Sporadic Myotonic Dystrophy Type 2 in a Japanese Patient

• Published in: Internal Medicine Vol. 62; no. 20; pp. 3027 - 3031
• Main Authors: Miyashita, Koichi, Ii, Yuichiro, Matsuyama, Hirofumi, Niwa, Atsushi, Kawana, Yosuke, Shibata, Soshi, Minami, Narihiro, Nishino, Ichizo, Tomimoto, Hidekazu
• Format: Journal Article
• Language: English
• Published: Tokyo The Japanese Society of Internal Medicine 15-10-2023; Japan Science and Technology Agency
• Subjects: Atrophy; Biopsy; Case Report; Electromyography; gene analysis; Internal medicine; muscle biopsy; Myotonia; Myotonic dystrophy; myotonic dystrophy type 2; Southern blotting
• ISSN: 0918-2918; 1349-7235
• DOI: 10.2169/internalmedicine.0425-22

We herein report a Japanese patient with myotonic dystrophy type 2 (DM2), which is rare in Japan. A 64-year-oldman had proximal muscle weakness and grip myotonia. Electromyography showed myotonic discharges, but dystrophia-myotonica protein kinase (DMPK) was negative for CTG repeats. A muscle biopsy revealed increased central nuclei, pyknotic nuclear clumps and muscle fiber atrophy, mainly in type 2 fibers, raising the possibility of DM2. The diagnosis was genetically confirmed by the abnormal CCTG repeat size in cellular nucleic acid-binding protein (CNBP) on repeat-primed polymerase chain reaction, which was estimated to be around 4,500 repeats by Southern blotting.