FRMD4B and Duane retraction syndrome: Finally, syndromic sporadic DRS proband ENG_OA harbored a homozygous FRMD4B variant (c.380A>G, p.(Lys127Arg), ENST00000398540.8) located in the Band 4.1 domain, which is involved in cytoskeletal-membrane linkage (Fig. 8U, Supplementary Figure 4B).24 She had left-sided exotropic DRS type III characterized by impaired abduction and adduction, globe retraction in adduction, and upshoot.