Mutations in SQSTM1 encoding p62 in amyotrophic lateral sclerosis: genetics and neuropathology

Abstract

Mutations in SQSTM1 encoding the sequestosome 1/p62 protein have recently been identified in familial and sporadic cases of amyotrophic lateral sclerosis (ALS). p62 is a component of the ubiquitin inclusions detected in degenerating neurons in ALS patients. We sequenced SQSTM1 in 90 French patients with familial ALS (FALS) and 74 autopsied ALS cases with sporadic ALS (SALS). We identified, at the heterozygote state, one missense c.1175C>T, p.Pro392Leu (exon 8) in one of our FALS and one substitution in intron 7 (the c.1165+1G>A, previously called IVS7+1 G-A, A390X) affecting the exon 7 splicing site in one SALS. These mutations that are located in the ubiquitin-associated domain (UBA domain) of the p62 protein have already been described in Paget's disease and ALS patients carrying these mutations had both concomitant Paget's disease. However, we also identified two novel missense mutations in two SALS: the c.259A>G, p.Met87Val in exon 2 and the c.304A>G, p.Lys102Glu in exon 3. These mutations that were not detected in 360 control subjects are possibly pathogenic. Neuropathology analysis of three patients carrying SQSTM1 variants revealed the presence of large round p62 inclusions in motor neurons, and immunoblot analysis showed an increased p62 and TDP-43 protein levels in the spinal cord. Our results confirm that SQSTM1 gene mutations could be the cause or genetic susceptibility factor of ALS in some patients.

Sequestosome-1 (SQSTM1) sequence variants in ALS cases in the UK: prevalence and coexistence of SQSTM1 mutations in ALS kindred with PDB

“…7,8 The p.(Pro392Leu) mutation segregates with PDB, and, although the binding of polyubiquitin remains intact, it causes a phenotype that is indistinguishable from those caused by mutations that truncate the entire domain. 27 Third, multiple studies have confirmed the existence of the p.(Pro392Leu) mutation in ALS from different populations, 3,5 and, in combination with the data presented here, it can be concluded that it is the most common mutation in the gene in ALS to date ( Table 1). The coexistence of the p.(Pro392Leu) mutation in a family with a C9ORF72 expansion is not unexpected as C9ORF72 has also been found in FALS cases harbouring SOD1, FUS or TARDBP mutations.…”

“…important role in the formation of complexes that participate in the NFkB signalling pathway. 26 Second, the coexistence of both PDB and ALS in the two families reported here and in other studies 5 is indicative that common pathogenic mechanisms underlie both these diseases. P62/SQSTM1 has an established causal role in PDB, and the p.(Pro392Leu) mutation is, in fact, the most common cause of PDB.…”

“…Analysis of all SQSTM1 variants that are predicted as being pathogenic in published cohorts, [3][4][5][6] and the current study demonstrated that pathogenic SQSTM1 variants are significantly associated with FALS with a combined odds ratio of 3.91 (P MH ¼ 0.0002, Supplementary Table 1). No significant association was found for SALS cases.…”

“…Further, similar inclusions have been demonstrated in ALS cases harbouring SQSTM1 mutations. 5 In spite of the phenotypic heterogeneity found in ALS, ALS/ FTLD and PDB and related disorders such as IBMPFD and POAG, the discovery of mutations in overlapping candidate genes, such as VCP, UBQLN2, CHMP2B and OPTN, points to a common pathogenic mechanism affecting the formation and clearance of misfolded proteins. 2 We previously reported that the genotypes of protein disulphide isomerase (P4HB), a redox enzyme that reduces formation of aberrant disulphide bonds, were associated with survival time of FALS, 28 supporting the hypothesis that factors interfering with proteostasis may modify disease progression and can be considered as therapeutic targets for ALS.…”

“…[3][4][5][6] However, because of lack of DNA in multiple members of FALS kindred, to date it has not been proved that any of these mutations are transmitted with disease in ALS. Nevertheless, among the coding mutations is p.(Pro392Leu), which is common in Paget's disease of bone (PDB), 7,8 where there is evidence of transmission of the mutation with disease in multiple kindred.…”