Defendant also failed to preserve for our review his contention that the testimony of the expert was improperly utilized to prove that the charged crimes occurred and to bolster the victim's testimony. We agree with defendant, however, that the challenged testimony was improperly admitted, inasmuch as it was introduced primarily to prove that the charged crimes took place (see People v Knupp, 179 AD2d 1030, 1031-1032 [4th Dept 1992]), and we conclude that the error in its admission "operated to deprive defendant of a fair trial and thus warrant[s] reversal in the interest of justice" (id. at 1032; see CPL 470.05 [6] [a]). In reaching that conclusion, we acknowledge that expert testimony concerning CSAAS and similar psychological syndromes has long been admissible to explain the behavior of a victim that might be puzzling to a jury (see People v Spicola, 16 NY3d 441, 465 [2011], cert denied 565 US 942 [2011]).

Moreover, the court's supplemental instructions to the jury did not render duplicitous defendant's conviction of assault in the second degree under count six of the indictment (see generally, People v Keindl, 68 N.Y.2d 410, 417-418, rearg denied 69 N.Y.2d 823; People v Charles, 61 N.Y.2d 321, 327-328). The admission of expert testimony regarding rape trauma syndrome, learned helplessness syndrome and battered woman syndrome was proper "to explain behavior on the part of the [complainant] that might seem unusual to a lay jury unfamiliar with the patterns of response exhibited" by a person who has been physically and sexually abused over a period of time (People v Bennett, 79 N.Y.2d 464, 471; see, People v Taylor, 75 N.Y.2d 277, 292-293; cf., People v Knupp, 179 A.D.2d 1030). Contrary to the contention of defendant, that testimony did not bear "solely on proving that a [kidnapping] had occurred" (People v Bennett, supra, at 473).

We further reject defendant's contention that the testimony of the People's psychologist regarding the hesitancy of child sexual abuse victims to disclose abusive conduct constituted improper bolstering. Such testimony was proper under the well-established rule that expert testimony regarding the behavior of a sexual abuse victim, if generally accepted in the scientific community, is admissible (see, People v. Bennett, 79 N.Y.2d 464; People v Taylor, 75 N.Y.2d 277; People v. Keindl, 68 N.Y.2d 410, rearg denied 69 N.Y.2d 823; cf., People v. Knupp, 179 A.D.2d 1030). The opinion of the People's psychologist was properly based upon his own observations as well as upon the theories of well-known experts in the field of child sexual abuse (see, People v Sugden, 35 N.Y.2d 453, 460-461).

We do not find, as urged by defendant, that the verdict was against the weight of the evidence; nevertheless, because defendant was deprived of a fair trial by the improper admission of expert testimony, we reverse and remit for a new trial. Expert testimony regarding rape trauma syndrome, abused child syndrome or the like may be admitted only "to explain [the victim's] behavior that might appear unusual" or that jurors might not be expected to understand (People v Taylor, 75 N.Y.2d 277, 293). For example, in People v Keindl ( 68 N.Y.2d 410) expert testimony was permitted "to rebut defendant's attempt to impair the credibility of [sexually abused children] by evidence that they had not promptly complained" of the abuse (People v Taylor, supra, at 288; see, People v Bennett, 169 A.D.2d 369, 374, affd 79 N.Y.2d 464; see also, People v Knupp, 179 A.D.2d 1030, 1031-1032). Here, as part of their case in chief, the People made an offer of proof which indicated that the proffered testimony of the social worker would have two purposes: to explain the victims' failure to promptly report the abuse to any authority figures, and "to show the manifestations of sexual abuse that the youngsters exhibit". It is this latter purpose, to which most of the testimony was actually directed, which we find impermissible.

The prejudicial nature of such testimony becomes readily apparent when one considers that the one count of rape in the third degree of which the defendant was convicted alleged an incident that occurred just five or six months before the complainant left the defendant's house to live elsewhere. In sum, Wohl's testimony, taken as a whole, was to the effect that the symptoms exhibited by the complainant, as well as the delayed onset of those symptoms, were consistent with patterns of response exhibited by proven child sexual abuse victims. Under the facts of this case, there was no reason to introduce this testimony, other than to prove that the alleged acts of child sexual abuse occurred (see, People v Banks, supra; see also, People v Bennett, 79 N.Y.2d 464, 473; People v Knupp, 179 A.D.2d 1030). We also find the admission of testimony concerning prior uncharged sexual abuse to be erroneous. While this claim was not preserved for appellate review (see, People v Udzinski, 146 A.D.2d 245), we find the error to be extremely prejudicial and, therefore, review the claim in the exercise of our interest of justice jurisdiction.

People v Taylor (supra) is authority for the recognition of a child sexual abuse syndrome where a female child was sodomized or otherwise sexually abused, but not raped. (People v Califano, 216 A.D.2d 574, 575, lv denied 86 N.Y.2d 791; People v Sansevero, 185 A.D.2d 256; People v Knupp, 179 A.D.2d 1030 [syndrome recognized but conviction reversed because expert testimony introduced to prove crime took place].) Expert testimony of child sexual abuse syndrome has been accepted in cases where the victim is male as well.

In People v Graydon ( 43 A.D.2d 842, 843 [2d Dept 1974]), the Court held, in reversing a judgment of conviction for manslaughter, that "it was highly prejudicial for the People to elicit testimony on redirect examination from their expert psychiatric witness to the effect that he had found defendant's version incredible and for the witness to explain the reason for that conclusion to the jury." (See also, People v Knupp, 179 A.D.2d 1030.) V