PPIB and Schnyder corneal dystrophy: A previous study of Canadian children with SCD supplemented with 1 mg/d folic acid (n = 92) reported that multiple serum nutrient insufficiencies/deficiencies were present in individuals, with zinc (<age- and sex-specific cut-offs) and vitamin D (<50 nmol/L) insufficiency being common (52 and 57%, respectively), vitamin B-6 deficiency (<20 nmol/L) being evident in a small minority of children (3%), but none of the children presenting with folate (<11 nmol/L) or vitamin B-12 deficiency (<133 pmol/L) (14).