|Number of repeats||Counts (alleles)||Percentage|
Overview of repeats
Oculopharyngodistal myopathy (OPDM) is a rare neuromuscular disease and around 200 affected individuals have been found to date since 1977 (Deng et al., 2020). The article by Ishiura and colleagues investigating repeats in the LRP12 gene was shortly followed by another study conducted by Deng et al. (2020) that examined Chinese and Japanese individuals. In these patients, repeat expansions in the 5′ UTR of the GIPC1 gene was discovered and this was associated with OPDM as well, followed by naming the disease as type 2 (OPDM2). In 12 out of 24 affected individuals from Chinese cohort and 7 out of 194 patients from Japanese cohort had expansions in the GIPC1 gene, ranging from 88-164 for the Chinese and 73-161 for the Japanese cohort. No expansions were detected in any of the controls. The range of GGC repeats in 550 control subjects was determined to be between 12-32 (Deng et al., 2020).
In the same research, it was suggested that expansions in two different genes could cause OPDM through shared pathogenesis. Interestingly, one unaffected individual with over 500 GGC repeats in 5′ UTR of the GIPC1 gene was discovered, whose both offspring, with 117 and 113 repeats, were symptomatic. That raises a possibility where a certain range of repeats can cause a disease, similarly to CGG repeats in the FMR1 gene whereby 55-199 repeats causes FXTAS while 200 and more repeats results in FXS. More research is needed to confirm this (Deng et al., 2020).