Tropomyosin 3 variant causing adult onset distal myopathy

Background: We report a patient with a novel c.737C>T variant (p.Ser246Leu) of the TPM3 gene presenting with adult-onset distal myopathy. Case Presentation: A 35-year-old Chinese male patient presented with a history of progressive finger weakness. Physical examination revealed differential finger extension weakness, together with predominant finger abduction, elbow flexion, ankle dorsiflexion and toe extension weakness. Muscle MRI showed disproportionate fatty infiltration of the glutei, sartorius and extensor digitorum longus muscles without significant wasting. Muscle biopsy and ultrastructural examination showed a non-specific myopathic pattern without nemaline or cap inclusions. Genetic sequencing revealed a novel heterozygous p.Ser246Leu variant (c.737C>T) of the TPM3 gene which is predicted to be pathogenic. This variant is located in the area of the TPM3 gene where the protein product interacts with actin at position Asp25 of actin. Mutations of TPM3 in these loci have been shown to alter the sensitivity of thin filaments to the influx of calcium ions. Conclusion: This report further expands the phenotypic spectrum associated with TPM3 mutations and adds to the repertoire of genetic disorders reported to cause adult-onset inherited distal myopathy.