Deus Ex: Human Revolution has no in-built mouse acceleration, but (due to badly coded free look) a lot of players have reported a problem similar to lag caused by mouse acceleration.
Here's how to fix it on Windows:
1. Use a registry fixing tool e.g. Regedit
2. Navigate to "HKEY_CURRENT_USER\Software\Eidos\Deus Ex: HR
3. Change the value of g_debugFreeLookSpeedScalingRatio_Pitch from 6e 00 00 00 to 00 00 00
4. Change the value of g_debugFreeLookSpeedScalingRatio_Yaw from 86 00 00 00 to 00 00 00 00
5. Re-adjust your mouse speed in game, no acceleration