Longitudinal in vivo monitoring of disease progression and viral mediated gene injection therapy in ovine Batten disease

Abstract

The neuronal ceroid-lipofuscinoses (NCLs; Batten disease) are a group of fatal neurodegenerative lysosomal storage diseases of children caused by a large number of mutations in up to 13 different genes. Forms associated with mutations in two of these, CLN5 and CLN6, are being investigated in well-established sheep models. Defining common features are progressive atrophy of the brain and retina, leading to psychomotor degeneration and blindness. Recent and on-going viral mediated gene therapy trials in the sheep are yielding results encouraging for clinical translation to humans1. In vivo assessments of brain atrophy and visual impairment are integral to the longitudinal monitoring individual animals and provide robust data for translation to treating human patients. Blindness in both sheep forms has a central and a peripheral component, as the visual cortex and the retina are both affected, thus it is important to monitor each separately to determine targets for treatment. Observations of the sheep in the field and during maze testing reveal occurrence of visual impairment that correlates with the onset of atrophy of the visual cortex (around 6 months of age), whereas electroretinography (ERG) indicates a later onset and slower development of retinal degeneration. In CLN5-/- sheep, the amplitudes of both a- and b-waves in the scotopic ERG become reduced from 7 months compared with controls (p < 0.05). CLN6 -/- animals show a slightly later onset of retinal degeneration, with both a- and b-wave amplitudes reduced from 11 months (p < 0.05). Computed tomography (CT) imaging shows an increase in skull thickness and a progressive reduction of intracranial volume (ICV) in affected animals. This reflects the course of cortical brain atrophy which generalises from the parieto-occipital cortex. ICVs of NCL affected sheep increase for the first few months, as in controls, but then decline progressively between 5 and 13 months in CLN5 -/- sheep and 11 to 15 months in CLN6-/- sheep (p < 0.05). Cerebral ventricular volume also increase with disease progression. These findings have been verified by magnetic resonance imaging (MRI) through which the regionality of brain atrophy can be visualised in greater detail. The combination of these modalities (ERG, CT and MRI) is integral to successful monitoring of large animal treatment trials and to obtain information for human translation.