Genetic Reasons for Phenotypic Diversity in Neuronal Ceroid Lipofuscinoses and High-Resolution Imaging as a Marker of Retinal Disease

Abstract

Purpose: To describe the clinical characteristics, natural history, genetic landscape, and phenotypic spectrum of neuronal ceroid lipofuscinosis (NCL)-associated retinal disease.

Design: Multicenter retrospective cohort study complemented by a cross-sectional examination.

Subjects: Twelve pediatric subjects with biallelic variants in 5 NCL-causing genes (CLN3 lysosomal/endosomal transmembrane protein [CLN3], CLN6 transmembrane ER protein [CLN6], Major facilitator superfamily domain containing 8 [MFSD8], Palmitoyl-protein thioesterase 1 ([PPT1], and tripeptidyl peptidase 1 [TPP1]).

Methods: Review of clinical notes, retinal imaging, electroretinography (ERG), and molecular genetic testing. Two subjects underwent a cross-sectional examination comprising adaptive optics scanning laser ophthalmoscopy imaging of the retina and optoretinography (ORG).

Main outcome measures: Clinical/demographic data, multimodal retinal imaging data, electrophysiology parameters, and molecular genetic testing.

Results: Our cohort included a diverse set of subjects with CLN3-juvenile NCL (n = 3), TPP1-late infantile NCL (n = 5), PPT1-late infantile or juvenile NCL (n = 2), CLN6-infantile NCL (n = 1), and CLN7/MFSD8-late infantile NCL (n = 1). Five novel pathogenic or likely pathogenic variants were identified. Age at presentation ranged from 2 to 16 years old (mean 7.9 years). Subjects presented with varying phenotypes ranging from severe neurocognitive features (n = 8; 67%), including seizures and developmental delays and regressions, to nonsyndromic retinal dystrophies (n = 2; 17%). Visual acuities at presentation ranged from light perception to 20/20. In those with recordable ERGs, the traces were electronegative and suggestive of early cone dysfunction. Fundus imaging and OCTs demonstrated outer retinal loss that varied with underlying genotype. High-resolution adaptive optics imaging and functional measures with ORG in 2 subjects with atypical TPP1-associated disease revealed significantly different phenotypes of cellular structure and function that could be followed longitudinally.

Conclusions: Our cohort data demonstrates that the underlying genetic variants drive the phenotypic diversity in different forms of NCL. Genetic testing can provide molecular diagnosis and ensure appropriate disease management and support for children and their families. With intravitreal enzyme replacement therapy on the horizon as a potential treatment option for NCL-associated retinal degeneration, precise structural and functional measures will be required to more accurately monitor disease progression. We show that adaptive optics imaging and ORG can be used as highly sensitive methods to track early retinal changes, which can be used to establish eligibility for future therapies and provide metrics for determining the efficacy of interventions on a cellular scale.

Financial disclosures: Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Keywords: Adaptive optics; Genetic testing; Juvenile neuronal ceroid lipofuscinosis; Neuronal ceroid lipofuscinoses; Optoretinography.

Figure 1

CLN3-related neuronal ceroid lipofuscinoses can exhibit extraocular and isolated retinal findings. A, In subject 1 with systemic features of disease, there are extensive bone spicule-like pigmentary changes on fundus imaging with fundus autofluorescence demonstrating widespread hypoautofluoresence (white arrows). In contrast, in (B) subject 3 the OCT images demonstrate loss of outer segments with relative foveal preservation with a thickened external limiting membrane. Fundus photos show peripheral bone spicules (white arrows) and fundus autofluorescence shows bulls eye hyperautofluorescence in the macula (yellow arrow).

Figure 2

The genotypic determinants of phenotypic features of TPP1-related neuronal ceroid lipofuscinoses. A, electroretinographys of subjects 5 and 6 demonstrated attenuated traces compared to subjects 7 and 8. In subject 6 there is a characteristic electronegative electroretinography in the photophic traces (light adapted 3.0). In both subjects 6 and 7 there are features of early cone bipolar cell dysfunction with photopic b-wave prolongation. B, OCT scans of subjects 5 and 6 were done using a handheld system that shows focal disruption in the fovea. In subject 7 there is patchy loss of the retinal layers with patchy areas of hyperreflective foci (yellow arrowheads) whereas the OCT in subject 8 shows more preserved foveal architecture with lack of hyperreflective foci. C, Fundus photos show bull’s eye pattern of hyperautofluorescence (yellow arrows) in subject 7 whereas subject 8 has only focal area of hyper autofluorescence at the fovea (yellow arrows).

Figure 3

Genotypic variants of PPT1 can lead to differential retinal phenotypes and progressive features. A, In Subject 9 with classic systemic features of neuronal ceroid lipofuscinoses, the exam was consistent with a bulls eye maculopathy as evidenced on fundus autofluorescence (white arrow). Over the course of 1 year follow-up, OCT findings showed progressive loss of the outer retinal layers which correlated with decline in best-corrected visual acuity. B, In subject 10 with more isolated retinal findings and genotypic findings consistent with granular osmiophilic deposit, the exam was again consistent with a bulls eye maculopathy as evidenced on fundus autofluorescence (white arrow), but OCT findings were most notable for almost total loss of the outer retinal bands with hyperreflective foci in the fovea that progressively enlarged over the course of 12 months (yellow arrows).

Figure 4

Adaptive optics imaging of siblings with atypical, late-onset TPP1-related neuronal ceroid lipofuscinoses. Fundus auto-fluorescence images of subjects 7 and 8, respectively, are shown in panels (A) and (D) with overlain corresponding adaptive optics scanning laser ophthalmoscopy (AOSLO) (yellow box) and OCT b-scan (green line) locations. Panels (B) and (E) show AOSLO confocal montage images vertically (foveal center marked with asterisk) aligned to OCT b-scans in panels (C) and (F), respectively. The streaks of the cone mosaic in AOSLO images of subject 7 in panel B correlated to the disrupted outer segment region on OCT (yellow arrowheads). Comparatively, a well ordered cone mosaic on AOSLO in subject 8 corresponds to well preserved outer segments seen on OCT.

Figure 5

Adaptive optics scanning laser ophthalmoscopy imaging allows for precise cone density measurement in subject 8. Control values (black circles) are a running average of 0.35° bins from 7 control subjects. Error bars are the 95% confidence interval. Each subject 8 data point (red triangles) is from a confocal adaptive optics scanning laser ophthalmoscopy image in the temporal meridian.

Figure 6

Optoretinography in subject 8 is normal when compared to an age-matched control. A, Line-scan OCT volume was segmented to yield an en face image at the inner-outer segment junction (left: subject 8, right: control) annuli indicate eccentricities from fovea to 4 degrees temporal. B, optoretinography (ORG) traces for Subject 8 (left) and control (right) showing comparable response kinetics and amplitude across eccentricity. C, Structure-function maps, created by combining the OCT structure and ORG function for subject 8 (left) and normal control (right) show a similar trend in ORG response fall-off vs. eccentricity.