Hypodontia, the congenital absence of one or a few permanent teeth, is one of the most frequent alterations of the human dentition, Although hypodontia does not represent a public health problem, it may cause both speech and masticatory dysfunction and esthetic problems. A missense mutation in the homeodomain of MSX1 gene has been associated with hypodontia of second premolars and third molars in humans. However, another study excluded this gene as causative locus for hypodontia of incisors and premolars, To further investigate the role of the MSX1 gene in human hypodontia, we analyzed the homeobox region of the MSX1 gene in 20 individuals with different patterns of familial or isolated hypodontia, The direct sequencing of PCR products did not show any polymorphisms or mutations in the human MSX1 gene, Our results indicate that inactivation of MSX1 gene in humans must have a highly selective effect on dentition, and other genes must be involved in the cause of hypodontia in humans. Am. J. Med. Genet. 92:346-349, 2000. (C) 2000 Wiiey-Liss, Inc.925346349