Secondary retention of permanent molars: a report of five families.

The aetiopathogenesis of secondary retention is not fully understood, but heredity is involved in at least some cases. In this study first-degree relatives of 52 patients with secondary retention of permanent molars were screened for the presence of the same phenomenon in their dentition. Familial occurrence could be shown in five families. The pedigrees are compatible with autosomal dominant inheritance. HLA phenotypes and blood groups ABO, rhesus and P1 were studied in two families. The lod scores for linkage with secondary retention were added to previously reported information. The lod score for linkage for blood group system P increased from +0.940 to +1.475 at a recombination fraction of 5 per cent. It is concluded that secondary retention of permanent molars is an aetiologically heterogeneous condition in which some cases are caused by the presence of an abnormal autosomal dominant gene.