Myotonia is a cardinal symptom of adult-onset myotonic dystrophy type 1 (DM1). Myotonia, delayed relaxation following contraction, is most prominent in the hand and forearm muscles. Two sisters with genetically confirmed DM1 exhibited toe-extension myotonia (video on the Neurology® Web site at Neurology.org) in contrast to toe-flexion myotonia that can occur in DM1. There was a typical warm-up phenomenon. A variant phenotype of Charcot-Marie-Tooth–like polyneuropathy1 was not present. Mutations in the CLCN1 gene encoding the skeletal muscle chloride channel, in addition to abnormal splicing, can enhance myotonia in DM type 2.2 However, in our patients sequencing of the CLCN1 gene did not show mutations.
Supplementary Material
Acknowledgments
Acknowledgment: The authors thank Drs. Thornton and Moxley (University of Rochester, NY) for discussions; and Hirity Shimellis, Angela Kokkinis, and Dara Bakar for help with patient care and making of the video.
Footnotes
Supplemental data at Neurology.org
Study funding: Supported by intramural funding from the NIH.
Disclosure: The authors report no disclosures relevant to the manuscript. Go to Neurology.org for full disclosures.
References
- 1.Braida C, Stefanatos RK, Adam B, et al. Variant CCG and GGC repeats within the CTG expansion dramatically modify mutational dynamics and likely contribute toward unusual symptoms in some myotonic dystrophy type 1 patients. Hum Mol Genet 2010;19:1399–1412. [DOI] [PubMed] [Google Scholar]
- 2.Suominen T, Schoser B, Raheem O, et al. High frequency of co-segregating CLCN1 mutations among myotonic dystrophy type 2 patients from Finland and Germany. J Neurol 2008;255:1731–1736. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.