ETHE1 and ethylmalonic encephalopathy: They appear to have better prognosis than other syndromes caused by genes implied in complex IV metabolism, such as ETHE1 and LRPPRC. The ETHE1 is related to ethylmalonic encephalopathy (OMIM #602473) and may manifest as LS due to accumulation of sulfide, which reduces complex IV functioning and justifies the resemblance.