PHP MYSQL syntax error

I'm trying to pull member info from a database and get this error:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' FROM users WHERE user_id = 0' at line 8 That user does not exist.

I am not sure what to change as I am new to PHP.

My code with the error is:

<?php

function fetch_users() {

    $result = mysql_query('SELECT `user_id` AS `id`, `user_username` AS `username` FROM `users`');

    $users = array();

    while (($row = mysql_fetch_assoc($result)) !== false) {
        $users[] = $row;
    }

    return $users;
}

function fetch_user_info($uid) {
    $uid = (int)$uid;

    $sql = "SELECT 
                `user_username` AS `username`,
                `user_firstname` AS `firstname`,
                `user_lastname` AS `lastname`,
                `user_email` AS `email`,
                `user_about` AS `about`,
                `user_location` AS `location`,
                `user_gender` AS `gender`'
            FROM `users`
            WHERE `user_id` = {$uid}";

    $result = mysql_query($sql);            

    /*Echo mysql_error();*/


    return mysql_fetch_assoc($result);          
} ?>