Objective To investigate the clinical and genetic characteristics of myotonic dystrophy type 1(DM1).Methods A DM1 patient and his family members admitted to the First Affiliated Hospital of Soochow University in May 2023 were examined by physical examination,EMG,muscle biopsy and genetic detection,and the family pedigree was drawn to analyze the clinical characteristics and genetic manifestations of the patients.Results There were 9 members in this family,2 of whom were suffering from DM1,and there was a phenomenon of genetic anticipation.Both patients with DM1 had typical symptoms such as myotonia and myasthenia,accompanied by involvement of multiple systems such as the central nervous system,heart,and endocrine system.The electromyogram showed characteristic myotonic potentials.Muscle biopsy of the proband showed typical myotonic dystrophy with rimmed vacuoles.Genetic detection found that their DMPK genes both had a large number of CTG trinucleotide repeat expansions.Oxcarbazepine treatment is effective.Conclusions DM1 is a genetic disease with typical symptoms of myotonia and myasthenia gravis,accompanied by involvement of central nervous system,heart,endocrine and other systems.Electromyography,muscle biopsy and gene detection can help to diagnose DM1.Rimmed vacuoles are rare in muscle pathology.Oxcarbazepine can improve the symptoms of myotonia.