The Ser 460 to Pro substitution of the protein S alpha (PROS1) gene is a frequent mutation associated with free protein S (type IIa) deficiency - Duchemin, J; Gandrille, S; Borgel, D; Feugard, P; Alhenc-Gelas, M; Matheron, C; Dreyfus, M; Dupuy, E; Juhan-Vague, I; Aiach, M (Blood, 1995)