Geraldo Lopez-Topete appeals the sentence imposed by the district court1 after he pleaded guilty to one count of interstate travel in aid of unlawful activity, in violation of 18 U.S.C. § 1952(a)(3). In a brief filed under Anders v. California, 386 U.S. 738, 87 S.Ct. 1396, 18 L.Ed.2d 493 (1967), Lopez-Topete challenges the denial of a downward departure motion based on diminished mental capacity. This argument amounts to an attack on the district court’s discretionary refusal to depart downward, which in the circumstances of this case is unreviewable. See United States v. Gonzalez-Ramirez, 350 F.3d 731, 734 (8th Cir. 2003).

Having reviewed the record independently under Penson v. Ohio, 488 U.S. 75, 109 S.Ct. 346, 102 L.Ed.2d 300 (1988), we find no nonfrivolous issues. Accordingly, we affirm. We also grant counsel’s motion to withdraw.