Mutations

PSEN2 R62H

Overview

Pathogenicity: Alzheimer's Disease : Benign, Frontotemporal Dementia : Benign
Clinical Phenotype: Alzheimer's Disease, Frontotemporal Dementia, Parkinson's Disease Dementia
Reference Assembly: GRCh37/hg19
Position: Chr1:227071449 G>A
dbSNP ID: rs58973334
Coding/Non-Coding: Coding
Mutation Type: Point, Missense
Codon Change: CGC to CAC
Reference Isoform: PSEN2 Isoform 1 (448 aa)
Genomic Region: Exon 5

Findings

The R62H variant has been found in people with a variety of neurodegenerative diseases (e.g., Alzheimer's disease, frontotemporal dementia, and Parkinson's disease), as well as in healthy controls. In the ExAC variant database, it is present at a 0.009890 frequency, but the frequency is higher in some populations, reaching nearly 4 percent in Africans (ExAC v.1.0, Oct 2020). It does not segregate with disease in the families for which data are available, and is therefore not thought to be pathogenic. Although R62H does not appear to cause familial disease, it may be a disease modifier. After correcting for APOE genotype, AD patients carrying the R62H variant were found to have an earlier age of onset than non-carriers (71 versus 75 years) (Cruchaga et al., 2012).

This variant was first reported in a patient with apparently sporadic Alzheimer's disease who developed symptoms at age 62 (Cruts et al., 1998). It was later found in a patient with late-onset Alzheimer's, but it did not segregate with disease within the family (Sleegers et al., 2004).

A large number of control individuals were later found to carry the R62H variant, suggesting it may be a benign polymorphism. Specifically, the R62H variant was found in 20 African individuals, leading the authors to speculate that it may be a relatively common polymorphism in some African populations (Guerreiro et al., 2010).

This variant was also found in a patient diagnosed with frontotemporal dementia. The patient was 31 years old when she began to experience behavioral disturbances and personality changes. The variant did not segregate with disease; it was found in the patient's cognitively healthy mother but was absent in an affected sibling (Gallo et al., 2010).

The variant was also found in a Turkish man with a family history of AD. The proband developed symptom onset at age 63 and developed symptoms of parkinsonism. The reported pedigree shows that his mother and maternal grandmother were also affected by dementia with apparent autosomal-dominant transmission. Segregation with disease could not be determined due to lack of DNA from family members (Lohmann et al., 2012).

This variant was also found in an individual with idiopathic Parkinson's disease with dementia (Schulte et al., 2015). The patient first developed symptoms of bradykinesia at age 81 and had a three-year disease duration. Other symptoms included rigidity and postural instability. The PD phenotype in this individual is considered unlikely to be attributable to the presence of this variant.

Most recently, this variant was found in one out of 72 individuals with AD. There was no family history of AD, and the clinical details related to this case were not reported (Frigerio et al., 2015).

Neuropathology

Neuropathological data are unavailable. However, cerebrospinal fluid biomarkers from two carriers suffering from AD suggest variability. Whereas one carrier, with an APOE3/3 genotype, had increased levels of Aβ40, Aβ42, and Aβ43, with an Aβ42/Aβ40 ratio in the normal range, another carrier, with an APOE3/4 genotype, had reduced levels of the Aβ40, Aβ42, and Aβ43, with a reduced Aβ42/Aβ40 ratio (Perrone et al., 2020). In both cases, sAPPα, and sAPPβ were reduced. Also, whereas the APOE3/3 carrier of the R62H variant had moderately increased levels of tau and normal levels of phospho-tau, the APOE3/4 carrier of the R62H variant had robustly elevated levels of both tau and phospho-tau. 

Biological Effect

 As described above, CSF levels of Aβ peptides in carriers of this mutation are variable. When transfected into fibroblasts lacking endogenous PSEN1 or PSEN2, the R62H variant did not affect steady-state levels of the proteolytic products PSEN2-CTF and PSEN2-NTF compared with wild-type PSEN2. When co-transfected with APP carrying the Swedish mutation, the R62H mutation did not affect Aβ42 levels or the Aβ42/Aβ40 ratio (Walker et al., 2005). Similar results were seen in transfected HEK293 cells (To et al., 2006) and mouse neuroblastoma cells (Hsu et al., 2020). The R62 residue, located in the N-terminal of PSEN2, is conserved between PSEN1 and PSEN2 (it is R60 in PSEN1).

In silico, the R62H variant is predicted "benign" by PolyPhen and "tolerated" by SIFT (Hsu et al., 2020). It has been classified as not pathogenic according to the algorithm proposed by Guerreiro et al., 2010 (Lohmann et al., 2012; Hsu et al., 2020).

Last Updated: 28 Oct 2020

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References

Paper Citations

  1. . Rare variants in APP, PSEN1 and PSEN2 increase risk for AD in late-onset Alzheimer's disease families. PLoS One. 2012;7(2):e31039. PubMed.
  2. . Estimation of the genetic contribution of presenilin-1 and -2 mutations in a population-based study of presenile Alzheimer disease. Hum Mol Genet. 1998 Jan;7(1):43-51. PubMed.
  3. . Familial clustering and genetic risk for dementia in a genetically isolated Dutch population. Brain. 2004 Jul;127(Pt 7):1641-9. Epub 2004 May 6 PubMed.
  4. . Genetic screening of Alzheimer's disease genes in Iberian and African samples yields novel mutations in presenilins and APP. Neurobiol Aging. 2010 May;31(5):725-31. Epub 2008 Jul 30 PubMed.
  5. . Novel MAPT Val75Ala mutation and PSEN2 Arg62Hys in two siblings with frontotemporal dementia. Neurol Sci. 2010 Feb;31(1):65-70. Epub 2009 Sep 19 PubMed.
  6. . Identification of PSEN1 and PSEN2 gene mutations and variants in Turkish dementia patients. Neurobiol Aging. 2012 Aug;33(8):1850.e17-27. PubMed.
  7. . Rare variants in β-Amyloid precursor protein (APP) and Parkinson's disease. Eur J Hum Genet. 2015 Jan 21; PubMed.
  8. . Amyloid-β1-43 cerebrospinal fluid levels and the interpretation of APP, PSEN1 and PSEN2 mutations. Alzheimers Res Ther. 2020 Sep 11;12(1):108. PubMed.
  9. . Presenilin 2 familial Alzheimer's disease mutations result in partial loss of function and dramatic changes in Abeta 42/40 ratios. J Neurochem. 2005 Jan;92(2):294-301. PubMed.
  10. . Functional characterization of novel presenilin-2 variants identified in human breast cancers. Oncogene. 2006 Jun 15;25(25):3557-64. PubMed.
  11. . Systematic validation of variants of unknown significance in APP, PSEN1 and PSEN2. Neurobiol Dis. 2020 Jun;139:104817. Epub 2020 Feb 19 PubMed.

Other Citations

  1. Frigerio et al., 2015

External Citations

  1. ExAC v.1.0, Oct 2020

Further Reading

Papers

  1. . Plasma amyloid beta protein is elevated in late-onset Alzheimer disease families. Neurology. 2008 Feb 19;70(8):596-606. Epub 2007 Oct 3 PubMed.
  2. . Mutation burden profile in familial Alzheimer's disease cases from India. Neurobiol Aging. 2018 Apr;64:158.e7-158.e13. Epub 2017 Dec 12 PubMed.

Protein Diagram

Primary Papers

  1. . Estimation of the genetic contribution of presenilin-1 and -2 mutations in a population-based study of presenile Alzheimer disease. Hum Mol Genet. 1998 Jan;7(1):43-51. PubMed.
  2. . Novel MAPT Val75Ala mutation and PSEN2 Arg62Hys in two siblings with frontotemporal dementia. Neurol Sci. 2010 Feb;31(1):65-70. Epub 2009 Sep 19 PubMed.

Other mutations at this position

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