Autosomal Dominant Missense DAG1 Variant Linked to Mild–Moderate LGMD R16

Figures

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  Figure 1. Pedigree. Family tree highlighting affected individuals: Patient I.1—father; Patient II.1—eldest son; Patient II.2—middle son; and Patient II.3—youngest son.

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  Figure 2. Myopathology. Patient II.1: (A) Hematoxylin and eosin‐stained sections from the left gastrocnemius biopsy at 4 years and 9 months of age showed several well‐populated fascicles comprising predominantly longitudinally sectioned myofibers. There was a single prominent focus of inflammation centered on the perimysium (circle) with a mild increase in perimysial fat. (B) The inflammatory infiltrate was rich in eosinophils and diffusely infiltrated the perimysial connective tissue and (C) surrounding necrotic myofibers. Patient II.2: (D) Hematoxylin and eosin‐stained sections from the left quadriceps biopsy taken at 5 years and 2 months of age showed compact, well‐populated myofascicles. Few fibers (< 1%) showed internal (single, central) nuclei and a rare regenerating fiber expressing embryonic/developmental myosin (inset). Patient I.1: (E) Hematoxylin and eosin‐stained sections showing fiber size diameter variation (yellow dotted lines) and multiple nuclear internalizations (black arrow). (F) CD56 positivity showing regenerating muscle fibers (0.55% of total fibers). (G) Slow myosin staining showing fiber size diameter variation and Type 1 fiber atrophy. Note: Patient II.1: no frozen…

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  Figure 3. (A) Western blot. Patient I.1: Western blot analysis showing reduced alpha‐dystroglycan expression in Patient I.1 and Patient II.1 compared to a healthy control. Alpha‐dystroglycan expression is absent in DAG1 control (biallelic variants). (B) Atomic force microscopy (AFM)–based mechanical characterization of DAG1‐deficient myoblasts. Left panel: bar plot showing the mean elastic modulus (±SD) of control and Patient I.1‐derived myoblasts (n = 7 per group; Mann–Whitney U test, p = 0.0006). Patient I.1 myoblasts show a markedly reduced elastic modulus compared to controls (4.5 ± 1.6 vs. 29.3 ± 17.6 kPa) ***p < 0.001. Right panels: representative AFM elasticity maps overlaid on phase‐contrast images of a control myoblast (left) and a Patient I.1‐derived myoblast (right), illustrating the approximately 85% decrease in elastic modulus. Color scale indicates elastic modulus values from 0 to 60 kPa. Scale bar: 20 μm.