A multi-center study published in the European Journal of Neurology (2025) has identified novel mutations in exon 363 of the titin (TTN) gene, expanding our understanding of recessive muscle disorders. Titin is the human body’s largest protein and is vital for structural and mechanical muscle stability.

By examining six patients across five unrelated families, researchers uncovered two distinct clinical outcomes linked to mutations in this specific M-band region:

• Eastern European Founder Mutation: The novel truncating variant c.107578C>T was found in four unrelated patients. Paired with a second pathogenic variant, it causes a slowly progressive, young-adult onset distal myopathy. Patients experience lower limb weakness and highly asymmetric muscle wasting, notably without cardiac or respiratory complications.

• Severe Congenital Phenotype: Conversely, a Belgian family carrying a novel frameshift deletion (c.107430delA) alongside an exon 208 mutation presented with a much more severe, early-onset progressive myopathy. This phenotype features severe joint contractures, early loss of ambulation, and restrictive lung disease.

The study concludes that while exon 363 mutations consistently cause titinopathies, the ultimate severity of the disease is dictated by the exact location and splicing behavior (“exon usage”) of the patient’s second mutated allele.