DNA confirmation of congenital myotonic dystrophy in non-immune hydrops fetalis.

We report on the prenatal diagnosis of congenital myotonic dystrophy in a case of non-immune hydrops fetalis. DNA analysis of amniocytes revealed expansion of the trinucleotide (CTG) repeat within the myotonin PK gene, associated with myotonic dystrophy. The fetus was found to have approximately 1730 copies, while the normal population has between 5 and 27 copies, and minimally affected individuals have at least 50 copies.