Background: Congenital myotonic dystrophy (CDM) is the most severe form of myotonic dystrophy type 1, resulting in both cognitive and motor development delays. Motor function is a key aspect of CDM and could be incorporated as an important aspect of future trial endpoints, however, understanding of CDM natural history is limited. We therefore assessed motor function in affected children aged 0 to 15 yrs.
Methods: CDM was confirmed with genetic testing; healthy control (HC) children were also enrolled. All parents/children provided written informed consent/assent. Motor milestones were obtained via parent report. The Bayley gross and fine motor scales were administered at baseline, 1 year and two years. Analysis between CDM and HC was performed using Student’s t test.
Results: The mean age at enrollment was 7.5 yrs. for CDM (N=39) and 9.0 yrs. for HC (N=26). Motor milestones in CDM were delayed compared to HC: crawling (1.4 vs. 0.59 yrs., p-value <0.0001), speaking (2.1 yrs. vs. 1.0 yrs., p-value <0.0001), walking (2.0 yrs. vs. 1.0 yrs., p<0.0001) toileting (4.6 yrs vs. 2.7 yrs., p=0.002), and reading (5.5yrs vs 4.7 yrs., p=0.01). Among subjects who completed the Bayley, CDM (n=10) had lower raw score on Bayley gross (36.6 vs 59.3, p-value= 0.05) and fine motor (31.2 vs 49.6, p-value=0.04) scales compared to HC (n=5). Likewise, in the children under 3.5 yrs., CDM patients (n=4) showed consistent trends of lower raw score on Bayley gross motor (18 vs 49.8, p-value=0.04) and Bayley fine motor (13.6 vs 37.3, p-value=0.03) scales compared to HC (n=2).
Conclusions: CDM patients have severe motor function delays compared to typically developing children based on data from parent milestone recall and Bayley motor scales. However, there is heterogeneity among CDM patients and additional affected children aged 0-4 yrs. are being recruited to adequately define the natural history during development.