A case report of recessive myotonia congenita and early onset cognitive impairment: Is it a causal or casual link?

RATIONALE

Myotonia congenita (MC) is a non-dystrophic myotonia inherited either in dominant (Thomsen) or recessive (Becker) form. MC is due to an abnormal functioning of skeletal muscle voltage-gated chloride channel (CLCN1), but the genotype/phenotype correlation remains unclear.

PATIENT CONCERNS

A 48-year-old man, from consanguineous parents, presented with a fixed muscle weakness, muscle atrophy, and a cognitive impairment. Notably, his brother presented the same mutation but with a different phenotype, mainly involving cognitive function.

INTERVENTIONS

The patient was submitted to cognitive assessment, needle electromyography, brain and muscle MRI, and genetic analysis.

OUTCOMES

The Milan Overall Dementia Assessment showed short-term memory, verbal fluency and verbal intelligence impairment. His genetic analysis showed a recessive splice-site mutation in the CLCN1 gene (IVS19+2T>A). Muscle MRI revealed a symmetric and bilateral fat infiltration of the tensor of fascia lata, gluteus medius, and gluteus maximus muscles, associated to mild atrophy.

DIAGNOSIS

Recessive myotonia congenita was diagnosed.

LESSONS

Further studies should establish if and to which extent the CLCN1 mutation is responsible for this c MC phenotype, taking into account a gene-gene and /or a gene-environment.