Myofibrillar Myopathy with a Novel LDB3 Variant (c.1804T>C) in a Filipino Mother–Daughter Dyad: A Case Report

Myofibrillar myopathy (MFM) is a rare inherited neuromuscular disorder characterised by progressive muscle weakness with potential cardiac and respiratory involvement. Mutations in the LDB3 gene disrupt Z-disk integrity, leading to myofibrillar disintegration and protein accumulation. Reports of LDB3-related MFM are limited, particularly in Southeast Asian populations. The authors describe a Filipino mother–daughter pair with genetically confirmed LDB3-associated MFM due to a novel variant. The proband developed progressive proximal muscle weakness beginning in childhood, while her daughter presented with proximal lower extremity weakness in early adulthood. Neither patient exhibited ophthalmoplegia or bulbar involvement. Electromyography and nerve conduction studies demonstrated a myopathic pattern with irritative potentials. Muscle biopsy of the proband revealed features consistent with MFM with multicore formation. Genetic testing identified a heterozygous LDB3 c.1804T>C variant in both individuals. Supportive and rehabilitative management was initiated with ongoing monitoring for systemic complications. This report represents the first documented association of the LDB3 c.1804T>C variant with MFM, expands the phenotypic spectrum of LDB3-related disease, and highlights the importance of integrated clinical, pathological, and genetic evaluation in familial proximal myopathy, particularly in underrepresented populations.