Myotonic Dystrophy Type 1 (DM1): Clinical Characteristics and Disease Progression in a Large Cohort

Background: DM1 is a multisystem disorder caused by expansion of a CTG triplet repeat in the 3' non-coding region of DMPK. Neuropsychological consequences and sleep abnormalities are important associations in DM1. Objective: To describe the clinical phenotype, disease progression and characterize the sleep alterations and cognitive abnormalities in a sub-set of patients. Materials and Methods: A retrospective study on 120 genetically confirmed DM1 cases. Findings in neuropsychological assessment and multiple sleep questionnaires were compared with 14 age and sex matched healthy individuals. All 120 patients were contacted through letters/telephonic consultation/hospital visits to record their latest physical and functional disabilities. Results: The mean age at symptom onset was 23.1 +/- 11.4 years, M: F = 3.8:1, mean duration of illness = 14.3 +/- 9.5 years. Clinically 54.2% had adult onset form, juvenile = 27.5%, infantile = 10.8%, late adult onset = 7.5%. Paternal transmission occurred more frequently. The predominant initial symptoms were myotonia (37.5%), hand weakness (21.7%), lower limb weakness (23.3%) and bulbar (10%). Twenty patients completed sleep questionnaires (SQ). Abnormal scores were noted in Epworth sleepiness scale (55%); Pittsburgh sleep quality index (45%); Berlin SQ (30%); Rapid eye movement sleep Behaviour Disorder SQ (15%); Restless leg syndrome rating scale (10%). Neuropsychological assessment of 20 patients revealed frontal executive dysfunction, attention impairment and visuospatial dysfunction. Frontal lobe was most affected (72%) followed by parietal (16%) and temporal lobe (12%). Conclusions: The current study provides a comprehensive account of the clinical characteristics in Indian patients with DM1. Hypersomnolence was most commonly seen. Excessive daytime sleepiness and Sleep disordered breathing were the most common sleep related abnormality. Cognitive impairment comprised predominantly of frontal lobe dysfunction.