The use of genetic linkage in counselling families with dystrophia myotonica.

The linkage between the secretor locus (Se) and the locus for the dystrophia myotonica gene (Dm) has been studied in eight families. It was hoped that this linkage would be of use for detecting carriers of the Dm gene prior to the onset of clinical signs. It proved to be of help in four out of the eight families, though for only a proportion of the individuals at risk. In one family prenatal diagnosis would have been possible for the mother of the proband, but she elected to be sterilised. In a ninth family in which the diagnosis is not yet established, prenatal diagnosis would be feasible should the proband prove to have myotonic dystrophy. Cases of infantile DM occurred in four of the eight families. In all instances, the gene was inherited from the mother. The incidence of miscarriage and neonatal death was six times as high in the families of DM sufferers as in the families of their normal siblings.