1Green, R & Miller, JW (2007) Vitamin B12. In Handbook of Vitamin, chapter 13 [Zempleni, J, Rucker, RB, McCormick, DB and Suttie, JW, editors]. Boca Raton, FL: CRC Press.
2Rosenblatt, DS & Fenton, WA (2001) Inherited disorders of folate and cobalamin transport and metabolism. In The Metabolic and Molecular Basis of Inherited Metabolic Disease, 8th ed., chapter 155, pp. 3897–3933 [Scriver, CR, Beaudet, AL, Sly, WS and Valle, D, editors]. New York: McGraw-Hill.
3Hazra, A, Kraft, P, Selhub, J, et al. (2008) Common variants of FUT2 are associated with plasma vitamin B12 levels. Nat Genet 40, 1160–1162.
4Hazra, A, Kraft, P, Lazarus, R, et al. (2009) Genome-wide significant predictors of metabolites in the one-carbon metabolism pathway. Hum Mol Genet 18, 4677–4687.
5Garrod, A (1931) The Inborn Factors in Disease. Facsimile of 1931 Edition. New York: Oxford University Press.
6Coelho, D, Suormala, T, Stucki, M, et al. (2008) Gene identification for the cblD defect of vitamin B12 metabolism. N Engl J Med 358, 1454–1464.
7Froese, DS & Gravel, RA (2011) Genetic disorders of vitamin B12 metabolism: eight complementation groups–eight genes. Expert Rev Mol Med 29, e37.
8Moayyeri, A, Hammond, CJ, Valdes, AM, et al. (2012) Cohort Profile: TwinsUK and Healthy Ageing Twin Study. Int J Epidemiol 41, 1–10.
9Beggs, MJ, Sohn, LJ, Herrmann, RJ, et al. (1995) Folate Immunoassay Utilizing Folate Binding Protein in a Multiclonal Antibody Format. Abbott Park, IL: United States Abbott Laboratories.
10Ubbink, J, Hayward Vermaak, WJ & Bissbort, S (1991) Rapid high performance liquid chromatographic assay for total homocysteine levels in human serum. J Chromatogr 565, 441–446.
11Stata (2009) Stata/MP 11 for Mac. College Station, TX: StataCorp LP.
12Barber, MJ, Cordell, HJ, MacGregor, AJ, et al. (2004) Gamma regression improves Haseman–Elston and variance components linkage analysis for sib-pairs. Genet Epidemiol 26, 97–107.
13Neale, M & Cardon, L (1992) Methodology for Genetic Studies of Twins and Families. Dordrecht: Kluwer Academic Publishers.
14DeFries, J & Fulker, D (1985) Multiple regression analysis of twin data. Behav Genet 15, 467–473.
15Weale, ME (2010) Quality control for genome-wide association studies. Methods Mol Biol 628, 341–372.
16Barrett, JC, Fry, B, Maller, J, et al. (2005) Haploview: analysis and visualization of LD and haplotype maps. Bioinformatics 21, 263–265.
17Aulchenko, YS, Ripke, S, Isaacs, A, et al. (2007) GenABEL: an R library for genome-wide association analysis. Bioinformatics 23, 1294–1296.
18Falconer, DS & Mackay, TFC (1996) Introduction to Quantitative Genetics, 4th ed.Harlow, Essex: Addison Wesley Longman.
19Andrew, T, Hart, DJ, Snieder, H, et al. (2001) Are twins and singletons comparable? A study of disease-related and lifestyle characteristics in adult women. Twin Res 4, 464–477.
20Baik, HW & Russell, RM (1999) Vitamin B12 deficiency in the elderly. Annu Rev Nutr 19, 357–377.
21Hopper, JL (1999) Why “common environmental effects” are so uncommon in the literature. In Advances in Twin and Sib-pair Analysis, pp. 151–166. London: Oxford University Press.
22Nilsson, SE, Read, S, Berg, S, et al. (2009) Heritabilities for fifteen routine biochemical values: findings in 215 Swedish twin pairs 82 years of age or older. Scand J Clin Lab Invest 69, 562–569.
23Paré, G, Chasman, DI, Parker, AN, et al. (2009) Novel associations of CPS1, MUT, NOX4, and DPEP1 with plasma homocysteine in a healthy population: a genome-wide evaluation of 13,974 participants in the Women's Genome Health Study. Circ Cardiovasc Genet 2, 142–150.
24Ames, BN, Elson-Schwab, I & Silver, EA (2002) High-dose vitamin therapy stimulates variant enzymes with decreased coenzyme binding affinity (increased K(m)): relevance to genetic disease and polymorphisms. Am J Clin Nutr 75, 616–658.