Review Article

Molecular Genetics and Genetic Testing in Myotonic Dystrophy Type 1

Table 1

The main indications for genetic testing in DM1 given by The International Myotonic Dystrophy Consortium (IDMC) [38], complemented with the suggested indications for preimplantation genetic diagnosis [116].

Genetic testingIndication for testing

Confirmatory or symptomatic(i) To confirm the clinical diagnosis: the gene test will increase the physician’s confidence in diagnosing a patient with typical symptoms.
(ii) To clarify an uncertain/differential clinical diagnosis: the gene test will be useful for individuals in whom DM1 is part of a wider differential diagnosis.

Asymptomatic or preclinical(i) To determine which progenitor has DM1 mutation, and this information is important in genetic counseling and carrier testing to the relevant side of the family.
(ii) To modify a priori risk of inheriting the DM1 allele.
(iii) To test asymptomatic parent who has 50% risk for DM1 and requires prenatal testing.*

Prenatal testing(i) If a parent has already been diagnosed with DM1, genetic test can be used to assess fetal risk.
(ii) If a parent is at 50% risk and asymptomatic, the best approach is a two-step process by which at-risk parent is tested first, and prenatal diagnosis is done subsequently (if still necessary).
(iii) Prenatal diagnosis should not be considered if parents would have the child regardless the test result.

Preimplantation testing(i) Alternative for prenatal testing.
(ii) Couples with concomitant infertility.
(iii) Couples unwilling to undergo termination of pregnancy.

In addition to IDMC indications.