The body of a 34-year-old female was received through the Saint Louis University (SLU) Gift Body Program with signed informed consent. The available medical history reported FRDA diagnosis at the age of 10, congestive heart failure, type 1 diabetes mellitus, scoliosis, acid reflux, muscle spasms, atrophy of the feet, and wheelchair dependence since adolescence. The cause of death was acute respiratory failure secondary to congestive heart failure.

Magnetic resonance imaging (MRI) was performed at the SSM Health Saint Louis University Hospital as previously described [5].

Removal of the brain and heart followed the dissection procedures in Grant’s Dissector, 16th edition [6]. After their removal, the specimens were submerged in a 10% neutrally buffered formalin solution for approximately eight weeks.

The heart was sectioned transversely from the midventricular line to the apex, while the brain was sliced coronally into 10 mm sections. Regions of each specimen were removed, dehydrated, paraffin-embedded, sectioned (4 - 5 μm), and stained with hematoxylin and eosin (H & E) according to standard procedures of the Advanced Spatial Biology and Research Histology Facility (Department of Pathology, SLU School of Medicine).

Images were obtained with a Leica Leitz DMRB light microscope equipped with a DFC7000 T camera and controlled by the Neurolucida software (MBF Bioscience, Williston, VT, USA) using the 4×, 10×, 20×, and 63× objectives. Contours were manually traced in Neurolucida using the continuous tracing tool. Six representative regions of the cardiac interventricular septum were selected, and contours were drawn around cardiomyocytes with a visible nucleus. Cells extending beyond the region boundaries were excluded. The average cardiomyocyte cross-sectional area was then calculated. For the dentate nucleus, neurons with a visible nucleus were selected, and contours were manually drawn around each neuronal soma. Neuronal soma area measurements were subsequently obtained.

The postmortem genetic screening by WES was conducted by Novogene (Sacramento, CA) to a 50× depth of coverage on the Illumina HiSeq 2500 NGS platform. The respective bioinformatics analysis, including detection of genes with rare (minor allele frequency, MAF ≤ 0.01) and low-frequency (0.01 < MAF < 0.05) pathological/deleterious genetic variants and their functional annotation, was performed as previously described [7]. By virtue of detecting mutations in the DNA coding regions (exons), WES in the current study was not aimed at identifying canonical FXN GAA repeat expansions in the donor’s DNA non-coding regions (introns).

External body examination revealed cavovarus foot deformity (Figure 1(A)), while MRI demonstrated the existence of levoscoliosis and the presence of a foreign metal object (Figure 1(B)), which was identified during anatomical dissection as an implantable cardioverter-defibrillator (ICD). The latter would be consistent with ventricular tachycardia (VT) being present in the donor. Since cardiomyopathy is one of the possible underlining causes of VT, the histopathological analysis of the donor’s heart was performed. H & E-stained heart interventricular septum revealed hypertrophic cardiomyocytes with irregular contours, size variability, and large, rectangular, so-called “box-car” nuclei (Figure 2(A)). A total of 415 cardiomyocytes were counted with a mean cross-sectional area of 2304 μm² (range, 212 - 9780 μm²) vs. a normal mean of 249 μm² [8]. The putative CNS pathology underlining FRDA’s key neurological symptoms was probed by histopathological analysis of the cerebellum. H & E-stained cerebellar dentate nucleus showed predominantly small neuronal cell bodies (Figure 2(B)). A total of 754 neurons were counted in the right and left dentate nuclei, with a mean diameter of 17 μm (range, 9.4 - 29.1 μm). Only 2% of neurons exceeded 25 μm in diameter, whereas 98% were <25 μm, indicating a significant loss of large neurons. In the normal dentate nucleus, approximately 70% of neurons are large, and depletion of this population is a well-recognized pathologic feature of dentate degeneration and cerebellar disease [9][10].

Figure 1. Anatomical findings in the FRDA body donor. (A) External examination demonstrating bilateral cavovarus foot deformity. (B) Coronal MRI illustrating levoscoliosis. The yellow asterisk denotes the implantable cardioverter-defibrillator in the left upper chest.

Figure 2. Histopathological findings in the FRDA body donor. Representative H&E-stained sections used for morphometric analysis. (A) Cardiac tissue demonstrating cardiomyocyte hypertrophy, with blue tracings outlining analyzed cardiomyocytes. Enlarged nuclei with squared nuclear contours (“box-car nuclei”), a characteristic feature of cardiomyocyte hypertrophy, are indicated by black arrows. (B) Cerebellar dentate nucleus showing predominance of small neurons and loss of large neurons, consistent with dentate nucleus degeneration in Friedreich ataxia; blue tracings outline analyzed neuronal cell bodies. Scale bars = 50 µm.

Using a very stringent, five-step analytical algorithm where the last three steps included consecutive filtering of genetic variants through SIFT, PolyPhen_2-HDIV, and PROVEAN databases [7], 77 genes with rare (R) and 67 genes with low-frequency (LF) pathological/deleterious mutations were identified. Those genes were then manually grouped into 9 functional categories most relevant to the present case: Development, Neurodevelopment, Bone/Cartilage Development, Muscle Development/Function, Mitochondrial Function, Cilia Development/Function, Immunity/Inflammation, Neurological Diseases, and Cardiovascular Diseases (Table 1 and Table 2). These categories were chosen based on the FRDA diagnosis and its associated comorbidities reported in the medical history of the body donor, the most relevant physiological pathways potentially affected in the donor, as well as on the results of the respective pathological examination (see above).

Table 1. Genes with rare pathological/deleterious variants that are most relevant to the present case.

Table 2. Genes with low-frequency pathological/deleterious variants that are most relevant to the present case.