[A novel mutation of SPAST gene in a hereditary spastic paraplegia type 4 family]

Objective: To clarify the pathogenicity and further explore the association between genotype and clinical phenotype of this variant, analyzing a novel variation of SPAST gene in hereditary spastic paraplegia (HSP) family from Changzhi city, Shanxi Province. Methods: A family with HSP was tracked and collected in Neurology Department of Heping Hospital Affiliated to Changzhi Medical College in October 2019. Peripheral venous blood of 2 ml was extracted from the proband and 8 other members of the family, genomic DNA was extracted from the blood samples, and the genes of spastic paraplegia were screened by next-generation sequencing (NGS). HGMD, 1000G, OMIM databases and PolyPhen2, SIFT and other software were used for bioinformatics analysis of suspected mutations. Multiplex ligation-dependent probe amplification (MLPA) was used to further screen for total deletions/duplications in patients who remained negative after targeting NGS, and Sanger sequencing was performed to verify the suspected pathogenic mutation sites in the family to determine co-isolation of the mutation sites in the family members. Finally, it is necessary to refer to the latest version of The American College of Medical Genetics and Genomics (ACMG) sequence variation interpretation guidelines to interpret the mutation sites to determine pathogenicity. Results: The HSP family consist 47 members of 4 generations and 10 patients, with onset ages ranging from 2 to 44 years. The proband's daughter only showed positive bilateral Babbitt signs on physical examination, and the rest of the patients showed spasticity and weakness of lower limbs with varying severity on this basis. Preliminary screening by next-generation sequencing technology showed that the proband had frame-shift variation of SPAST gene c.1057_1058insCC (p.Leu354HisfsTer11) and missense variation of DCTN1 gene c.2213A>G (p.Gln738Arg). Then, Sanger sequencing was used for in-family verification, which showed SPAST gene c.1057_1058insCC (p.Leu354HisfsTer11) was detected in the affected members include father, brother, son and daughter, and not detected in the unaffected normal members, the proband's wife, mother, sister and sister-in-law. However, the unaffected of mother detected missense variation of DCTN1 gene c.2213A>G (p.Gln738Arg), while the remaining members did not detect this variation. The results of MLPA showed that no large fragment variation was found. Conclusions: The genetic pattern of the HSP family was autosomal dominant, and the clinical characteristics were consistent with hereditary spastic paraplegia type 4 (SPG4). Co-segregation of SPAST gene c.1057_1058insCC (p.Leu354HisfsTer11) was found in the HSP family and was the pathogenicity cause of this SPG4 family, and it was a newly discovered mutation locus.