MONDO_0011500 (Becker nevus syndrome) is characterized by the presence of a Becker nevus in association with underdevelopment (hypoplasia) of the breast or other skin-related, muscular, or skeletal defects, all of which usually involve the same side of the bodyas the nevus (ipsilateral). Specific signs and symptoms in addition to the nevus may include ipsilateral breast hypoplasia; skeletal abnormalities such ashypoplasia of the shoulder girdle, scoliosis, fused ribs, and ipsilateral shortness of the arm; and several other features. Thecondition is thought to be sporadic (occurring in individuals with no history of the condition in the family). Treatment varies depending upon the specific symptoms present and the extent of the condition in the affected individual. Also known as: pigmentary hairy epidermal nevus.