- The codon 620 tryptophan allele of the lymphoid tyrosine phosphatase (LYP) gene is a major determinant of Graves' disease. Velaga, M.R., Wilson, V., Jennings, C.E., Owen, C.J., Herington, S., Donaldson, P.T., Ball, S.G., James, R.A., Quinton, R., Perros, P., Pearce, S.H. J. Clin. Endocrinol. Metab. (2004)