SIX1 and microtia: Then, there are some genes involved or indirectly involved in syndromic forms such as: ROBO1/ROBO2; SIX1/SIX5, which is linked to branchio-oto-renal (BOR) syndrome where microtia is a key feature; and CHUK, involved in embryogenesis and whose mutations can lead to developmental abnormalities, including ear defects [21].