Neuronal intranuclear inclusion disease (NIID) is a rare, progressive neurodegenerative disorder currently diagnosed through invasive biopsies or genetic testing with ethnic limitations. Existing biomarkers from cerebrospinal fluid or plasma are not fully noninvasive, and no urine‐based biomarker has been identified. There is an urgent need for a noninvasive, definitive diagnostic tool to distinguish NIID from other neurodegenerative diseases and healthy individuals. We developed a homogeneous digital immunoassay using two‐color quantum dot (QD)‐labeled antibodies to quantify p62 in urinary cell nuclei, achieving a detection limit of 47 fM. The assay demonstrated high selectivity and a wide dynamic range across three orders of magnitude. Analysis of urine samples from 10 NIID patients, 4 healthy controls, and 13 patients with other neurodegenerative disorders (myasthenia gravis, cerebral infarction, and Parkinson's disease) revealed that p62 levels were significantly elevated only in NIID patients. Spike recovery tests confirmed measurement accuracy (91%–106%), and p62 levels showed no correlation with disease stage in this limited cohort. This study introduces the first noninvasive urinary biomarker for NIID using a novel homogeneous digital immunoassay. The significantly elevated p62 levels specifically in NIID patients highlight its potential as a reliable, noninvasive diagnostic tool, enabling distinction from other neurodegenerative conditions and facilitating earlierand more accessible diagnosis.
Ye et al. (Sun,) studied this question.