FDA Accepts Wearable Sensor-Derived Foot Drop Metrics Under ISTAND as Longitudinal Outcome Measures in Rare Neurological Condition

[9/22/2026] The Food and Drug Administration's Innovative Science and Technology Approaches for New Drugs (ISTAND) program has accepted a letter of intent (LOI) for a wearable sensor-derived digital outcome measure intended to quantify foot drop severity and its impact on gait in adult patients with Charcot-Marie-Tooth disease type 1A (CMT1A), a progressive, degenerative disease. This LOI represents the first submission to be accepted into the ISTAND program for a digital health technology (DHT) for a rare neurological condition.

"Acceptance of this submission into the ISTAND program reflects our commitment to advancing objective, patient-relevant measurement approaches in rare disease drug development and our support for innovative methods that could strengthen the evidence base for emerging CMT1A therapies,” said Vanitha Sekar, PhD, Director of Biomedical Informatics, Regulatory Tool Innovation and Biomarker Development in the Center for Drug Evaluation and Research (CDER)’s Office of New Drugs (OND).

The accepted LOI is for a wearable sensor-based measurement tool that captures quantitative metrics of foot drop (the inability to lift the front of the foot caused by nerve damage, leading to muscle weakness) severity during the six-minute walk test performed at scheduled clinic visits. The tool is intended to be used in clinical trials to measure foot drop progression as an efficacy outcome. The tool uses movement sensors on the ankles and feet to capture foot drop-specific parameters, including ankle range of motion, foot drop angle, and mid-swing foot angle. This LOI represents both a DHT and a novel approach to outcome measurement in neuromuscular drug development, both important areas of focus for CDER.

CMT1A is the most common inherited peripheral neuropathy, with a prevalence of approximately 1 in 5,000, and currently has no FDA-approved therapies. Wearable sensor-derived metrics of foot drop captured during a timed walking test are expected to provide objective, continuous, high-resolution measurements that are more sensitive to treatment-related change than existing clinical scales.

"The Charcot-Marie-Tooth community consistently says that foot drop has been one of the most functionally significant symptoms affecting daily independence and quality of life, yet current clinical endpoints do not capture this concept precisely," said Laura Jawidzik, MD, Director of the Division of Neurology 2 in CDER’s OND.

This LOI acceptance is the first step of the three-stage qualification process in the Drug Development Tool (DDT) Qualification Programs.

Launched in 2020, the ISTAND program aims to support the development of novel DDTs for use in regulatory applications for new medical products, particularly tools that do not readily fit into established qualification pathways, such as those for biomarkers and clinical outcome assessments. The program opens opportunities for DDTs that address specific drug development needs and demonstrate feasibility and scientific merit. The LOI acceptance is based on several factors, including the scientific merit of the submission, the ability of the DDT to address a specified drug development need, the availability of supporting information and resources, and the feasibility and practicality of implementation.