Though the phenotype of hypodontia in Family B was milder than Family A, the hypodontia in Family B was inherited as the same X-linked dominant trait as in Family A. Therefore we also selected EDA as a candidate gene in Family B and directly examined Family B for possible mutations in EDA. After mutation screening of eight exons of EDA gene in Family B, a c.1013C>T transition mutation of EDA gene was observed (Fig. 5). The gene discussed is EDA; the disease is tooth agenesis.