Biochemical but not clinical vitamin A deficiency results from mutations in the gene for retinol binding protein - Biesalski, H K; Frank, J; Beck, S C; Heinrich, F; Illek, B; Reifen, R; Gollnick, H; Seeliger, M W; Wissinger, B; Zrenner, E (Am J Clin Nutr, 1999)