Overview

Clinical Phenotype: Alzheimer's Disease
Position: (GRCh38/hg38):Chr11:121608132 G>C
Position: (GRCh37/hg19):Chr11:121478841 G>C
dbSNP ID: rs777194720
Coding/Non-Coding: Coding
DNA Change: Substitution
Expected Protein Consequence: Missense
Codon Change: GGA to GCA
Reference Isoform: SORL1 Isoform 1 (2214 aa)
Genomic Region: Exon 38

Findings

The G1732A variant was first identified in a Swedish woman from the European Early-Onset Dementia Consortium (EU-EOD) dataset (Verheijen et al., 2016). Subsequently, additional information from her family was reported (Thonberg et al., 2017). Four family members in two generations were afflicted with dementia: Three—two siblings and a cousin in the second generation—were diagnosed with AD, while the parent of the siblings was diagnosed with normal pressure hydrocephalus. The ages of symptom onset for the AD patients ranged from 47 to 62 years; early symptoms included memory impairment, visuospatial deficits, anxiety, and depression. Genotype data were available from two of the AD cases, both of whom carried the G1732A mutation and were homozygous for the E4 allele of APOE.

Subsequently, this variant was reported in one of 5198 AD cases and none of 4491 controls in a dataset from the Alzheimer’s Disease Sequencing Project (ADSP), consisting of subjects of non-Hispanic Caucasian ancestry from whom whole-exome sequencing data were available (Campion et al., 2019).

In a study that included 15,808 Alzheimer’s cases and 16,097 control subjects from multiple European and American cohorts, including ADSP, this allele was observed once among the AD cases (Holstege et al., 2022). No additional carriers were found when this dataset was expanded to 18,959 AD cases and 21,893 controls (Holstege et al., 2023).

The G1732A variant is classified as likely benign by the criteria of Holstege et al. (Holstege et al., 2017) and is of uncertain significance according to the American College of Medical Genetics and Genomics (ACMG) guidelines. Neuropathology Structural MRI was performed in two of the Swedish AD patients. Hippocampal and cortical atrophy, as well as small hemorrhages in cortical regions, were observed (Thonberg et al., 2017).

Functional Consequences

Glycine-1732 is located in the second of SORL1’s six 3Fn domains—named for fibronectin, the protein in which homologous domains were first described. SORL1’s 3Fn-cassette mediates receptor dimerization, which facilitates retromer-dependent transport of cargo out of endosomes (Jensen et al., 2023). Based on domain mapping of disease mutations, Andersen and colleagues predicted that substitutions at this position are highly likely to increase AD risk: They identified seven disease-associated variants at equivalent positions in 3Fn domains in other proteins and noted that four of these variants involved substitution of a glycine that is located two residues downstream from another glycine, as is the case for SORLA G1732A (Andersen et al., 2023).

The glycine-to-alanine substitution was predicted to be deleterious by SIFT, Mutation Taster, and PolyPhen-2 (Campion et al., 2019).

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References

Paper Citations

1. Verheijen J, Van den Bossche T, van der Zee J, Engelborghs S, Sanchez-Valle R, Lladó A, Graff C, Thonberg H, Pastor P, Ortega-Cubero S, Pastor MA, Benussi L, Ghidoni R, Binetti G, Clarimon J, Lleó A, Fortea J, de Mendonça A, Martins M, Grau-Rivera O, Gelpi E, Bettens K, Mateiu L, Dillen L, Cras P, De Deyn PP, Van Broeckhoven C, Sleegers K. A comprehensive study of the genetic impact of rare variants in SORL1 in European early-onset Alzheimer's disease. Acta Neuropathol. 2016 Aug;132(2):213-24. Epub 2016 Mar 30 PubMed.
2. Thonberg H, Chiang HH, Lilius L, Forsell C, Lindström AK, Johansson C, Björkström J, Thordardottir S, Sleegers K, Van Broeckhoven C, Rönnbäck A, Graff C. Identification and description of three families with familial Alzheimer disease that segregate variants in the SORL1 gene. Acta Neuropathol Commun. 2017 Jun 9;5(1):43. PubMed.
3. Campion D, Charbonnier C, Nicolas G. SORL1 genetic variants and Alzheimer disease risk: a literature review and meta-analysis of sequencing data. Acta Neuropathol. 2019 Aug;138(2):173-186. Epub 2019 Mar 25 PubMed.
4. Holstege H, Hulsman M, Charbonnier C, Grenier-Boley B, Quenez O, Grozeva D, van Rooij JG, Sims R, Ahmad S, Amin N, Norsworthy PJ, Dols-Icardo O, Hummerich H, Kawalia A, Amouyel P, Beecham GW, Berr C, Bis JC, Boland A, Bossù P, Bouwman F, Bras J, Campion D, Cochran JN, Daniele A, Dartigues JF, Debette S, Deleuze JF, Denning N, DeStefano AL, Farrer LA, Fernández MV, Fox NC, Galimberti D, Genin E, Gille JJ, Le Guen Y, Guerreiro R, Haines JL, Holmes C, Ikram MA, Ikram MK, Jansen IE, Kraaij R, Lathrop M, Lemstra AW, Lleó A, Luckcuck L, Mannens MM, Marshall R, Martin ER, Masullo C, Mayeux R, Mecocci P, Meggy A, Mol MO, Morgan K, Myers RM, Nacmias B, Naj AC, Napolioni V, Pasquier F, Pastor P, Pericak-Vance MA, Raybould R, Redon R, Reinders MJ, Richard AC, Riedel-Heller SG, Rivadeneira F, Rousseau S, Ryan NS, Saad S, Sanchez-Juan P, Schellenberg GD, Scheltens P, Schott JM, Seripa D, Seshadri S, Sie D, Sistermans EA, Sorbi S, van Spaendonk R, Spalletta G, Tesi N, Tijms B, Uitterlinden AG, van der Lee SJ, Visser PJ, Wagner M, Wallon D, Wang LS, Zarea A, Clarimon J, van Swieten JC, Greicius MD, Yokoyama JS, Cruchaga C, Hardy J, Ramirez A, Mead S, van der Flier WM, van Duijn CM, Williams J, Nicolas G, Bellenguez C, Lambert JC. Exome sequencing identifies rare damaging variants in ATP8B4 and ABCA1 as risk factors for Alzheimer's disease. Nat Genet. 2022 Dec;54(12):1786-1794. Epub 2022 Nov 21 PubMed.
5. Holstege H, deWaal MW, Tesi N, vanderLee SJ, ADESconsortium, ADSPconsortium, StEP-ADconsortium, Knight-ADRC, UCSF/NYGC/UAB, Vogel M, vanSpaendonk R, Hulsman M, Andersen OM. Effect of prioritized SORL1 missense variants supports clinical consideration for familial Alzheimer's Disease. 2023 Jul 16 10.1101/2023.07.13.23292622 (version 1) medRxiv.
6. Holstege H, van der Lee SJ, Hulsman M, Wong TH, van Rooij JG, Weiss M, Louwersheimer E, Wolters FJ, Amin N, Uitterlinden AG, Hofman A, Ikram MA, van Swieten JC, Meijers-Heijboer H, van der Flier WM, Reinders MJ, van Duijn CM, Scheltens P. Characterization of pathogenic SORL1 genetic variants for association with Alzheimer's disease: a clinical interpretation strategy. Eur J Hum Genet. 2017 Aug;25(8):973-981. Epub 2017 May 24 PubMed.
7. Jensen AM, Kitago Y, Fazeli E, Vægter CB, Small SA, Petsko GA, Andersen OM. Dimerization of the Alzheimer's disease pathogenic receptor SORLA regulates its association with retromer. Proc Natl Acad Sci U S A. 2023 Jan 24;120(4):e2212180120. Epub 2023 Jan 18 PubMed.
8. Andersen OM, Monti G, Jensen AM, deWaal M, Hulsman M, Olsen JG, Holstege H. Relying on the relationship with known disease-causing variants in homologous proteins to predict pathogenicity of SORL1 variants in Alzheimer's disease. 2023 Feb 27 10.1101/2023.02.27.524103 (version 1) bioRxiv.

Further Reading

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