ON THE GENETICS OF HYPODONTIA AND MICRODONTIA - SYNERGISM OR ALLELISMOF MAJOR GENES IN A FAMILY WITH 6 AFFECTED MEMBERS

Familial severe hypodontia of the permanent dentition is a rare condit ion. The genetics of this entity remains unclear and several modes of inheritance have been suggested. We report here an increase in the num ber of congenitally missing teeth after the mating of affected subject s from two unrelated Norwegian families. This condition may be the res ult of allelic mutations at a single gene locus. Alternatively, incomp letely penetrant non-allelic genes may show a synergistic effect as ex pected for a multifactorial trait with interacting gene products. This and similar kindreds may allow identification of genes involved in gr owth and differentiation of dental tissues by linkage and haplotype as sociation analysis. Brittle nails, delayed growth of the hair, and del ayed teething in the probands support the grouping of these conditions among the ectodermal dysplasias.