SYNJ1 and Mental deterioration: Clinical features in SNCA triplication carriers are similar to the VPS13C-related phenotype (63, 148), while the complex phenotype of SNCA p.G51D patients, characterized by precocious disease onset, pyramidal signs, myoclonus, seizures, and, inconstantly, cognitive decline, significantly overlaps with DNAJC6- and SYNJ1-related phenotypes (82, 155, 157–160).