Familial aquagenic urticaria associated with familial lactose intolerance.

Aquagenic urticaria is a rare disorder characterized by the occurrence of pruritus and wheals after temporary contact with water. The familial occurrence of aquagenic urticaria over 3 generations is reported here in association with familial lactose intolerance, a condition in which the enzyme lactase encoded on chromosome 2, is deficient. In two patients, a young man and his mother, we verified the appearance of pruritic hives 5 to 10 minutes after contact with water of any temperature. Other types of physical urticaria were absent, and mastocytosis was excluded by extensive laboratory investigations; lactose intolerance was confirmed in both patients by H(2)-exhalation test. In these patients the clinical symptoms did not respond to antihistamines or UV-radiation therapy. Four other members of the family had wheals from water contact, two of whom had lactose intolerance. Two other members had lactose intolerance only. Although the association of aquagenic urticaria with lactose intolerance may be coincidental, attention is drawn to the fact that the 2 conditions, known to be familial, may coexist in the same family, possibly based on an association of gene loci.