The Relationship Between GGC Repeat Expansion In The NOTCH2NLC Gene And Amyotrophic Lateral Sclerosis

Background:Amyotrophic lateral sclerosis(ALS)and neuronal intranuclear inclusion body disease(NIID)are two related neurodegeneration diseases with overlaps in clinical phenotypes and are both clinically and genetically heterogeneous.For example,ALS is similar to NIID muscle weakness–dominant subtype(NIID-M)in clinical manifestations of which have muscle weakness atrophy.Moreover,intranuclear inclusions positive for ubiquitin and p62 have been reported in both ALS and NIID.In addition,proteins associated with ALS have also been detected in nuclear inclusions of patients with NIID,such as FUS and OPTN.Thus,we suggest that the GGC repeats in NOTCH2 NLC may contribute to ALS.Objective : To determine whether the GGC repeats in the NOTCH2 NLC gene contribute to ALS.Methods:Our study recruited 545 patients with ALS and 1305 healthy controls from mainland China.Pathogenic mutations in known ALS-causative genes were excluded.Repeat-primed polymerase chain reaction(RP-PCR)and GC-rich PCR were performed to determine the GGC repeat length in NOTCH2 NLC.Systematic and targeted clinical evaluations and investigations,including skin biopsy and dynamic neurophysiological studies,were conducted in the patients carrying abnormal GGC repats expansion in NOTCH2 NLC gene.Results:GGC repeat expansion in NOTCH2 NLC gene was observed in four patients(numbers of repeats 44,54,96,and 143),accounting for0.73%(4/545)of all patients with ALS.Moreover,GGC repeat expansion in NOTCH2 NLC gene was not detected in healthy controls(0/1,305).A comparison with 1305 healthy controls revealed that GGC repeat expansion in NOTCH2 NLC was associated with ALS(Fisher exact test,4/545 vs 0/1,305,p = 0.007).Compared to patients with the NIID-M,patients with ALS phenotype carrying the abnormal repeat expansion tended to have a severe phenotype and rapid deterioration.Skin biopsy revealed typical eosinophilic,p62-positive,ubiquitin-positive intranuclear inclusions,and electron microscopy also revealed intranuclear inclusions with no membranes in two ALS patients carrying abnormal GGC repats expansion in NOTCH2 NLC gene.Conclusion:Our results suggest that ALS is a specific phenotype of NIID.