Although there are no REDs linked to FGF3 STRs described here, the only known disease caused by the expansion of intronic (CCTG·CAGG) tetra-nucleotide repeats is myotonic dystrophy 2 (DM2), one of the two most common forms of muscular dystrophy (Koscianska et al., 2021). The gene discussed is FGF3; the disease is Proximal myotonic myopathy.