Juvenile cobalamin deficiency in individuals of African ancestry is caused by a founder mutation in the intrinsic factor gene GIF.
Ament AE, Li Z, Sturm AC, Perko JD, Lawson S, Masterson M, Quadros EV, Tanner SM. Br J Haematol. 2009 Feb; 144(4):622-4. Epub 2008 Nov 19.