Homozygous and compound heterozygous pathogenic variants in PTCD3 cause the combined oxidative phosphorylation deficiency 51 (COXPD51), for which symptoms include respiratory insufficiency, nystagmus, delayed psychomotor development, brain lesions, bilateral hearing loss, and optic atrophy (OMIM #619057) [30]. Here, PTCD3 is linked to pathologic nystagmus.