SIX1 and BOR syndrome: Since EYA1 was identified as the initial BOR/BO syndrome gene6,7, more loci have been mapped within the SIX gene family, including SIX18 and SIX5. Although EYA1 pathogenic variants are the primary cause6,7, affecting 40–75% of patients, SIX1 accounts for 3.0–4.5% of cases8,9.