Hiroki Yamazaki

We report a 58‐year‐old woman with a novel splice‐site variant in the TANK‐binding kinase 1 ( TBK1 :c.993–2A>C p.Ala332TyrfsTer39) who sequentially developed primary lateral sclerosis (PLS) followed by right temporal variant frontotemporal dementia (rtvFTD). Neuroimaging demonstrated right anterior temporal atrophy before cognitive symptoms, and prosopagnosia represented the earliest manifestation of rtvFTD. Molecular analysis revealed reduced levels of correctly spliced TBK1 transcripts, consistent with haploinsufficiency. Given the shared involvement of TDP‐43 pathology in both PLS and rtvFTD, this case indicates TBK1 dysfunction as a fundamental genetic factor underlying the coexistence of these phenotypes, underscoring the clinical value of early neuroimaging and genetic evaluation.

Repeat expansion diseases, particularly those involving GC-rich motifs, have been increasingly recognized as contributors to neurological and neuromuscular disorders. Amyotrophic lateral sclerosis (ALS) has been linked to several such expansions, including intermediate-length repeats in genes implicated in oculopharyngodistal myopathy (OPDM). To investigate the possible involvement of CGG repeat expansions in ALS, 424 ALS patients and 312 controls of Japanese descent were screened for expansions in five genes associated with repeat expansion disorders, namely GIPC1 , RILPL1 , FMR1 , AFF2 , and NUTM2BAS1 . Repeat-primed PCR and fragment analysis revealed that four ALS patients exhibited abnormal CGG expansions in GIPC1 (33–55 repeats), whereas two control individuals harbored expanded alleles (67 and 83 repeats). No expansions in the other genes were detected. Long-read sequencing confirmed repeat sizes and showed sequence instability. Histopathological analysis of ALS patients with GIPC1 expansion demonstrated classical ALS pathology, including phosphorylated TDP-43-positive inclusions. RNA fluorescence in situ hybridization revealed nuclear foci containing GIPC1 repeat RNA exclusively in ALS patients with GIPC1 expansions, suggesting RNA-mediated toxicity. These findings indicate that a subset of ALS patients present with intermediate CGG expansions in GIPC1 , which may represent a novel pathogenic mechanism analogous to other noncoding repeat disorders. Given that GIPC1 full expansions are associated with OPDM, these results support the hypothesis of a pathological continuum between neurodegeneration and myopathy driven by repeat length and sequence context. Nonetheless, further investigations into the potential of GIPC1 CGG expansions as genetic risk factors or modifiers in ALS are warranted.