Case Reports: Novel Missense Variants in the Filamin C Actin Binding Domain Cause Variable Phenotypes

Figures

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  Figure 1. Histopathological findings. Patient 1 (biceps brachii muscle; magnification: 200x): Gomori trichrome stain showing a slightly increased variability in muscle fibers diameter; no rimmed vacuoles and no sarcoplasmic or intranuclear inclusions were present (A). NADH-TR stain showing “moth-eaten” or “core-like” areas of oxidative enzyme activity reduction in both fiber types and increased subsarcolemmal activity in some type I fibers (darker blue areas) (B). Patient 2 (vastus lateralis muscle; magnification: 200x): Gomori trichrome stain showing an almost normal fiber variability pattern; no rimmed vacuoles and no inclusions were present (C). NADH-TR stain shows slightly “core-like” reduction of central oxidative enzyme activity in both fiber types (D). Patient 1 pictures showing intrinsic hand, foot, leg and thigh muscles wasting (E–H). Scale bar: 25 μm.

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  Figure 2. Electron microscopy. Representative images of patients 1 (A–D) and 2 (E–H). Patient 1: altered ultrastructural sarcomere pattern in transverse section (A). Degeneration of sarcomere structure with extended area of myofibrillar disorganization in the sarcoplasm (B,C). Also, many cytoplasmic vacuoles (C). Collection and increase of intermyofibrillar mitochondria with normal morphology (D). Patient 2: normal appearance of sarcomere pattern (E). Degeneration of sarcomere structure with extended area of myofibrillar disorganization at the sub-sarcolemma level (F). Area of myofibrillar disorganization with cytoplasmic bodies (G). Abnormal mitochondrial accumulation, some mitochondria are swollen or with altered cristae (H). Scale bar: short dash 463 nm, long dash 926 nm.

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  Figure 3. Molecular studies. (A) Pedigrees of the described families. Index patients are indicated with arrows. Black symbols indicate clinically affected subjects. Gray symbol indicates subclinical involvement. Available genotypes are reported under the corresponding subjects. [(B), top] Variants identified in the patients (sequence electropherograms) affecting conserved amino acidic residues within the actin binding domain. [(B), bottom] Diagram showing the structure of FLNC gene and the protein domains observed in the encoded protein (Filamin-c).

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  Figure 4. Muscle MRI. Patient 2 (A–D) and patient 2's father (E–H) Turbo Spin Echo (TSE) axial T1 MRI images from thigh (A–C, E–G) to leg (D,H). The patient's images show bilateral symmetric selective fatty degeneration of the distal insertion of the gluteus medius muscle [(A), red arrow], subfascial fatty degeneration of vastus lateralis and intermedius muscles [(B), red dotted arrow], with a relative sparing of rectus femoris, involved only at the distal insertion [(C), red arrow]; fatty degeneration and wasting of semimembranosus and long head of biceps femoris muscle [(C), black arrows] with relative preservation of gracilis, sartorious and semitendinosus muscles [(C), red dotted arrows]. In the lower leg, there is a predominant fibroadipose replacement of the posterior muscles, primarily affecting the soleus and the medial gastrocnemius muscles [(D), red dotted arrows]. The same involvement pattern of selected muscle groups can also be observed in the patient's father, although it is less pronounced except at the level of the distal leg.