Mutations

PSEN1 R278I

Overview

Pathogenicity: Alzheimer's Disease : Pathogenic, Progressive Nonfluent Aphasia : Pathogenic
Clinical Phenotype: Alzheimer's Disease, Progressive Nonfluent Aphasia
Reference Assembly: GRCh37 (105)
Position: Chr14:73664802 G>T
dbSNP ID: rs63749891
Coding/Non-Coding: Coding
Mutation Type: Point, Missense
Codon Change: AGA to ATA
Reference Isoform: PSEN1 isoform 1 (467 aa)
Genomic Region: Exon 8
Research Models: 1

Findings

This mutation was detected in two siblings from a pedigree with four affected members over three generations (Godbolt et al., 2004). The clinical presentation of disease in this family was atypical. Neither of the two individuals for which detailed clinical information was available met criteria for AD. In both cases, the disease was characterized by early language impairment with relative preservation of episodic memory. Specifically, one family member presented with word-finding difficulty and speech impairment at the age of 48. Over the next eight years her condition deteriorated and she developed mutism, rigidity, myoclonus of the upper limbs, and a shuffling gait. She was diagnosed with progressive nonfluent aphasia (PNFA). Her brother developed symptoms at age 51. He also had word-finding difficulties along with impairments in other executive functions. His disease, described as an atypical clinical syndrome, was suspected to be an atypical presentation of AD.

Neuropathology

Neuropathological data are unavailable, but MRI in both cases showed multiple white matter-foci with no or minimal atrophy.

Biological Effect

In vitro, this mutation severely impairs endoproteolysis of presenilin-1 and causes a selective increase in secreted Aβ43, an aggregating and neurotoxic peptide, and an increase in the Aβ42/Aβ40 ratio (Nakaya et al., 2005, Saito et al., 2011, July 2011 newsSzaruga et al., 2015).  In knock-in mice, Aβ43 generated extensive plaques (Saito et al., 2011). Consistently, the mutant produced about 30 percent less Aβ42 and than wild-type PSEN1, and more Aβ43 than Aβ42, in transfected mouse embryonic fibroblasts (Veugelen et al., 2016; April 2016 news). Moreover, assays using purified PSEN1 complexes and a tagged APPC99 substrate revealed it is more sensitive to increased temperatures, suggesting the mutation destabilizes the interaction required for proteolysis of APPC99 and newly produced Aβn substrates, resulting in the release of longer Aβ peptides (Szaruga et al., 2017). 

Subseqeunt experiments analyzing the Aβ peptidome of neurons derived from two patient iPSC lines, indicated this mutant moderately increases Aβ42/Aβ40 and Aβ42/Aβ38 ratios, and more robustly increases the Aβ43/Aβ40 ratio (Arber et al., 2019; see April 2019 news). The Aβ38/Aβ40 ratio remained unchanged. The elevated ratios suggest inefficient carboxypeptidase activity, predisposing neurons to accumulate longer Aβ fragments. Western blot analyses revelead impaired autocatalysis required for PSEN1 maturation. In addition, the mutation showed impaired γ-secretase activity for ApoER2, a member of the low-density lipoprotein receptor family that has been implicated in LTP and neuronal migration (Wang et al., 2017).

As revealed by a cryo-electron microscopy study of the atomic structure of γ-secretase bound to an APP fragment, R278 appears to play a key role in stabilizing the hybrid β-sheet that forms between PSEN1 and APP in preparation for cleavage (Zhou et al., 2019).

 

Research Models

A knock-in mouse model expressing human presenilin-1 with the R278I mutation has been generated. As a homozygote it is embryonic lethal due to impaired endoproteolysis of presenilin-1 and loss of γ-secretase functioning. Heterozygous mice are viable and overproduce Aβ43. When crossed to an APP transgenic model, APP23, double mutants developed high levels of Aβ43 and accelerated amyloid pathology (Saito et al., 2011).

Last Updated: 06 Aug 2019

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

Research Models Citations

  1. APP23

News Citations

  1. What’s Another Amino Acid? Aβ43 Drives Amyloid Pathology
  2. Pathogenic Presenilin Mutations Generate Aβ43
  3. Familial Alzheimer’s Mutations: Different Mechanisms, Same End Result

Paper Citations

  1. . Potent amyloidogenicity and pathogenicity of Aβ43. Nat Neurosci. 2011 Aug;14(8):1023-32. PubMed.
  2. . A presenilin 1 R278I mutation presenting with language impairment. Neurology. 2004 Nov 9;63(9):1702-4. PubMed.
  3. . Random mutagenesis of presenilin-1 identifies novel mutants exclusively generating long amyloid beta-peptides. J Biol Chem. 2005 May 13;280(19):19070-7. PubMed.
  4. . Qualitative changes in human γ-secretase underlie familial Alzheimer's disease. J Exp Med. 2015 Nov 16;212(12):2003-13. Epub 2015 Oct 19 PubMed.
  5. . Familial Alzheimer's Disease Mutations in Presenilin Generate Amyloidogenic Aβ Peptide Seeds. Neuron. 2016 Apr 20;90(2):410-6. PubMed.
  6. . Alzheimer's-Causing Mutations Shift Aβ Length by Destabilizing γ-Secretase-Aβn Interactions. Cell. 2017 Jul 27;170(3):443-456.e14. PubMed.
  7. . Familial Alzheimer's disease patient-derived neurons reveal distinct mutation-specific effects on amyloid beta. Mol Psychiatry. 2019 Apr 12; PubMed.
  8. . Presenilin 1 mutations influence processing and trafficking of the ApoE receptor apoER2. Neurobiol Aging. 2017 Jan;49:145-153. Epub 2016 Oct 11 PubMed.
  9. . Recognition of the amyloid precursor protein by human γ-secretase. Science. 2019 Feb 15;363(6428) Epub 2019 Jan 10 PubMed.

Further Reading

Learn More

  1. Alzheimer Disease & Frontotemporal Dementia Mutation Database

Protein Diagram

Primary Papers

  1. . A presenilin 1 R278I mutation presenting with language impairment. Neurology. 2004 Nov 9;63(9):1702-4. PubMed.

Other mutations at this position

Alzpedia

Disclaimer: Alzforum does not provide medical advice. The Content is for informational, educational, research and reference purposes only and is not intended to substitute for professional medical advice, diagnosis or treatment. Always seek advice from a qualified physician or health care professional about any medical concern, and do not disregard professional medical advice because of anything you may read on Alzforum.