<unk>  is an autosomal dominant metabolic disorder that causes a deficiency of the enzyme tetrahydrofolate-methyltransferase; affected individuals cannot properly metabolize methylcobalamin, a type of Vitamin B12.
Arakawa's syndrome II
Pascual-Castroviejo syndrome type 1
Gómez–López-Hernández syndrome
Urban–Rogers–Meyer syndrome
Havana syndrome
Löffler's syndrome
Grisel's syndrome
Townes–Brocks syndrome