 For example, PS’s mother also had lexical gustatory synesthesia.One study suggests that there could be some sort of synesthesia gene passed through families that encodes for a predisposition to synesthesia but not necessarily its expression.Further studies into determining the exact synesthesia gene have not been successful, but it is possible that the over-expression of the serotonin 2A receptor on chromosome 13 resulting in a high receptor density could be the cause.