Heterogenous Genetic, Clinical, and Imaging Features in Patients with Neuronal Intranuclear Inclusion Disease Carrying NOTCH2NLC Repeat Expansion

Abstract

Neuronal intranuclear inclusion disease (NIID) is a neurodegenerative disorder that is caused by the abnormal expansion of non-coding trinucleotide GGC repeats in NOTCH2NLC. NIID is clinically characterized by a broad spectrum of clinical presentations. To date, the relationship between expanded repeat lengths and clinical phenotype in patients with NIID remains unclear. Thus, we aimed to clarify the genetic and clinical spectrum and their association in patients with NIID. For this purpose, we genetically analyzed Japanese patients with adult-onset NIID with characteristic clinical and neuroimaging findings. Trinucleotide repeat expansions of NOTCH2NLC were examined by repeat-primed and amplicon-length PCR. In addition, long-read sequencing was performed to determine repeat size and sequence. The expanded GGC repeats ranging from 94 to 361 in NOTCH2NLC were found in all 15 patients. Two patients carried biallelic repeat expansions. There were marked heterogenous clinical and imaging features in NIID patients. Patients presenting with cerebellar ataxia or urinary dysfunction had a significantly larger GGC repeat size than those without. This significant association disappeared when these parameters were compared with the total trinucleotide repeat number. ARWMC score was significantly higher in patients who had a non-glycine-type trinucleotide interruption within expanded poly-glycine motifs than in those with a pure poly-glycine expansion. These results suggested that the repeat length and sequence in NOTCH2NLC may partly modify some clinical and imaging features of NIID.

Keywords: GGC repeat expansion; NOTCH2NLC; clinical presentations; genotype–phenotype correlation; neuroimaging; neuronal intranuclear inclusion disease.

Figure 1

Expanded repeat sequences in NOTCH2NLC. Repeat length and sequence were determined by Nanopore long-read sequencer. In Pt 7, the expanded GGC repeats (n = 107) were followed by two GGA sequences in allele 1. In allele 2, the expanded GGC repeats (n = 112) were interrupted by three AGC motifs, followed by two GGA sequences. In Pt 14, GGG, GCA, CGC, and GCG sequences were inserted within the expanded GGC repeats (n = 109) in allele 1. In allele 2, a unique trinucleotide sequence containing expanded TTA (n = 76), GAT (n = 125), and GGC repeats (n = 44) was observed.

Figure 2

Characteristic MRI findings. Representative MRI images in Pt 1 (A–C), Pt 2 (D–F), Pt 3 (G–I), Pt 7 (J–L), and Pt 14 (M–O) were shown. High-intensity lesions of various degrees along with the U-fibers were observed on DWI (A,D,G,J,M). High-intensity lesions in the middle cerebellar peduncles (B) and paravermal lesions (E,K) appeared as cerebellar abnormalities on FLAIR. Bilateral white matter changes of various degrees were detected in all patients (C,F,I,L,O). DWI: diffusion-weighted image; FLAIR: fluid attenuated inversion recovery.

Figure 3

Effect of non-glycine type trinucleotide interruption on phenotype. Association of non-glycine type trinucleotide interruption with age at onset (A), MMSE (B), and ARWMC scores (C) was examined. Patients with non-glycine type trinucleotide interruption has a significantly larger ARWMC score than those without (C). *, p < 0.05.