SPG35 contributes to the second common subtype of AR-HSP in China: frequency analysis and functional characterization of FA2H gene mutations

Hereditary spastic paraplegias (HSPs) encompass a clinically and genetically heterogeneous group of neurodegenerative disorders. Recently, mutations in fatty acid 2-hydroxylase gene (FA2H) have been identified responsible for HSPs type 35 (SPG35). This study aims to define the contribution of FA2H to Chinese autosomal recessive HSP (AR-HSP) patients and provide insights into the enzymatic functions of the novel mutations. Direct sequencing of FA2H was conducted in 31 AR-HSP families and 55 sporadic cases without SPG11, SPG15, SPG5 and SPG7 gene mutations. Enzymatic activity of the mutated proteins was further examined. Three novel mutations were found in two Chinese families, including two compound heterozygous mutations (c.388C>T/p.L130F and c.506+6C>G) and one homozygous mutation (c.230T>G/p.L77R). The c.506+6C>G splice-site mutation led to the deletion of exon 3. Measurement of enzymatic functions revealed a significant reduction in the enzymatic activity of FA2H associated with p.L130F and p.L77R. Overall, our data widens the spectrum of the mutations on FA2H, and functional analyses indicate that these mutations severely impair the enzymatic activity of FA2H. Furthermore, frequency analysis shows that SPG35 is the second most common subtype of AR-HSP in China.