3.1. Patient population and clinical studies
Clinical, echocardiographic, genetic, cardiac, and skeletal muscle morphometric characteristics of the 12 patients are shown in . In , the comparison between group A and B patients and healthy subjects (group C) is presented.
Characteristics of the 12 study patients with FD
Comparison of clinical, echocardiographic, and morphometric data among patients with FD younger than 35 years (group A), older than 35 years (group B), and healthy controls (group C)
Patients were from 7 different families. Patients 1, 2, 7, and 9 belonged to the same family. Patients 4, 5, and 6 belonged to another family. The remaining 5 patients were from different families. Patient 8 was the only one affected by the cardiac variant of FD.
Troponin I was elevated in 5 of the 12 patients (1 from group A and 5 from group B, reference value <0.15 ng/mL), whereas creatine phosphokinase and creatine kinase MB and creatine kinase MM fraction were normal in all patients. None of them smoked, had hypercholesterolemia, or had diabetes or hypertension. Cardiac magnetic resonance confirmed the morphologic and functional data observed by echocardiography and showed late-gadolinium enhancement in none of group A patients, in 5 (62%) of 8 group B patients, and in all cases localized in the basal or basal-medium segments of the inferolateral LV wall.
In 4 patients in group A, the results of muscle clinical evaluation, skeletal muscle ultrasound (A), and electromyography were normal. In group B, clinical muscular evaluation showed mild muscle weakness and pain, and the skeletal muscle echographic findings revealed a moderate to severe muscular disarray of deltoid and quadriceps femoris (A), whereas electromyography showed mild signs of myopathy.
Fig. 1 Comparison between skeletal (left column) and cardiac (right column) muscles in a 26-year-old man with early FD (patient 2). Echo findings are normal for both skeletal (A) and cardiac (B) muscles. Histology and electron microscopy of skeletal myocytes (more ...)
Fig. 2 Comparison between skeletal (left column) and cardiac (right column) muscles in a 43-year-old man with advanced FD (patient 7). Muscle echography (A) shows disarray of the muscular structure (reduction of hyperechogenic and increase of hypoechogenic areas), (more ...)
All group B patients had LV hypertrophy, documented by basal electrocardiogram and echocardiography (; B); whereas in group A, the thickness of cardiac walls was within the upper normal limit (; B).
All nerve conduction studies in the patients with FD showed latencies, amplitudes, and conduction velocities within normal limits.
3.2. Histologic, morphometric, and ultrastructural studies
Both cardiac and muscle biopsy procedures were well tolerated in all patients, and no periprocedural complications were registered.
Skeletal myocytes from group A patients did not show the presence of glycosphingolipid vacuoles either histologically or by electron microscopy (C). Glycosphingolipid deposits were present only in the endothelial and smooth muscle cells of intramural vessels that showed normal thickness (E). Conversely, in cardiomyocytes of group A patients, histologic examination showed the presence of perinuclear vacuoles containing a material that, on frozen section, stained positively with periodic acid–Schiff stain and Sudan-Black, suggesting the accumulation of glycosphingolipids. Electron microscopy revealed that these vacuoles consisted of concentric lamellar figures in single membrane–bound vesicles (myelin bodies), diagnostic for FD (D). Intramural arteries showed endothelial and smooth muscle cell glycosphingolipid infiltration without lumen narrowing (F).
Skeletal myocytes from group B patients showed the presence of glycosphingolipid vacuoles localized in the subsarcolemmal region, often in the perinuclear area, consisting of typical myelin bodies (C). Myocyte diameter was slightly and not significantly increased compared with healthy controls, and glycosphingolipid vacuoles occupied, on average, less than 20% of the cell area (). Muscle fibrosis was increased. Lumen narrowing of muscle arterioles with glycosphingolipid deposits either in endothelial and smooth muscle cells or in perivascular areas of fibrofatty replacement were also detected (E). Cardiomyocytes were bigger, and the percentage of the cell area occupied by glycosphingolipids was wider compared with group A (; D). Moreover, morphometric analysis showed an increase in interstitial and replacement fibrosis in group B compared with group A and healthy controls (). Most (>50%) of the intramyocardial arteries from patients with FD in group B showed lumen narrowing with wall thickening due to hypertrophy and proliferation of smooth muscle cells, both engulfed by glycosphingolipids, and due to increased fibrosis of the medial and intimal layer (F). Myocardial replacement fibrosis surrounding severely narrowed intramural coronary arteries was often present.
Typically, in the female patient, the cardiac and the muscle involvement showed a patchy distribution because of the pattern of inactivation of the X chromosome