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Supernumerary nipples–uropathies–Becker's nevus syndrome is a skin condition that may be associated with genitourinary tract abnormalities. Supernumerary nipples, also referred to as polythelia or accessory nipples, is a pigmented lesion of the skin that is present at birth. This pigmentation usually occurs along the milk lines, which are the precursors to breast and nipple development. Clinically, this congenital condition is generally considered benign, but some studies have suggested there may be an association with kidney diseases and cancers of the urogenital system. Becker's nevus typically presents as a unilateral, non-cancerous patch of skin that is hyperpigmented and has excessive hair, often occurring on the chest, shoulder. and back. The term "Becker's nevus syndrome" is used to describe Becker's nevus occurring along with other skin, musculoskeletal, or other tissue abnormalities such as supernumerary nipples. There are some reports documenting an association between supernumerary nipples, Becker's nevus syndrome, and urinary tract abnormalities, although with conflicting results. This association has been dubbed "SNUB syndrome".
SNUB syndrome may be considered part of the broader category of epidermal nevus syndromes, which is described as the presence of any type of epidermal nevus together with other developmental abnormalities in the skin, eyes, brain, heart, skeletal system, or urinary or genital systems. Genitourinary tumors, such as kidney or bladder cancers, have been reported to occur earlier in life and more often in individuals with epidermal nevus syndrome. However, there have not been sufficient controlled clinical studies to confirm the association between epidermal nevi and kidney and urinary tract abnormalities. On the other hand, studies on supernumerary nipples have found an association between supernumerary nipples between kidney and urinary tract abnormalities. While the prevalence of urinary tract abnormalities is about 1-2% in the general population, the frequency can rise to about 14.5% in individuals with supernumerary nipples.