Mutations

PSEN1 I238M

Overview

Pathogenicity: Alzheimer's Disease : Likely Pathogenic
Clinical Phenotype: Alzheimer's Disease
Reference Assembly: GRCh37/hg19
Position: Chr14:73659517 C>G
dbSNP ID: NA
Coding/Non-Coding: Coding
Mutation Type: Point, Missense
Codon Change: ATC to ATG
Reference Isoform: PSEN1 Isoform 1 (467 aa)
Genomic Region: Exon 7

Findings

This variant was found in a 60-year-old man with a family history of dementia, including four affected members (Wojtas et al., 2012). He was part of a cohort with onset of clinical probable Alzheimer’s disease (AD) before age 70 at the Mayo Clinic in Jacksonville, Florida. Members of the cohort were screened for mutations in genes associated with AD and frontotemporal dementia (exon 16 and 17 of APP, exons 3-12 of PSEN1, and exons 3-12 of PSEN2). His first symptoms were memory and vision loss and his APOE genotype was E3/E4.

The variant was also identified in an African-American woman diagnosed with probable AD who had a family history of AD/dementia (Ting et al., 2014). Her presentation was fairly typical of AD, starting with short-term memory loss, poor concentration, an inability to multitask, and increased anxiety. These symptoms began at age 50 and gradually progressed to multiple cognitive domains and impairment of activities of daily living. This patient was enrolled in the longitudinal study, the Dominantly Inherited Alzheimer Network (DIAN).

The patient's father was diagnosed with AD in his late 50s and died at the age of 65. Her paternal aunt and grandmother also died with dementia, but age of onset and age at death were not known. It was not possible to confirm disease segregation in this family, as DNA was not available from other affected members (who were all deceased) or unaffected members of the family.

This variant was absent from more than 2,000 African-Americans screened in the NHLBI GO sequencing project and from the gnomAD variant database (gnomAD v2.1.1, July 2021).

Neuropathology

Unknown; MRI showed progressive cerebral atrophy. PET showed hypometabolism in the frontal and temporal lobes.

Biological Effect

When expressed in HEK293 cells expressing APP with the Swedish mutation, the mutant PSEN1 increased Aβ40, Aβ42, and the Aβ42/Aβ40 ratio compared with cells expressing wild-type PSEN1 (Ting et al., 2014; see also Ringman et al., 2011). However, in an in vitro assay using purified proteins to test the mutant's ability to cleave the APP-C99 substrate, the mutation appeared to abrogate production of both Aβ40 and Aβ42 (Sun et al., 2017).

Several in silico algorithms (SIFT, Polyphen-2, LRT, MutationTaster, MutationAssessor, FATHMM, PROVEAN, CADD, REVEL, and Reve in the VarCards database) predicted this variant is damaging (Xiao et al., 2021).

Probable pathogenicity was suspected based on the early onset of symptoms, the family history of dementia, the absence of the mutation in variant databases, and the effects on Aβ levels in cultured cells (Ting et al., 2014).

Last Updated: 24 Aug 2021

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References

Paper Citations

  1. . C9ORF72 repeat expansions and other FTD gene mutations in a clinical AD patient series from Mayo Clinic. Am J Neurodegener Dis. 2012;1(1):107-18. PubMed.
  2. . A novel PSEN1 mutation (I238M) associated with early-onset Alzheimer's disease in an African-American woman. J Alzheimers Dis. 2014;40(2):271-5. PubMed.
  3. . Biochemical, neuropathological, and neuroimaging characteristics of early-onset Alzheimer's disease due to a novel PSEN1 mutation. Neurosci Lett. 2011 Jan 10;487(3):287-92. Epub 2010 Nov 19 PubMed.
  4. . Analysis of 138 pathogenic mutations in presenilin-1 on the in vitro production of Aβ42 and Aβ40 peptides by γ-secretase. Proc Natl Acad Sci U S A. 2017 Jan 24;114(4):E476-E485. Epub 2016 Dec 5 PubMed.
  5. . APP, PSEN1, and PSEN2 Variants in Alzheimer's Disease: Systematic Re-evaluation According to ACMG Guidelines. Front Aging Neurosci. 2021;13:695808. Epub 2021 Jun 18 PubMed.

External Citations

  1. the Dominantly Inherited Alzheimer Network (DIAN)
  2. NHLBI GO sequencing project
  3. gnomAD v2.1.1

Further Reading

No Available Further Reading

Protein Diagram

Primary Papers

  1. . A novel PSEN1 mutation (I238M) associated with early-onset Alzheimer's disease in an African-American woman. J Alzheimers Dis. 2014;40(2):271-5. PubMed.

Other mutations at this position

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