Dysarthria leads diagnosis in teen with Becker myotonia and CLCN1 variant

A 13-year-old boy in Iran arrived at clinicians with a complaint that is rarely the first sign of his condition: difficulty speaking. Rather than the muscle stiffness that usually defines myotonia congenita, dysarthria was his chief presenting symptom, and it prompted a diagnostic workup that ultimately revealed a genetically confirmed case of Becker-type myotonia congenita.

The case, published in BMC Neurology as a case report and literature review, is described by Saeed Razmeh and Amir Mohammad Dashti. Myotonia congenita is a rare inherited skeletal muscle channelopathy caused by pathogenic variants in the CLCN1 gene. It is typically characterized by muscle stiffness, delayed relaxation after contraction, and a so-called warm-up phenomenon, in which stiffness eases with repeated movement.

Although the clinical and genetic spectrum of CLCN1-related myotonia congenita continues to expand, the authors note that dysarthria is not a well-recognized presenting feature of the condition. That makes this patient’s route to diagnosis unusual, and it underlines the value of assessing speech difficulties in patients suspected of having the disorder.

The boy’s history included several years of progressive proximal muscle weakness, predominantly affecting the lower limbs. He also reported muscle stiffness that was most prominent after rest and improved with repeated movements, consistent with a warm-up phenomenon, and that worsened with cold exposure.

Neurological examination revealed generalized true muscle hypertrophy, particularly of the deltoid and back muscles, along with generalized myotonia involving the tongue. The presence of clinically evident tongue myotonia is notable given the patient’s speech complaint, and the report links the two observations directly.

Proximal muscle strength was reduced on testing, while sensory examination and deep tendon reflexes were normal. Electromyography demonstrated myogenic abnormalities with prominent myotonic discharges and no evidence of neuropathy, helping to localize the problem to the muscle itself rather than the nerves.

Whole-exome sequencing identified a homozygous pathogenic nonsense variant, NM_000083.3(CLCN1):c.1129 C > T (p.Arg377Ter), in exon 10 of the CLCN1 gene.

Treatment with mexiletine and a rehabilitation program including aerobic exercise, stretching, and physical therapy was initiated; the report does not describe long-term outcomes of this treatment plan.

The authors conclude that dysarthria was the chief presenting complaint in this genetically confirmed case and that it co-occurred with clinically evident tongue myotonia.

As a single case report, the findings describe one patient’s presentation and cannot establish how frequently dysarthria occurs across the wider population of people with CLCN1-related myotonia congenita. Nevertheless, the case adds to the documented clinical spectrum of the disorder and offers a concrete reminder that its manifestations may extend beyond limb stiffness.

Subject of Research: Dysarthria as a presenting feature of Becker-type myotonia congenita with a homozygous CLCN1 variant

Article Title: Beyond limb stiffness: dysarthria in a Persian patient with becker myotonia and a homozygous CLCN1 (p.Arg377Ter) variant-a case report and literature review

Article References: Razmeh, S., & Dashti, A. M. (2026). Beyond limb stiffness: dysarthria in a Persian patient with becker myotonia and a homozygous CLCN1 (p.Arg377Ter) variant-a case report and literature review. BMC Neurology. https://doi.org/10.1186/s12883-026-05593-y

Image Credits: AI Generated

DOI: 10.1186/s12883-026-05593-y

Keywords: myotonia congenita, Becker-type myotonia, CLCN1, dysarthria, case report, whole-exome sequencing, tongue myotonia, mexiletine, channelopathy, BMC Neurology, Beyond, limb