|Number of repeats||Counts (alleles)||Percentage|
Overview of repeats
Neuronal intranuclear inclusion disease (NIID) is a neurological disease inherited in an autosomal dominant manner, although around two thirds of cases have been found to be sporadic (Ishiura et al., 2019; Sone et al., 2016). It was described by two research groups that GGC repeats in the 5′ UTR of NOTCH2NLC gene are causing the disease (Ishiura et al., 2019; Nakamura et al., 2020). Ishiura and colleagues found that in 28 patients, the expansion was in the range of 90-180 repeats. In the control group they did not see any expansions and in 182 unaffected individuals, the repeat range was between 7 and 39 repeats (Ishiura et al., 2019). This was confirmed by another study a year later showing 330-520 bp repeat length (corresponding to 110-173 trinucleotide repeats) in seven NIID patients (Nakamura et al., 2020).
In addition, expansions in NOTCH2NLC gene are also suggested to be the genetic cause for the hereditary essential tremor type 6 (ETM6), which was found in 11 families (Sun et al., 2020). The repeat length in affected individuals from mainland China was determined to be between 60 and 250 repeats, whereas in the control group it was between 4 to 41 repeats (Sun et al., 2020).