Genetic counselling for myotonic dystrophy: a comparison of lens examination and DNA linkage studies.

Genetic counselling in presymptomatic individuals with a family history of myotonic dystrophy (DM) is problematic. A genetic test to identify the presymptomatic carrier of the gene for DM would therefore be advantageous. We report studies comparing ophthalmic examination with a genetic test based on DNA linkage studies in nine DM families. The genetic test involved the use of five probes from four loci linked to the DM locus. Some discrepancies between ophthalmic and genetic tests were observed. Genetic counselling following prediction of genetic status was possible for 18 out of 20 patients from seven out of nine families.