The congenital lack of one or more permanent teeth (hypodontia), is a common anomaly [Pemberton et al., 2005]. Eighty to eighty-five percent of reported cases of hypodontia involve the agenesis of just one or two teeth [Muller et al., 1970], indicating that most affected individuals have a mild form of the disorder. The tooth most commonly missing is the third molar (or wisdom tooth), which is absent in as much as 20% of the population. Tooth agenesis involving the mandibular central and lateral permanent incisors has the lowest incidence [Pemberton et al., 2005].

Hypodontia can occur in association with other developmental anomalies (syndromic) or as an isolated condition (non-syndromic). Genes associated with several syndromic conditions that present hypodontia have been identified, including the EDA gene underlying ectodermal dysplasia [Kere et al., 1996]. Three genes underlying nonsyndromic hypodontia have been identified to date: PAX9 [Stockton et al., 2000], MSX1 [Vastardis et al., 1996], and AXIN2 [Mostowska et al., 2006]. An Indian family (DEN11) segregating an apparent X-linked dominant form of hypodontia (Fig. 1A) affecting predominantly incisor teeth (Fig. 1B, C) was ascertained (Baylor College of Medicine IRB Protocol