Vision problems may be earliest symptom of Sanfilippo C: Study

Eye tissue in mouse model showed at least 50% fewer rod cells

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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A man covers one eye with his hand and eyeglasses appear over his other hand.

Light-sensing cells in the eyes become damaged and die in Sanfilippo syndrome type C before the onset of behavioral symptoms, a new study indicates.

Issues related to vision “may be the first truly distinctive symptom” of Sanfilippo for these patients, which suggests “better disease awareness among ophthalmologists could play a critical role in early detection and diagnosis of patients,” the researchers wrote.

The study, “Histological characterization of retinal degeneration in mucopolysaccharidosis type IIIC,” was published in the journal Experimental Eye Research.

Vision problems are a common symptom of Sanfilippo syndrome. Experiments done in animal models of Sanfilippo types A and B have indicated the disease can cause death and degeneration of cells in the retina — the area at the back of the eyeball that houses the rod and cone cells that are used to detect light for vision.

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Checking for eye-related issues in mouse models

However, no studies have been done to assess eye-related disease in models of Sanfilippo type C, which is caused by mutations in the gene HGSNAT. This form of Sanfilippo tends to progress more slowly than types A and B.

To address this gap in research, team of scientists in the U.S. and Canada conducted detailed examinations of eye tissue in a mouse model of Sanfilippo type C.

The mice’s eyes were examined at 6 months of age, which is when the earliest signs of behavioral abnormalities are detectable in this model, and before neurological damage affecting memory and learning. This age was chosen to “determine if any [eye-related problems] developed before significant behavioral, or measurable neuronal loss arose,” the researchers wrote.

Results showed that, compared to wild-type (healthy) mice, the Sanfilippo C mice had at least 50% fewer rod cells in their retinas. Rods are good at detecting contrast and are critical for low-light vision.

Sanfilippo C mice did not show any noteworthy abnormalities affecting the other type of light-sensing cell, cones, which are needed to see colors.

To validate these results, the scientists also conducted an examination of eye tissue that was donated after death by a patient with Sanfilippo C. Consistent with the mouse results, findings indicated substantial loss of rod cells in this patient’s eye relative to a healthy donor matched for age, sex, and race.

“This result demonstrates for the first time that [Sanfilippo C] mice experience retinal degeneration in a manner that might be similar to human patients,” the researchers wrote.

Based on these data, the researchers speculated people with Sanfilippo C likely experience vision problems, and based on the timing of rod degeneration in mouse data, vision problems in patients might be one of the earliest detectable symptoms of the disease. This suggests eye exams could be useful for detecting and monitoring the disease, they said.

The scientists stressed that further research is needed to characterize how the eyes are affected in Sanfilippo in more detail.