A novel SLC17A5 variant in infantile sialic acid storage disease with hyporegenerative anemia: Neuroimaging insights and literature review

Infantile sialic acid storage disorder (ISSD) represents the most severe form of free sialic acid storage disease (FSASD), a rare lysosomal storage disorder caused by mutations in <i>SLC17A5</i>, which encodes the lysosomal sialic acid transporter sialin. These mutations lead to the accumulation of free sialic acid within lysosomes, resulting in multisystemic involvement. Through a case report and literature review, we explored the phenotypic spectrum of FSASD, with a particular focus on neurological manifestations and characteristic neuroimaging findings of ISSD. Our patient exhibited severe hypotonia shortly after birth, dysmorphic features, and hyporegenerative anemia, a clinical presentation that has not previously described in ISSD. Brain MRI revealed hypomyelination, periventricular white matter T1-hyperintensity and T2-hypointensity, callosal thinning, and optic atrophy, providing critical diagnostic clues. MR spectroscopy showed an elevated NAA-like peak, further supporting the suspicion of ISSD. Laboratory tests demonstrated increased chitotriosidase activity and elevated urinary excretion of free sialic acid. Next-generation sequencing identified compound heterozygosity for a known pathogenic variant and a previously unreported <i>SLC17A5</i> variant (c.709G>A), affecting a highly conserved transmembrane domain residue and predicted to be pathogenic. Our findings underscore the role of neuroimaging in the early diagnosis of ISSD and suggest a potential link between sialic acid metabolism and erythropoiesis, suggesting further investigation. Despite the lack of targeted therapies, recognizing FSASD remains essential for patient management and genetic counselling, ensuring appropriate clinical care and family support.