Is the eye a window to the brain in Sanfilippo syndrome?

Sanfilippo syndrome is an untreatable form of childhood-onset dementia. Whilst several therapeutic strategies are being evaluated in human clinical trials including i.v. delivery of AAV9-based gene therapy, an urgent unmet need is the availability of non-invasive, quantitative measures of neurodegeneration. We hypothesise that as part of the central nervous system, the retina may provide a window through which to ‘visualise’ degenerative lesions in brain and amelioration of them following treatment. This is reliant on the age of onset and the rate of disease progression being equivalent in retina and brain. For the first time we have assessed in parallel, the nature, age of onset and rate of retinal and brain degeneration in a mouse model of Sanfilippo syndrome. Significant accumulation of heparan sulphate and expansion of the endo/lysosomal system was observed in both retina and brain pre-symptomatically (by 3 weeks of age). Robust and early activation of micro- and macroglia was also observed in both tissues. There was substantial thinning of retina and loss of rod and cone photoreceptors by ~ 12 weeks of age, a time at which cognitive symptoms are noted. Intravenous delivery of a clinically relevant AAV9-human sulphamidase vector to neonatal mice prevented disease lesion appearance in retina and most areas of brain when assessed 6 weeks later. Collectively, the findings highlight the previously unrecognised early and significant involvement of retina in the Sanfilippo disease process, lesions that are preventable by neonatal treatment with AAV9-sulphamidase. Critically, our data demonstrate for the first time that the advancement of retinal disease parallels that occurring in brain in Sanfilippo syndrome, thus retina may provide an easily accessible neural tissue via which brain disease development and its amelioration with treatment can be monitored.

DIAGNOSIS OF CHILDREN WITH SANFILIPPO DISEASE – PSYCHOLOGICAL, SOCIAL AND MOTOR ASSESSMENT

Sanfilippo disease (mucopolysaccharidosis, MPS IIIA) is one of the types of mucopolysaccharidosis associated with extensive neurological effects and somatic symptoms. The consequences of neurodegeneration and cognitive impairment are manifested in challenges with the daily functioning of patients who experience problems with communication and following instructions. The aim of this study was to assess the cognitive functioning of three patients with MPS IIIA and to find patterns of neurodegeneration and to make their environment more friendly. Three boys (from 5.5 to 7 years) with MPS IIIA participated in the study. Each participant attended two meetings, and his functioning was assessed by three independent person (using two-way mirror). We used Bayley’s Scale III with some modifications. Interviews with parents were also included. The communication of patients was limited to some vocalizations. Patients presented instrumental use of items, but not all of them were able to repeat actions after diagnostician or presented object permanence. The results showed that the cognitive functioning of participants was significantly hindered by problems related to motor dysfunction, hyperactivity, and ataxia. The psychological data was collated with medical results. This study allows indicating new sources giving the possibility of child phenotype variability and to create specific interventions in the field of psychological therapy for patients with MPS IIIA and their families.

Molecular Bases of Neurodegeneration and Cognitive Decline, the Major Burden of Sanfilippo Disease

The mucopolysaccharidoses (MPS) are a group of diseases caused by the lysosomal accumulation of glycosaminoglycans, due to genetic deficiencies of enzymes involved in their degradation. MPS III or Sanfilippo disease, in particular, is characterized by early-onset severe, progressive neurodegeneration but mild somatic involvement, with patients losing milestones and previously acquired skills as the disease progresses. Despite being the focus of extensive research over the past years, the links between accumulation of the primary molecule, the glycosaminoglycan heparan sulfate, and the neurodegeneration seen in patients have yet to be fully elucidated. This review summarizes the current knowledge on the molecular bases of neurological decline in Sanfilippo disease. It emerges that this deterioration results from the dysregulation of multiple cellular pathways, leading to neuroinflammation, oxidative stress, impaired autophagy and defects in cellular signaling. However, many important questions about the neuropathological mechanisms of the disease remain unanswered, highlighting the need for further research in this area.