Erreur syntax

   function demande_existe()
   {
   $count_user = 0;
   $bdd = new PDO('mysql:host=localhost;dbname=rs;charset=utf8', 'root', '', array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
	$req = $bdd->prepare('SELECT COUNT(id_invitation) FROM amis  WHERE pseudo_exp = :pseudo_exp, pseudo_dest = :pseudo_dest OR pseudo_exp = :pseudo_exp AND pseudo_dest = :pseudo_dest');
		$req->execute(array(
		'pseudo_dest' => $_GET['pseudo'],
		'pseudo_exp' => $_SESSION['pseudo'],));
	while($donnees = $req->fetch())
	{
	++$count_user;
	}
	$req->closeCursor();
}
?>