TMEM126B and Luscan-Lumish syndrome: Our findings uncovered the functional effect and the molecular mechanism of the pathogenic TMEM126B variants c.82-2 A > G and c.290dupT, which not only expand the gene mutation spectrum of LLS, but also expand the clinical spectrum caused by TMEM126B mutations, thus contributing to the clinical diagnosis of TMEM126B mutation-related mitochondrial diseases.