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. 2025 Mar;33(2):252-257.
doi: 10.1038/s41431-024-01586-y. Epub 2024 Mar 12.

Origin and evolution of pentanucleotide repeat expansions at the familial cortical myoclonic tremor with epilepsy type1 - SAMD12 locus

Xinhui Chen #  1 , Fan Zhang #  1 , Yihua Shi #  1 , Haotian Wang  1 , Miao Chen  2 , Dehao Yang  1 , Lebo Wang  1 , Peng Liu  3 , Fei Xie  4 , Jiawen Chen  1 , Aisi Fu  5 , Ben Hu  6 , Bo Wang  1 , Zhiyuan Ouyang  1 , Sheng Wu  1 , Zhiru Lin  1 , Zhidong Cen  7 , Wei Luo  8
Affiliations

Origin and evolution of pentanucleotide repeat expansions at the familial cortical myoclonic tremor with epilepsy type1 - SAMD12 locus

Xinhui Chen et al. Eur J Hum Genet. 2025 Mar.

Abstract

Familial cortical myoclonic tremor with epilepsy type 1 (FCMTE1) is caused by (TTTTA)exp(TTTCA)exp repeat expansions in SAMD12, while pure (TTTTA)exp is polymorphic. Our investigation focused on the origin and evolution of pure (TTTTA)exp and (TTTTA)exp(TTTCA)exp at this locus. We observed a founder effect between them. The phylogenetic analysis suggested that the (TTTTA)exp(TTTCA)exp might be generated from pure (TTTTA)exp through infrequent transformation events. Long-read sequencing revealed somatic generation of (TTTTA)exp(TTTCA)exp from pure (TTTTA)exp, likely via long segment (TTTCA) repeats insertion. Our findings indicate close relationships between the non-pathogenic (TTTTA)exp and the pathogenic (TTTTA)exp(TTTCA)exp, with dynamic interconversions. This sheds light on the genesis of pathogenic repeat expansions from ancestral premutation alleles. Our results may guide future studies in detecting novel repeat expansion disorders and elucidating repeat expansion mutational processes, thereby enhancing our understanding of human genomic variation.

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Conflict of interest statement

Competing interests: The authors declare no competing interests. Ethical approval: The ethics was approved in the Second Affiliated Hospital, Zhejiang University School of Medicine (I2019001151). Written informed consent was obtained from all participants following the Declaration of Helsinki.

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