Bannayan syndrome: A rare genetic disease characterized by macrocephaly (enlarged head), multiple lipomas (benign fatty tumors) and hemangiomas (benign blood vessel tumors). The macrocephaly occurs without enlargement of the cerebral ventricles. There is mild neurological impairment and postnatal growth retardation.
Less frequent features associated with the syndrome may include down-slanting palpebral fissures (eye slits), high-arched palate, joint hyperextensibility, pectus excavatum (caved-in chest), strabismus, amblyopia, seizures, and mental retardation.
Inheritance of the syndrome is as an autosomal dominant trait. An affected parent has a 50:50 chance of transmitting the Bannayan gene to each of their children. The gene is on chromosome 10q23.3 and the mutation is now known to involve the phosphatase and tensin homolog gene called PTEN. A different mutation in PTEN causes Cowden disease, which is a syndrome of multiple hamartomas (malformations resembling tumors composed of mature tissues), especially of the skin, mucous membranes, breast and thyroid.
The syndrome is named after the Jerusalem-born American pathologist George A. Bannayan who described a case with the disease in 1971. This may not have been the first description of the disease. In 1960 Harris D. Riley and William R. Smith had reported the same (or a remarkably similar) syndrome in a mother and 4 of her 7 offspring. The syndrome is also called "macrocephaly, multiple lipomas, and hemangiomata."