Parental diagnostic delay and developmental outcomes in congenital and childhood-onset myotonic dystrophy type 1

Abstract

Myotonic dystrophy type 1 (DM1) is a multisystem disorder. A diagnostic lag has been described in DM1 due to the non-muscular symptoms often underestimated by the individuals with DM1. This diagnostic delay has implications in family planning as the offspring of parents with DM1 often have the more severe congenital (CDM) or childhood-onset (ChDM) disease. Knowing the parental diagnosis before conception would allow an appropriate pre- and perinatal support for women and children.

We aimed to investigate the timing of the diagnosis of DM1 (i.e. before or after the birth of offspring with DM1) in the parents of children with CDM or ChDM referred to 13 Italian and 1 US highly specialized centres between 2010 and 2022. Also, we described the level of disease burden of children with the disorder at birth and over time.

We included 139 children; 105 were children with CDM and 34 with ChDM. Seventy parents, corresponding to the 50% of the couples in the study, were diagnosed with adult-onset DM1 because of the diagnosis of the child. On the other hand, only 12 (17%) of the 69 parents who knew they were affected decided to conduct prenatal testing.

The disease burden in children with CDM was very high with 36% being born preterm, 83% requiring NICU for more than 48 hours. Developmental milestones were delayed with 84% and 79% having ambulation and speech delay and 84% of children with the congenital form had an IQ below 70, suggesting cognitive impairment. The 34 children with ChDM did not have significant perinatal issues but almost 40% had an IQ below 70.

The diagnostic delay in DM1 affects family planning. The pre- and perinatal outcomes of the affected offspring emphasize the need for proactive counselling as parents may be reluctant to conduct prenatal testing.