SLC6A4 and psychiatric disorder: Furthermore, there are also increasing suggestions that the role of the SLC6A4 polymorphisms may be more pronounced during embryogenesis and development, thus raising the possibility that disrupting normal maturation of certain neuronal networks critical for normal adult functions, will influence behaviour and increase vulnerability to psychiatric disorders in adults (Caspi et al. 2003; Ansorge et al. 2004; Parsey et al. 2006).