Overview

Pathogenicity: Alzheimer's Disease : Not Classified, Cerebral Amyloid Angiopathy
ACMG/AMP Pathogenicity Criteria: PS1, PS3, PM1, PM2
Clinical Phenotype: Alzheimer's Disease, Cerebral Amyloid Angiopathy
Coding/Non-Coding: Both
DNA Change: Duplication
Expected RNA Consequence: Duplication
Expected Protein Consequence: Duplication
Genomic Region: Chromosome 21

Findings

This APP duplication was found in a large French study reporting seven families with APP duplications and autosomal-dominant, early onset Alzheimer's disease. All probands met NINCDS-ADRDA criteria for probable AD and had a family history of disease (Wallon et al., 2012). Duplications were detected by analyzing the APP locus on chromosome 21 using quantitative multiplex PCR of short fluorescent fragments (QMPSF)—a method that simultaneously amplifies multiple short genomic sequences.

The proband’s family (EXT 145) included two brothers who had lobar hemorrhage (Wallon et al., 2012, Grangeon et al., 2023). Ages at onset were 48 and 52 years. The brother with the earlier onset died after six years of illness.  Genetic analysis was performed only on the living proband, who carried a ~6Mb duplication with 13 genes, including APP, spanning NCAM2 to EIF4A1P. He had an APOE3/E3 genotype.

APP duplications are rare or absent from the general population (Sharp et al., 2005) and appear to be a rare cause of early onset AD (e.g., Hooli et al., 2012; June 2013 news; Wang et al., 2023).

Neuropathology
Neuropathological data are unavailable, but a brain MRI scan of the proband revealed probable cerebral amyloid angiopathy (CAA) with three intracerebral hemorrhages and 13 cerebral microbleeds (Grangeon et al., 2023).

Biological Effect
The biological effect of this specific APP duplication is unknown, but a study of multiple carriers of APP duplications showed that, as expected, the median levels of APP mRNA in blood were approximately 1.4-fold higher in carriers compared with non-carriers (Pottier et al., 2012). However, variability between duplications and individual carriers suggests other factors, such as the specific genes included in the duplication, may modulate expression (e.g., Lott and Head, 2019).

Of note, APP is in a recombination hotspot harboring multiple low copy repeats that may facilitate APP duplication (Sleegers et al., 2006; Rovelet-Lecrux et al., 2006).

Pathogenicity

Alzheimer's Disease : Not Classified*

*This variant fulfilled some ACMG-AMP criteria, but it was not classified by Alzforum, because only one affected carrier has been reported without co-segregation data, and the variant is absent—or very rare—in the gnomAD database.

This variant fulfilled the following criteria based on the ACMG/AMP guidelines. See a full list of the criteria in the Methods page.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

1. Do Copy Number Variations Point to Potential AD Genes? 27 Jun 2013

Paper Citations

1. Wallon D, Rousseau S, Rovelet-Lecrux A, Quillard-Muraine M, Guyant-Maréchal L, Martinaud O, Pariente J, Puel M, Rollin-Sillaire A, Pasquier F, Le Ber I, Sarazin M, Croisile B, Boutoleau-Bretonnière C, Thomas-Antérion C, Paquet C, Moreaud O, Gabelle A, Sellal F, Sauvée M, Laquerrière A, Duyckaerts C, Delisle MB, Streichenberger N, Lannes B, Frebourg T, Hannequin D, Campion D. The French series of autosomal dominant early onset Alzheimer's disease cases: mutation spectrum and cerebrospinal fluid biomarkers. J Alzheimers Dis. 2012 Jan 1;30(4):847-56. PubMed.
2. Grangeon L, Charbonnier C, Zarea A, Rousseau S, Rovelet-Lecrux A, Bendetowicz D, Lemaitre M, Malrain C, Quillard-Muraine M, Cassinari K, Maltete D, Pariente J, Moreaud O, Magnin E, Cretin B, Mackowiak MA, Sillaire AR, Vercelletto M, Dionet E, Felician O, Rod-Olivieri P, Thomas-Antérion C, Godeneche G, Sauvée M, Cartz-Piver L, Le Ber I, Chauvire V, Jonveaux T, Balageas AC, Laquerriere A, Duyckaerts C, Vital A, de Paula AM, Meyronet D, Guyant-Marechal L, Hannequin D, Tournier-Lasserve E, Campion D, CNR-MAJ collaborators, Nicolas G, Wallon D. Phenotype and imaging features associated with APP duplications. Alzheimers Res Ther. 2023 May 11;15(1):93. PubMed.
3. Sharp AJ, Locke DP, McGrath SD, Cheng Z, Bailey JA, Vallente RU, Pertz LM, Clark RA, Schwartz S, Segraves R, Oseroff VV, Albertson DG, Pinkel D, Eichler EE. Segmental duplications and copy-number variation in the human genome. Am J Hum Genet. 2005 Jul;77(1):78-88. Epub 2005 May 25 PubMed.
4. Hooli BV, Mohapatra G, Mattheisen M, Parrado AR, Roehr JT, Shen Y, Gusella JF, Moir R, Saunders AJ, Lange C, Tanzi RE, Bertram L. Role of common and rare APP DNA sequence variants in Alzheimer disease. Neurology. 2012 Apr 17;78(16):1250-7. Epub 2012 Apr 4 PubMed.
5. Wang H, Dombroski BA, Cheng P-L, Tucci A, Si Y-q, Farrell JJ, Tzeng J-Y, Leung YY, Malamon JS, Wang L-S, Vardarajan BN, Farrer LA, Schellenberg GD, Lee W-P. Structural Variation Detection and Association Analysis of Whole-Genome-Sequence Data from 16,905 Alzheimer's Diseases Sequencing Project Subjects. 2023 Sep 13 10.1101/2023.09.13.23295505 (version 1) medRxiv.
6. Pottier C, Wallon D, Lecrux AR, Maltete D, Bombois S, Jurici S, Frebourg T, Hannequin D, Campion D. Amyloid-β protein precursor gene expression in alzheimer's disease and other conditions. J Alzheimers Dis. 2012;28(3):561-6. PubMed.
7. Lott IT, Head E. Dementia in Down syndrome: unique insights for Alzheimer disease research. Nat Rev Neurol. 2019 Mar;15(3):135-147. PubMed.
8. Sleegers K, Brouwers N, Gijselinck I, Theuns J, Goossens D, Wauters J, Del-Favero J, Cruts M, van Duijn CM, Van Broeckhoven C. APP duplication is sufficient to cause early onset Alzheimer's dementia with cerebral amyloid angiopathy. Brain. 2006 Nov;129(Pt 11):2977-83. Epub 2006 Aug 18 PubMed.
9. Rovelet-Lecrux A, Hannequin D, Raux G, Le Meur N, Laquerrière A, Vital A, Dumanchin C, Feuillette S, Brice A, Vercelletto M, Dubas F, Frebourg T, Campion D. APP locus duplication causes autosomal dominant early-onset Alzheimer disease with cerebral amyloid angiopathy. Nat Genet. 2006 Jan;38(1):24-6. Epub 2005 Dec 20 PubMed.

Further Reading

No Available Further Reading