Neurodegeneration of White and Gray Matter in the Hippocampus with FXTAS

Abstract

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder that affects older premutation carriers (55-200 CGG repeats) of the fragile X gene. Despite the high prevalence of the FXTAS disorder, neuropathology studies of individuals affected by FXTAS are limited. We performed hematoxylin and eosin (H&E) staining in the hippocampus of 26 FXTAS cases and analyzed the tissue microscopically. The major neuropathological characteristics were white matter disease, intranuclear inclusions in neurons and astrocytes, and neuron loss. Astrocytes contained more and larger inclusions than neurons. There was a negative correlation between age of death and CGG repeat length in cases over the age of 60. The number of astroglial inclusions (CA3 and dentate gyrus) and the number of CA3 neuronal inclusions increased with elevated CGG repeat length. In the two cases with a CGG repeat size less than 65, FXTAS intranuclear inclusions were not present in the hippocampus, while in the two cases with less than 70 (65-70) CGG repeat expansion, neurons and astrocytes with inclusions were occasionally identified in the CA1 sub-region. These findings add hippocampus neuropathology to the previously reported changes in other areas of the brain in FXTAS patients, with implications for understanding FXTAS pathogenesis.

Keywords: FXTAS; hippocampus; pathology.

Figure 1

(A) Hippocampus of a control case without significant pathological findings. Hippocampal subfields are marked: the cornu ammonis (CA) and the dentate gyrus (DG). The squares delineate the two areas of CA (CA1 and 3) and two of DG (DG1 and 2) analyzed in this study (H&E, ×360). (B–J) Hippocampus neuropathological characteristics of human FXTAS in H&E. (B) The FXTAS hippocampal white matter depicts gradations of severe spongiosis, indicative of vacuolar degeneration and parenchymal pallor in subcortical white (H&E, ×36). (C) Higher power of vacuolar changes (arrowheads) (H&E, ×360). (D) The FXTAS hippocampus presents disseminated white matter gliosis (arrowheads) and PVC (arrows). (E) Necrotic neurons within the granular layer of a hippocampus with FXTAS, shrunken eosinophilic cytoplasm, and pyknotic or karyorrhectic nuclei (arrowheads). (F) In FXTAS, the hippocampus reveals severe neuron loss and spongiosis (D–F; H&E, ×360). (G) Higher power of subfigure (F) (H&E, ×720). (H) Eosinophilic intranuclear inclusions in pyramidal cells (arrows) and an astroglial cell (arrowhead) in the FXTAS hippocampus. (I) There are two types of intranuclear inclusions in CA3 pyramidal cells. Inclusions with a white halo that are more eosinophilic (thick arrowheads) and some inclusions without vacuole (thin arrowhead). An inclusion-bearing astrocyte in the same area (arrow). (J) Intranuclear inclusions in granule cells of the dentate gyrus of case 11 (arrowheads) (H–J; H&E, ×720).

Figure 2

Vascular changes of the hippocampus in FXTAS include (A) thickening and hyalinized walls (arrow). (B) perivascular clearing (arrowheads). (C) Perivascular cuffing (PVC) (arrowheads). (D) Hypertension (arrow) and (D,E) microhemorrhages (arrowheads) (H&E, ×360).

Figure 3

Cells (neurons and astrocytes) and inclusion number analysis of the FXTAS hippocampus. (A) The number of pyramidal neurons in both CA1 and CA3 areas of FXTAS cases (58.34 ± 27.37 and 47.4 ± 16.28, respectively) significantly declined by 34% and 11.9% compared to the control (92.87 ± 42.34 and 59.3 ± 15.2) (p < 0.05). (B) The number of astrocytic inclusions in DG (25.49%) was higher than in CA1 or CA3 (8.78% and 11.02%, respectively). In the CA area, the number of astrocytic inclusions was higher than neuronal inclusions, and also, the number of inclusions (both neuronal and astrocytic) in the CA3 area was higher than in CA1 (the percentage of neurons and astrocytes with inclusions for CA1 was 5.47% and 8.78%, and for CA3 it was 8.85% and 11.02%, respectively).