Due to the crucial role of Oxa1 in the assembly of OXPHOS complexes, biallelic variants in OXA1L (p.S170Qfs*18 and p.C207F) in a patient caused a profoundly decreased level of OXPHOS complexes I, IV, and V, which leads to severe illness with hypotonia, severe encephalopathy, and developmental delay in early childhood (Thompson et al., 2018). The gene discussed is OXA1L; the disease is Global developmental delay.