Sialidosis type 1 without cherry-red spots: a case report and literature review.

Background: Sialidosis is a rare disorder caused by mutations in the NEU1 gene located on chromosome 6p21.3, constituting a group of autosomal recessive diseases. Enzyme activity analysis, electron microscopy examination and genetic testing are reliable methods for diagnosis. Despite previous reports on the disease, its rarity means that its clinical manifestations and prognosis still warrant attention due to the limited amount of information available. Methods: We report a case of a 40-year-old woman who was admitted to our hospital for worsening dysarthria of 16 years duration and facial and limb twitching that had been present for 2 years. Genetic testing was undertaken. Results: Genetic testing confirmed type I sialidosis, the first reported instance of this disease in the Hainan Free Trade Port in China. The patient did not have the typical cherry-red spot in the fundus. Despite aggressive treatment, she died of status epilepticus 2 months later. This result indicates that the disease has a poor prognosis. Discussion: Cherry-red spots in the fundus are characteristic features of type I sialidosis and it has been referred to as the cherry-red spot myoclonus syndrome. We hypothesise that environmental factors may also play a significant role. Overemphasis on the presence of cherry-red spots may mislead clinicians and delay diagnosis. Furthermore, patients presenting with isolated myoclonus should undergo visual evoked potential and somatosensory evoked potential tests, as well as genetic testing to confirm or rule out sialidosis.