Research ArticleGene Therapy

Plasticity of the human visual system after retinal gene therapy in patients with Leber’s congenital amaurosis

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Science Translational Medicine  15 Jul 2015:
Vol. 7, Issue 296, pp. 296ra110
DOI: 10.1126/scitranslmed.aaa8791
  • Fig. 1. Voxel-based analyses of diffusion maps comparing LCA2 patients with sighted controls.

    (A) Voxel-based analyses of LCA2 patients versus demographically matched normal sighted controls are shown for three diffusion parameters: fractional anisotropy, radial diffusivity, and mean diffusivity. Voxel-based analyses are superimposed onto the color fractional anisotropy population-based atlas constructed from all study participants (n = 21). Images of color fractional anisotropy are presented in the radiological convention (left brain is depicted on the right). In the first column, the voxel-based analyses for fractional anisotropy (revealed as yellow areas; white arrow on sagittal image, second row) showed decreased fractional anisotropy for greater than 100 contiguous voxels, which is significant after correction for multiple comparisons [false discovery rate (FDR), q < 0.05]. Axial images (top row, first column) show larger clusters with reduced fractional anisotropy in the left V1 (3272 voxels) as compared to the right V1 (2301 voxels). Sagittal images (second row, first column) are presented to demonstrate that the reduced fractional anisotropy clusters within the visual cortex are primarily located in and around the calcarine fissure (white arrow), which is also known as the primary visual area (BA-17 and BA-18). In the second column, results from voxel-based analyses for increased radial diffusivity are shown (at the same statistical threshold for fractional anisotropy) in blue clusters superimposed onto the color fractional anisotropy atlas. Similar to fractional anisotropy, the radial diffusivity clusters are larger in the left occipital cortex and primarily located in V1. In the third column, voxel-based analyses for increased mean diffusivity are also shown in blue clusters at the same statistical threshold for fractional anisotropy and radial diffusivity. The increase in mean diffusivity is not as widespread as the radial diffusivity and fractional anisotropy. This may be because no changes in axial diffusivity were detected. (B) Reduced fractional anisotropy clusters (at the same statistical threshold) in the posterior corpus callosum (corpus callosum is marked with yellow arrows) where the left and right occipital fibers that connect the two visual cortices cross. No changes in other diffusion indices were detected for the corpus callosum cluster.

  • Fig. 2. Spearman correlations for occipital fractional anisotropy with age in LCA2 patients and sighted controls.

    Shown are Spearman correlation analyses for white matter microstructural abnormalities within the right and left occipital cortex and posterior corpus callosum (CC) with age for LCA2 patients and sighted controls. LCA2 patients demonstrated similar correlations to those for sighted controls for the right occipital fractional anisotropy (FA), but the left occipital fractional anisotropy negatively correlated with age, thus demonstrating a continuous decline of the microstructural white matter in the left primary visual area for these patients. However, the posterior corpus callosum fractional anisotropy correlations with age were noticeably different for LCA2 patients compared to sighted controls. The absence of positive correlations for fractional anisotropy and patients’ age in the splenium of the corpus callosum for LCA2 patients may be due to the progressive nature of the disease, signifying the decline in communication between the two visual cortices over time and the reduction in the number of fibers crossing the splenium, which connects the left and right occipital cortices and enables binocular vision.

  • Fig. 3. Spearman correlations for the left and right occipital fractional anisotropy and time since gene therapy.

    The left and right occipital FA correlated with the number of years after gene therapy for LCA2 patients treated in their right eye at the time of the MRI scan. Results show significant negative correlations (R = −0.64, P < 0.05) for the left occipital fractional anisotropy and a trend (but not significant) toward a positive correlation (R = 0.43, P < 0.14) for the right occipital fractional anisotropy and time since gene therapy. There was a significant difference between the left and right occipital fractional anisotropy with respect to correlation with time since gene therapy (P < 0.003, Steiger’s test for dependent correlations) (33).

  • Fig. 4. Spearman correlations for occipital fractional anisotropy and the amplitude and frequency of nystagmus in LCA2 patients.

    Correlations for the left and right occipital FA and the frequency and amplitude of nystagmus for the left and right eye of LCA2 patients are shown. Nystagmus characteristics for either the right or the left eye did not correlate with the integrity of white matter microstructure within the right occipital cortex. However, there did exist significant correlations between the fractional anisotropy of the left visual cortex and nystagmus characteristics for both the left and right eye of LCA2 patients. Data are shown for 7 LCA2 patients treated in the right eye (9 of 10), with nystagmus information missing for 2 patients.

  • Fig. 5. DTI fiber tractography.

    (A) Using DTIStudio tractography software and a population-specific template, major fiber tracts connecting the occipital cortex to the rest of the brain such as the inferior fronto-occipital fibers, inferior longitudinal fasciculus, occipito-callosal, and geniculostriate fibers, as well as chiasm tracts, were extracted bilaterally. Subsequent to extractions, fiber bundles were superimposed on the color fractional anisotropy template image. The template image is shown in radiological convention (right brain side is shown on the left). Following Dougherty et al. (20), the occipito-callosal fibers were extracted by placing three regions of interest in the upper, middle, and lower areas of the inferior portion of the splenium to extract tracts that ended in dorsal V3 visual areas (blue), dorsal and ventral V1 and V2 areas (yellow), and ventral V3 and V4 areas (red). In addition to vision-related tracts, bilateral corticospinal tracts were extracted as nonvision control fibers. Tractography analyses of all of these tracts showed no difference between the LCA2 patients and sighted controls except for the geniculostriate fibers. As shown in Table 4, the averaged fractional anisotropy along the right geniculostriate fibers for the LCA2 patients did not differ from the control group (P = 0.389). However, tractography results showed significantly decreased fractional anisotropy along the left geniculostriate fibers (P = 0.0045). (B) Laterality indices (R-L) for the average fractional anisotropy along the left and right geniculostriate fibers for LCA2 patients and sighted controls were evaluated. The laterality index used was: (right geniculostriate average fractional anisotropy − left geniculostriate average fractional anisotropy)/(right geniculostriate average fractional anisotropy + left geniculostriate average fractional anisotropy). LCA2 patients showed much higher average fractional anisotropy values for the right geniculostriate fibers, and their laterality index (red bar) significantly (P < 0.04) differed from matched sighted controls (blue bar).

  • Fig. 6. Group-averaged fMRI results.

    (A and B) Group-averaged fMRI results of the right eye in response to high-contrast checkerboard stimuli (19) for sighted controls and LCA2 patients are depicted in (A) and (B), respectively. Cortical activations are presented on the brain atlas, which is shown in the neurological convention (left cortex depicted on the left). A symmetrical distribution of activation in both hemispheres for sighted controls as opposed to a clearly asymmetric activation distribution for LCA2 patients is shown. (C) The cortical activation laterality index (right total visual cortex activation volume − left visual cortex activation volume)/(right total visual cortex activation volume + left total visual cortex activation volume) is significantly larger (P < 0.003) for LCA2 patients compared to sighted controls.

  • Table 1. LCA2 patient demographics.
    DemographicsSighted controlsLCA2 patientsStatistics
    n1110
    Male86Fisher’s exact = 0.93
    Average age (years)24.37 (11.77)23.89 (12.32)T test > 0.83
    Age range (years)9.50–46.249.08–44.75
    Right-handed119Fisher’s exact = 0.48
    Average time between gene therapy and imaging (years)N/A2.09 (1.11)
  • Table 2. Cluster size and locations for diffusion results.

    Size and center of mass coordinates of the fractional anisotropy, mean diffusivity, and radial diffusivity for clusters extracted from voxel-based analyses of diffusion maps in the coordinate system of the MNI template.

    Cluster locationsMNI coordinatesCluster size (number of voxels)
    Fractional anisotropyxyz
    Left visual cortex (BA-18)−6−103−51824
    Right visual cortex (BA-17)19−8051580
    Left visual cortex (BA-17)−3−8811448
    Right visual cortex (BA-18)24−102−2378
    Right visual cortex (BA-19)43−80−2343
    Splenium of corpus callosum7−3412100
    Radial diffusivity
    Left visual cortex (BA-17)−12−81131495
    Right visual cortex (BA-18)7−81−1813
    Right visual cortex (BA-17)10−797136
    Left visual cortex (BA-17)−2−827100
    Mean diffusivity
    Right visual cortex (BA-19)20102−3601
    Left visual cortex (BA-17)−6−943540
    Right visual cortex (BA-17)11−726138
    Left visual cortex (BA-17)−2−8012120
    Left visual cortex (BA-19)−32−8617118
  • Table 3. Quantification of diffusion results.

    Average values for the fractional anisotropy, radial diffusivity, and mean diffusivity for the significant clusters listed in Table 2. These clusters were identified from the voxel-based analyses of diffusion maps of the LCA2 patients and sighted controls registered to the MNI template.

    Cluster locationLCA2 patientsSighted controls
    Average fractional anisotropy (SD)Average fractional anisotropy (SD)
    Right occipital0.202 (0.018)0.260 (0.022)
    Left occipital0.199 (0.024)0.252 (0.025)
    Splenium0.660 (0.034)0.711 (0.028)
    Average radial diffusivity (SD) (106 s/mm2)Average radial diffusivity (SD) (10−6 s/mm2)
    Right occipital743.0 (38.6)679.5 (27.2)
    Left occipital822.0 (48.8)730.9 (43.1)
    Average mean diffusivity (SD) (10−6 s/mm2)Average mean diffusivity (SD) (10−6 s/mm2)
    Right occipital816.0 (39.5)757.3 (36.4)
    Left occipital860.0 (47.8)783.0 (42.3)
  • Table 4. Fiber tractography results.

    Statistical comparison of average fractional anisotropy measurements for the right and left geniculostriate fibers for LCA2 patients and sighted controls.

    Average fractional anisotropyGroupsMeanSDP
    Right geniculostriateSighted controls0.4170.0360.389
    LCA2 patients0.4130.019
    Left geniculostriateSighted controls0.3970.0410.0045
    LCA2 patients0.3460.045
  • Table 5. Comparison of cortical activation in LCA2 patients and sighted controls.

    Statistical comparison of the total volume of cortical activation distributed within the right and left visual cortices between LCA2 patients and sighted controls resulting from the stimulation of the subjects’ right eye only.

    Cortical activationGroupsMean (mm3)SD (mm3)P
    Right occipital lobeSighted controls29,41514,6820.32
    LCA2 patients22,12913,254
    Left occipital lobeSighted controls30,14114,6720.05
    LCA2 patients15,14313,348

Supplementary Materials

  • Supplementary Material for:

    Plasticity of the human visual system after retinal gene therapy in patients with Leber's congenital amaurosis

    Manzar Ashtari,* Hui Zhang, Philip A. Cook, Laura L. Cyckowski, Kenneth S. Shindler, Kathleen A. Marshall, Puya Aravand, Arastoo Vossough, James C. Gee, Albert M. Maguire, Chris I. Baker, Jean Bennett

    *Corresponding author. E-mail: ashtari{at}chop.edu

    Published 15 July 2015, Sci. Transl. Med. 7, 296ra110 (2015)
    DOI: 10.1126/scitranslmed.aaa8791

    This PDF file includes:

    • Materials and Methods
    • Table S1. Demographic summary for LCA2 patients including clinical data for visual acuity and visual fields at the time of MRI.
    • References (5156)

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