Mucopolysaccharidosis type IIIC in chinese mainland: clinical and molecular characteristics of ten patients and report of six novel variants in the HGSNAT gene

Background: Mucopolysaccharidosis type IIIC (MPS IIIC; Sanfilippo syndrome C) is a rare lysosomal storage disease caused by mutations in the heparan-α-glucosaminide N-acetyltransferase (HGSNAT) gene, resulting in the accumulation of heparan sulfate. MPS IIIC is characterized by severe neuropsychiatric symptoms and mild somatic symptoms.

Methods: Our study analyzed the clinical presentation and biochemical characteristics of ten Chinese MPS IIIC patients from eight families. Whole exome sequencing was applied to identify the variants in HGSNAT gene. In one patient with only one mutant allele identified firstly, whole genome sequencing was applied. The pathogenic effect of novel variants was evaluated in silico.

Results: The mean age at the onset of clinical symptoms was 4.2 ± 2.5 years old, and the mean age of diagnosis was 7.6 ± 4.5 years old, indicating a delay of diagnosis. The most common onset symptoms were speech deterioration, and the most frequent presenting symptoms are speech deterioration, mental deterioration, hyperactivity and hepatomegaly, sequentially. All mutant alleles of 10 patients have been identified. There were eleven different HGSNAT variants, and the most common one was a previously reported variant c.493 + 1G > A. There were six novel variants, p.R124T, p.G290A, p.G426E, c.743 + 101_743 + 102delTT, c.851 + 171T > A and p.V582Yfs*18 in our cohort. Extraordinarily, two deep intron variants were identified in our cohort, with the variant c.851 + 171T > A identified by whole genome sequencing.

Conclusion: This study analyzed the clinical, biochemical, and genetic characteristics of ten Chinese MPS IIIC patients, which would assist in the early diagnosis and genetic counselling of MPS IIIC.