Pfeiffer syndrome is a rare genetic disorder, characterized by the premature fusion of certain bones of the skull (craniosynostosis), which affects the shape of the head and face. The syndrome includes abnormalities of the hands and feet, such as wide and deviated thumbs and big toes. Pfeiffer syndrome is caused by mutations in the fibroblast growth factor receptors FGFR1 and FGFR2. The syndrome is grouped into three types: type 1 (classic Pfeiffer syndrome) is milder and caused by mutations in either gene; types 2 and 3 are more severe, often leading to death in infancy, caused by mutations in FGFR2. There is no cure for the syndrome. Treatment is supportive and often involves surgery in the earliest years of life to correct skull deformities and respiratory function. Most persons with Pfeiffer syndrome type 1 have a normal intelligence and life span; types 2 and 3 typically cause neurodevelopmental disorders and early death. Later in life, surgery can help in bone formation and facial construction. Pfeiffer syndrome affects about 1 in 100,000 persons. The syndrome is named after a German geneticist, Rudolf Arthur Pfeiffer (1931–2012), who described it in 1964. Many of the facial characteristics result from the premature fusion of the skull bones (craniosynostosis). The head is unable to grow normally, which leads to a high, prominent forehead (turribrachycephaly) and eyes that appear to bulge (proptosis) and are set wide (hypertelorism). In addition, there is an underdeveloped upper jaw (maxillary hypoplasia). More than half of children with Pfeiffer syndrome have hearing loss; dental problems are common. A baby with Pfeiffer syndrome may have a small, beak-shaped nose; crowded, crooked teeth; and sleep apnea, due to nasal blockage. There are three main types of Pfeiffer syndrome: type I is the mildest and most common; type II is the most severe, with neurological problems and a cloverleaf deformity; and type III is similar to type II, but without the cloverleaf deformity.