Combined with the structural information on Bcs1 and available phenotypes of pathogenic mutations, it has been proposed that the structural integrity of Bcs1-specific region is critical for persevering the proton motive force across the IM, and the fetal GRACILE syndrome could be the result of proton leakage caused by defective Bcs1-specific domain on top of the failed cyt bc1 complex assembly (Tang et al., 2020). Here, BCS1L is linked to GRACILE syndrome.