NOTCH2NLC trinucleotide interruptions are associated with cognitive impairment in neuronal intranuclear inclusion disease (NIID)

Background Abnormal GGC expansion within the NOTCH2HLC gene causes neuronal intranuclear inclusion disease (NIID), a rare neurodegenerative disease with variable clinical manifestations, including cognitive dysfunction. In addition to GGC repeats, there are two forms of repeated interruptions, GGA and AGC, within NOTCH2NLC repeats. Previous studies reported fewer GGA and more AGC interruptions in patients with Parkinson Disease; fewer GGA and AGC interruptions in patients with essential tremor, compared to NIID patients. These results suggest that trinucleotide interruptions within the NOTCH2NLC GGC repeats could influence the phenotype of disease, although the mechanism is not known. Methods We looked at the repeat compositions in NOTCH2NLC in NIID patients with and without cognitive impairment (CI). NOTCH2NLC repeats were screened by long‐read sequencing on the Oxford Nanopore platform. Results In 13 NIID patients with NOTCH2NLC repeat expansion, 9 (69%) presented with CI. Patients with CI were older [mean (SD) = 69.7 (5.8) vs 63.3 (7.2)], had later age at onset [63.2 (6.5) vs 59.8 (7.1)] and longer disease duration [6.9 (5.2) vs 3.5 (3.9)] than patients without CI. The NOTCH2NLC repeats range from 89‐138 repeats in patients with CI; 82‐166 repeats in patients without CI. Patients with CI carried more GGC repeats [97.7 (1.7) vs 92.8 (9.0)] and less GGA [0.8 (1.3) vs 2.2 (2.8)] and AGC [0.6 (1.0) vs 3.5 (7.4)] interruptions within NOTCH2NLC, compared to patients without CI. Conclusion Our results suggest that NIID patients with cognitive impairment have a purer GGC repeat in NOTCH2NLC compared to patients without cognitive impairment, supporting previous studies that repeat interruptions may modify clinical manifestation of NIID.