Overview of repeats

Insertions of pentanucleotide TTTCA repeats into the intron 4 of the SAMD12 gene has been shown to be responsible for familial adult myoclonic epilepsy type 1 (FAME1) disease that has been recently described by a few different research groups. The first published study that reported pathogenic TTTCA expansions in FAME 1, 6 and 7 was conducted by Ishiura and colleagues (2018). They showed that the insertion of expanded TTTCA repeats were present in all patients in conjunction with TTTTA repeats. The range of expansions for TTTCA and TTTTA combined was estimated to be in the range of 440 to 3680 repeats. For example, one patient had 598 repeats of TTTTA and 458 repeats of TTTCA. In 82 patients the configuration of expansion was determined to be: (TTTTA)_exp(TTTCA)_exp and in three patients from one family it was as follows: (TTTTA)_exp(TTTCA)_exp(TTTTA)_exp. They did not see any expansions of TTTCA repeats in controls, but in 5.9% of healthy individuals they observed expansions of TTTTA, suggesting that TTTTA does no contribute to the disease (Ishiura et al., 2018). Two other studies investigating Chinese cohorts has been published as well, which reported that the disease-causing repeat length can be as low as 100 of TTTCA (Cen et al., 2018; Lei et al., 2019)

→ View STRipy's population-wide repeat data for SAMD12 locus