We further ‘split’ two previously grouped (‘lumped’) disorders into five separate disease entities: 1) Coenzyme Q5 methyltransferase deficiency, 2) Coenzyme Q8A (ADCK3) deficiency, 3) Methylmalonic aciduria and homocystinuria, cblD type, 4) Homocystinuria, cblDv1 type, 5) Methylmalonic aciduria, cblDv2 type. The gene discussed is COQ8A; the disease is homocystinuria.