Abu al-Sha'tha' (may Allah have mercy on him) said: It is not permissible to leave four things undisclosed in marriage and sale; if they are specified it is fine, otherwise it is not valid. Those four things are: insanity, leprosy, vitiligo and qarn.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14225