Primary lymphedema may be congenital or arise sporadically. Multiple syndromes are associated with primary lymphedema, including Turner syndrome, Milroy's disease, and Klippel-Trenaunay-Weber syndrome. It is generally thought to occur as a result of absent or malformed lymph nodes and/or lymphatic channels. Lymphedema may be present at birth, develop at the onset of puberty (praecox), or not become apparent for many years into adulthood (tarda). In men, lower-limb primary lymphedema is most common, occurring in one or both legs. Some cases of lymphedema may be associated with other vascular abnormalities.