Rhabdomyolysis as an Uncommon Manifestation of Anoctamin-5 Muscular Dystrophy.

Background: Anoctamin-5 (ANO5) muscular dystrophy is a rare neuromuscular disease. Muscular weakness and impaired gait may be evident at the moment of diagnosis, serving as defining characteristics of additional muscular dystrophies. Rhabdomyolysis, on the other hand, is a rare presentation Understanding this phenotype is of great importance since it can go unnoticed by physicians, leading to misdiagnosis of metabolic myopathies or delayed diagnosis. We discuss a case of recurrent rhabdomyolysis due to ANO5 muscular dystrophy.

Case report: A 34-year-old man was referred to our Reference Centre for Hereditary and Metabolic Diseases due to incidentally elevated creatine kinase levels of 4369 U/l (normal value: < 171 U/l) in the context of acute renal colic. He described a 10-year history of progressive myalgia induced by physical activity, particularly in the lower extremities, muscle spasms, and sporadic reddish to brown urine. Although no muscle weakness was detected upon neurological examination, bilateral calf hypertrophy was noted. A comprehensive laboratory analysis was conducted to exclude acquired causes of rhabdomyolysis, including electrolyte abnormalities, endocrine disruptions, and autoimmune myopathies. Considering the high suspicion of an inherited aetiology, we proceeded with next-generation sequencing of rhabdomyolysis-related genes. Genetic testing revealed a c.1180+6t>Cp homozygous mutation in ANO5 gene, which confirmed anoctamin-5 muscular dystrophy.

Conclusions: ANO5 muscular dystrophy is a rare cause of inherited rhabdomyolysis. Understanding this phenotype is crucial for accurate and timely diagnosis. Currently, there is no specific treatment for this condition, but management should include avoiding heavy muscle training and use of statins.

Learning points: Anoctamin-5 (ANO5) muscular dystrophy is a rare neuromuscular disease originated by homozygous mutations in ANO5, a gene encoding a protein with the same name located on chromosome 11. ANO5 is a calcium-activated chloride channel that is highly expressed in heart and skeletal muscle. It is a rare cause of inherited rhabdomyolysis. Understanding this phenotype is crucial for accurate and timely diagnosis.We must emphasize how meticulous medical history taking along with a high index of suspicion are essential to diagnose this disease.Currently, there is no specific treatment for this condition, but management should include avoiding heavy muscle training and use of statins.