Tentar:
$getquery = "(SELECT *
FROM highscore
WHERE score >= '$score'
ORDER BY score ASC
LIMIT 6)
UNION ALL -- guaranteed to be beneficial in this case as Johan commented
(SELECT *
FROM highscore
WHERE score < '$score'
ORDER BY score DESC
LIMIT 5)";
Consulte o comentários à minha resposta na pergunta relacionada .
Ou consulte o manual de multa .