ClinVar

Description

The c.1168A>G (p.M390V) alteration is located in exon 8 (coding exon 8) of the SPAST gene. This alteration results from a A to G substitution at nucleotide position 1168, causing the methionine (M) at amino acid position 390 to be replaced by a valine (V). The alteration is not observed in healthy cohorts:_x000D_ Based on data from the NHLBI Exome Sequencing Project (ESP), the SPAST c.1168A>G alteration was not observed among 6,503 individuals tested. Allele frequency data for this nucleotide position are not currently available from the 1000 Genomes Project and the alteration is not currently listed in the Database of Single Nucleotide Polymorphisms (dbSNP)._x000D_ Though some variants may appear to be rare due to database-specific ethnic underrepresentation, rare missense alleles commonly exhibit a deleterious effect on protein function (Kryukov, 2007; Tennessen, 2012). IF USED, PULL THESE INTO REFERENCES:_x000D_ Kryukov GV, et al. (2007) Am J Hum Genet 80:727-739. Tennessen JA, et al. (2012) Science 337(64):64-69. The amino acid change has been observed in affected individuals: _x000D_ This amino acid alteration was reported in several members of a Chinese family with HSP (Tang, 2004). Both pure and complicated HSP patients were seen in this family, with their clinical features including an early age of onset (mean 4.5 years), cognitive deficit, ataxia, epilepsy, and amyotrophy of the lower extremities. This alteration was also seen in de novo form in a Spanish patient with sporadic complicated HSP (Álvarez, 2010). The altered amino acid is conserved throughout evolution:_x000D_ The p.M390 amino acid position is completely conserved in available vertebrate species. The amino acid is located in a functionally important protein domain:_x000D_ The p.M390V amino acid is located in the AAA-ATPase domain of the spastin protein. The highly-conserved AAA cassette contains Walker A and B motifs (sites of ATP binding and ATPase activity), a helix-loop-helix dimerization domain, and a leucine zipper motif (Svenson, 2001). Most mutations in SPG4 affect this domain, and are associated with a trend towards earlier disease onset (Lourerio, 2013). The alteration is predicted deleterious by in silico models:_x000D_ The p.M390V alteration is predicted to be possibly damaging by Polyphen and deleterious by SIFT in silico analyses. Based on the available evidence, this alteration is classified as pathogenic.