Amelogenesis imperfecta (AI) is a genetically determined enamel defect characterized by genetic and clinical heterogeneity . The prevalence and incidence of AI were established in the county of Västerbotten, northern Sweden, in 3-19-yr-olds born 1963-79, as were the mode of inheritance and clinical manifestation of AI. The distribution of the inorganic component in the enamel of AI teeth was studied as well as the surface morphology and other morphological details, and the findings were correlated to genetic and clinical data. AI was diagnosed in 79 children and adolescents (index cases). The prevalence in the study population was 1.4: 1 000. The mean yearly incidence 1963-79 was 1.3:1 000. The inheritance patterns for AI were established in 78 index cases from 51 families. Pedigree and segregation analyses suggested autosomal dominant (AD) inheritance in 3 3 families, autosomal recessive (AR) in six families, and X- linked recessive in two families; in ten families only sporadic cases were found. In one of the families with an AD inheritance pattern, X-linked dominant was a possible alternative. Examination of the families of the 78 index cases revealed 107 new cases of AI. The hypoplastic form was seen in 72% of all diagnosed cases and the hypomineralization form in 28% of the cases. A further classification of the clinical manifestations led to the identification of eight clinical variants. In 3 3 of the 51 families the same clinical variant was found in all affected members. In eight families affected members were assigned to different clinical variants. In three families with an X-linked inheritance pattern for AI, the clinical manifestation differed between women and men due to lyo- nization. Among the remaining five families, with an AD inheritance pattern for AI, variants clinically characterized by hypoplasia as well as variants characterized by hypomineralization were found in three families; in the other two families the clinical manifestation varied within the same main form of AI, i.e. hypoplasia or hypomineralization. Hypoplasia as well as hypomineralization were observed microradiographically in the enamel of most of the examined teeth. These findings were supported by scanning electron microscopy (SEM). Both clinically and microradiographically as well as by SEM, similar variants of AI were found as AD and AR traits and/or among the sporadic cases. In the families with AI as an X-linked trait the genetic hypothesis was confirmed by the clinical, microradiographic and scanning electron microscopic findings. / <p>S. 1-46: sammanfattning, s. 47-134: 5 uppsatser</p> / digitalisering@umu