Sa'id bin al-Musayyib (may Allah have mercy on him) said that Sayyiduna Umar (may Allah be pleased with him) used to say: When a man marries a woman and she is insane, or has leprosy, or vitiligo, or qarn (an obstruction of the private part), then if he has consummated the marriage with her, she is entitled to the mahr because he touched her, and he may reclaim it from her guardian.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13773