Background GGC repeat expansion in NOTCH2NLC has been recently linked to neuronal intranuclear inclusion disease (NIID) via unknown disease mechanisms. Herein, we explore the genetic origin of the sporadic cases and toxic RNA gain-of-function mechanism in NIID.
Methods Multiple genetic screenings were performed on NIID individuals and their available family members. Methylation status of blood DNA, NOTCH2NLC mRNA level from muscle biopsies and RNA foci from skin biopsies of NIID individuals or asymptomatic carriers were evaluated and compared.
Results In two sporadic NIID families, we identified two clinically and pathologically asymptomatic fathers carrying large GGC repeat expansion, above 300 repeats, with offspring repeat numbers of 172 and 148, respectively. Further evaluation revealed that the GGC repeat numbers in the sperm from two asymptomatic fathers were only 63 and 98, respectively. The CpG island in NOTCH2NLC of the asymptomatic carriers was hypermethylated, and accordingly, the NOTCH2NLC mRNA levels were decreased in the asymptomatic fathers. GGC repeat expansion RNA formed RNA foci and sequestered RNA binding proteins into p62 positive intranuclear inclusions in NIID individuals but not in the control or asymptomatic carrier.
Conclusion Our study suggested the GGC repeat expansion in NOTCH2NLC might have a disease-causing number ranging from ~41 to ~300 repeats. The contraction of GGC repeat expansion in sperm could be a possible mechanism for the paternal-biased origin in some sporadic or recessive inherited NIID individuals. The toxic RNA gain-of-function mechanism was identified to be involved in the pathogenicity of this disease.
- genetic carrier screening
- genetic counselling
- neurodegenerative diseases
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JD and BZ contributed equally.
Contributors SY, ZW and DH conceived the idea, designed studies and supervised the project; JD, BZ and JY designed and carried out experiments, and analysed data; XG and PL analysed the long-read whole-genome sequencing data; XH, JF, XL, XX, MZ, YZ, QW, JL, WZ, YY, SY, ZW and DH contributed to the clinical diagnosis and biopsy; JD, ZW and DH wrote and edited the manuscript. All authors read and approved the final manuscript.
Funding The work was supported by the National Natural Science Foundation of China (No. 81571219, 82071409 and U20A20356 to ZW), Double Thousand Talents Programme of Jiangxi province (jxsq2019101021 to DH), Science and Technology Project of Jiangxi Health Committee (202110028 to DH) and Peking University Medicine Fund of Fostering Young Scholars’ Scientific & Technological Innovation (to JD).
Competing interests None declared.
Patient consent for publication Parental/guardian consent obtained.
Ethics approval All clinical materials used in this study were obtained for diagnostic purpose with written informed consent. The study was approved by the Ethics Committee of the First Hospital of Peking University 2019 .
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available on reasonable request. The data used and analysed during the current study available from the corresponding author on reasonable request.
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