLANDS – February 27, 2026 – Patients across Europe living with the ultra-rare and debilitating genetic disorder WHIM syndrome are a significant step closer to having an approved treatment for the first time. The European Medicines Agency's (EMA) Committee for Medicinal Products for Human Use (CHMP) has issued a positive opinion, recommending marketing authorisation for mavorixafor, a novel oral therapy.

The recommendation, welcomed by specialty pharmaceutical company Norgine B.V., paves the way for what could be the first medicine specifically designed to combat the underlying cause of WHIM syndrome. The European Commission (EC) is expected to make a final decision on the approval in the second quarter of 2026. If approved, the drug will be marketed under the brand name XOLREMDI®.

"We are pleased to see this important regulatory milestone for patients living with WHIM syndrome," said Janneke van der Kamp, Chief Executive Officer at Norgine. "At Norgine, we have built deep expertise in delivering rare and specialty medicines across Europe, Australia and New Zealand and the positive CHMP opinion for mavorixafor reflects the type of innovation our organisation is designed to bring to patients in need."

A Lifeline for an Ultra-Rare Disease

WHIM syndrome is a primary immunodeficiency so rare that fewer than 300 cases have been documented in medical literature, though estimates suggest the European population may be closer to 1,000 individuals. The condition's name is an acronym for its four classic, though not always present, manifestations: Warts, Hypogammaglobulinemia (low antibody levels), Infections, and Myelokathexis (the retention of white blood cells in the bone marrow).

The disorder stems from a genetic mutation that causes the CXCR4 receptor to become overactive. This dysfunction effectively traps mature white blood cells—specifically neutrophils and lymphocytes—in the bone marrow, preventing them from entering the bloodstream to fight off pathogens. The resulting chronic neutropenia (low neutrophil count) and lymphopenia (low lymphocyte count) leave patients highly susceptible to frequent, severe, and sometimes life-threatening bacterial and viral infections.

Until now, patients have relied on a regimen of supportive care. This includes continuous or prophylactic antibiotics, immunoglobulin replacement therapy to boost antibody levels, and injections of granulocyte colony-stimulating factor (G-CSF) to try and force more neutrophils out of the bone marrow. However, these treatments only manage symptoms and do not address the root genetic cause, leaving a significant unmet medical need and a heavy burden on patients' quality of life.

The Science Behind Mavorixafor

Mavorixafor represents a paradigm shift in treating WHIM syndrome. As a selective CXCR4 antagonist, the once-daily oral capsule works by blocking the faulty receptor. This action breaks the "trap," allowing the mature neutrophils and lymphocytes to be released from the bone marrow into circulation, thereby restoring a crucial component of the body's immune defense system.

The CHMP's positive opinion is anchored by robust data from the pivotal 4WHIM trial, a global, 52-week, randomized, placebo-controlled Phase 3 study. Though the trial involved just 31 patients—a reflection of the disease's rarity—its results were compelling.

The study met its primary endpoint, showing that patients treated with mavorixafor spent a significantly longer time with their absolute neutrophil counts above a key threshold compared to those on placebo (an average of 15.0 hours versus 2.8 hours over a 24-hour period). A key secondary endpoint for lymphocyte counts was also met.

More importantly, these biological improvements translated into tangible clinical benefits. Patients taking mavorixafor experienced a 40% reduction in the total score of infections (a measure combining number and severity) and a nearly 60% reduction in the annualized rate of infections compared to the placebo group. The treatment was generally well-tolerated, with the most common side effects including low platelet counts, rash, and nosebleeds. The drug is already approved in the United States under the name XOLREMDI®, where it was authorized by the FDA in April 2024.

Navigating a Niche Regulatory Path

The journey of mavorixafor to potential approval highlights a specialized regulatory mechanism crucial for rare disease therapies. The CHMP's recommendation is for a "marketing authorisation under exceptional circumstances." This pathway is specifically designed for situations where, due to the rarity of a condition, it is not possible for an applicant to provide a comprehensive set of efficacy and safety data under normal conditions of use.

For diseases like WHIM syndrome, enrolling hundreds or thousands of patients in a clinical trial is impossible. The "exceptional circumstances" pathway acknowledges this reality, allowing regulators to grant approval based on the available evidence, provided the benefit-risk balance is positive for the intended patient population who currently have no other options.

This type of authorization is not a free pass; it comes with specific obligations. The company will be required to implement a robust risk management plan and conduct post-authorization studies to gather additional long-term safety and efficacy data from patients in a real-world setting. This framework allows urgently needed medicines to reach patients while ensuring that knowledge about the drug continues to grow after it enters the market.

A Strategic Play in the Rare Disease Market

The potential European launch of mavorixafor is the result of a strategic partnership between its developer, the U.S.-based X4 Pharmaceuticals, and Norgine. Under an agreement established in January 2025, Norgine acquired the exclusive rights to commercialize the therapy in Europe, Australia, and New Zealand.

This collaboration leverages the strengths of both companies: X4's innovation in drug discovery and Norgine's extensive commercial infrastructure and deep expertise in navigating the complex market access landscapes across Europe. As part of the deal, X4 is eligible to receive up to €226 million in milestone payments on top of double-digit royalties on net sales, signaling strong commercial expectations for the drug.

For Norgine, a mid-sized European company with a strong focus on specialty and rare disease products, mavorixafor is a cornerstone asset that reinforces its strategic mission. Successfully bringing the first targeted therapy for WHIM syndrome to market would not only provide a vital new option for a neglected patient community but also solidify Norgine's position as a key player in the highly competitive and scientifically-driven orphan drug market. The approval would underscore the value of a regulatory system flexible enough to address the unique challenges posed by the rarest of diseases.