Is there a defense to a claimed defense to the parents' cause of action?

Defendant did tie his factual showing to a claimed defense to the parents' cause of action. The claim is premised on the theory the parents can recover only for mental distress if it is engendered by a shock received at the time of the birth of the child. To be actionable, he presupposes the shock must derive from the contemporaneous perception of the birth and the genetic defect, an issue which can be resolved upon the sole undisputed fact. Defendant's characterization of the parental cause of action derives from a line of case law commencing with Dillon v. Legg (1968) 68 Cal.2d 728, 69 Cal.Rptr. 72, 441 P.2d 912. An analysis of this case law is the path which leads to the conclusion we reach.