• Simona Portaro, Alberto Cacciola, Antonino Naro, Demetrio Milardi, Rosa Morabito, Francesco Corallo, Silvia Marino, Alessia Bramanti, Emanuela Mazzon, and Rocco Salvatore Calabrò.
• IRCCS Centro Neurolesi "Bonino-Pulejo," Messina.
• Medicine (Baltimore). 2018 Jun 1; 97 (22): e10785.

RationaleMyotonia 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 ConcernsA 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.InterventionsThe patient was submitted to cognitive assessment, needle electromyography, brain and muscle MRI, and genetic analysis.OutcomesThe 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.DiagnosisRecessive myotonia congenita was diagnosed.LessonsFurther 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.

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