Clinical characterization of a presenilin 1 mutation (F177S) in a family with very early‐onset Alzheimer's disease in the third decade of life

Screening for Genetic Mutations Associated with Early-Onset Alzheimer's Disease in Han Chinese

BACKGROUND

Early-onset Alzheimer's disease (EOAD) is highly influenced by genetic factors. Numerous mutations in amyloid precursor protein (APP) and presenilin 1 and 2 (PSEN1 and PSEN2) have been identified for EOAD, but they can only account for a small proportion of EOAD cases.

OBJECTIVE

This study aimed to screen genetic mutations and variants associated with EOAD among Han Chinese adults.

METHODS

This study included 34 patients with EOAD and 26 controls from a population-based study and neurological ward. We first sequenced mutations in APP/PSENs and then performed whole-exome sequencing in the remaining patients with negative mutations in APP/PSENs to screen for additional potential genetic variants. Among patients who were negative in genetic screening tests, we further evaluated the risk burden of genes related to the Aβ metabolism-centered network to search for other probable causes of EOAD.

RESULTS

We identified 7 functional variants in APP/PSENs in 8 patients, including 1 APP mutation (p. Val715Met), 3 PSEN1 mutations (p. Phe177Ser; p. Arg377Met; p. Ile416Thr), and 3 PSEN2 mutations (p. Glu24Lys; p. Gly34Ser; p. Met239Thr). Of the remaining 26 EOAD cases without mutations in APP/PSENs, the proportion of carrying rare variants of genes involved in Aβ and APP metabolism was significantly higher than that of controls (84.6% vs. 73.1%, P=0.042). Thirty-one risk genes with 47 variants were identified in 22 patients. However, in 26 normal subjects, only 20 risk genes with 29 variants were identified in 19 subjects.

CONCLUSIONS

Our findings demonstrate the role of APP/PSENs mutations in EOAD, identifying a new PSEN2 missense mutation, and further offer valuable insights into the potential genetic mechanisms of EOAD without APP/PSENs mutations among Han Chinese.

Very Early-Onset Alzheimer's Disease in the Third Decade of Life with de novo PSEN1 Mutations

Mutations in Presenilin-1 (PSEN1) have been found to be associated with very early onset Alzheimer's disease (VEOAD). Here, we reported two patients with VEOAD caused by de novo PSEN1 mutations. A 33-year-old man with a de novo p.F177S mutation in PSEN1 presented with progressive decline in memory and daily functioning. A 37-year-old woman with a de novo PSEN1 p.L381V mutation presented with onset memory impairment, developed cerebellar syndrome, rigidity, and spastic paraparesis. The Amyloid/Tau/Neurodegeneration (ATN) biomarker profiles of both patients were A + T + (N)+. Our finding increases the genetic knowledge of VEOAD and extends the ethnic distribution of PSEN1 mutations.

A Pathogenic Variant p.Phe177Val in PSEN1 Causes Early-Onset Alzheimer's Disease in a Chinese Family

Familial Alzheimer’s disease (FAD) present as a positive family history of cognitive decline, with early onset and an autosomal dominant inheritance pattern. FAD is mainly caused by the mutations in the genes encoding for amyloid precursor protein (APP), presenilin-1 (PSEN1), and presenilin-2 (PSEN2). In the present study, we identified a variant (c.529T > G, p.Phe177Val) in PSEN1 across three generations in a Chinese family with FAD using whole-exome sequencing. The mean age of onset was 39 years (range: 37 to 40 years) in this family. In cell transfection studies, the mutant PSEN1 protein carrying p.Phe177Val increased both the production of Aβ42 and the ratio of Aβ42 over Aβ40, as compared to wild-type PSEN1. Our results confirm the pathogenicity of PSEN1 p.Phe177Val variant in FAD and broaden the clinical phenotype spectrum of FAD patients with PSEN1 p.Phe177Val variant.

Presenilin-1 mutation is associated with a hippocampus defect in alzheimer's disease: Meta-Analysis for neuroimaging research

Observational studies suggested an association of the Presenilin-1 (PSEN1) genotype with neuroimaging markers within Alzheimer's disease. However, whether the PSEN1 genotype and neuroimaging markers is a harbinger of Alzheimer's disease remains controversial. We aimed to examine the association of the PSEN1 mutation with neuroimaging markers in Alzheimer's disease: hippocampal volume, cerebral metabolism and brain amyloid deposition. We performed a systematic review and meta-analysis of 13 studies identified in Pubmed and Medline from 1997 to 2019 (n = 164). The pooled standard mean difference (SMD) was used to evaluate the association between the PSEN1 mutation and hippocampal volume and cerebral metabolism rate for glucose (CMRgl). A meta-analysis was also performed regarding the amyloid deposition between the PSEN1+ and PSEN1- groups. In order to accurately study whether PSEN1 independently was associated with changes in related image markers, sub-meta analyses was performed. The PSEN1 mutation was associated with a smaller hippocampal volume (pooled SMD: -3.3; 95 % CI: -5.36 to -1.24; p = 0.002) and decreased cerebral metabolism (pooled SMD: -1.73; 95 % CI: -2.7 to -0.76; p < 0.0001). Additionally, PSEN1 was associated with increased cerebral amyloid deposition as detected by a positron emission tomography tracer (pooled SMD: 4.58; 95 % CI: 1.37-7.8; p = 0.0005). PSEN1 was associated with a decreased hippocampal volume in MRI markers, cerebral glucose hypometabolism, and increased cerebral amyloid deposition. These associations may indicate the potential role of neuroimaging markers for the diagnosis of Alzheimer's disease.

A novel V272D presenilin mutation associated with logopenia, disorientation, and apraxia in an autosomal-dominant Alzheimer's disease family

In the present study, a novel mutation in the presenilin 1 gene was discovered in an Iraq-native patient with early-onset Alzheimer's disease, who presented with speech impairment and memory decline at age 46 years. Magnetic resonance imaging showed a frontotemporal atrophy. Sanger sequencing identified a heterozygous T to A transversion at position 815 (c.815T>A) in the presenilin 1 gene (PSEN1), resulting in a novel missense mutation at codon 272 from valine to aspartate (V272D). We tested this PSEN1 mutation in vitro and found V272D resulted in an altered Aβ42/40 ratio.

Genetic influences on white matter and metabolism abnormal change in Alzheimer's disease: Meta-analysis for neuroimaging research on presenilin 1 mutation

Mutations in the presenilin1 (PSEN1) cause familial Alzheimer's disease (FAD), providing a special opportunity to study pre-symptomatic individuals who would be predicted to develop Alzheimer's disease (AD) in the future. However, whether presenilin1 (PSEN1) genotype and neuroimaging markers is a harbinger of AD remains controversial. We aimed to explore the association of PSEN1 genotype with neuroimaging markers of AD: white matter integrity, cerebral amyloid deposition and brain metabolism. We reviewed studies of diffusion tensor imaging (DTI), amyloid deposition and cerebral metabolism in patients with AD and control, in order to address the relative change of white matter microstructural associated with PSEN1 genotype. We performed a systematic meta-analysis and review of 11 cross-sectional studies identified in several database from 2008 to 2018 (n = 165). The pooled standard mean difference (SMD) value was calculated to estimate the association between PSEN1 and white matter change and brain metabolism. PSEN1 mutation carrier status was associated with mean diffusivity (MD) change (pooled SMD: 2.29; 95% CI 1.04 to 3.53; p < 0.001) and increased cerebral amyloid positron emission tomography tracer (pooled SMD: 3.78, 95% CI 1.04 to 6.53, p = 0.007). PSEN1 was not associated with white matter metabolism change (p = 0.069). PSEN1 was associated with mean diffusivity (MD) increase in DTI markers and decreased brain metabolism. Theses associations may suggest the potential role of the PSEN1 gene and imaging marker in Alzheimer's disease.

Mutation screening in Chinese patients with familial Alzheimer's disease by whole-exome sequencing

Familial Alzheimer's disease (FAD) is characterized by a positive family history of dementia and typically occurs at an early age with an autosomal dominant pattern of inheritance. Amyloid precursor protein (APP), presenilin1 (PSEN1), and presenilin2 (PSEN2) are the major causative genes of FAD. The spectrum of mutations in patients with FAD has been investigated extensively in the Caucasian population but rarely in the Chinese population. Here, we performed whole-exome sequencing in a total of 15 unrelated Chinese patients with FAD. Among them, 12 were found to carry missense variants in APP, PSEN1, and PSEN2. Two novel variants (APP: p.D244G, p.K687Q), 3 variants not previously associated with FAD (APP: p.T297M, p.D332G; PSEN1: p.R157S), and 7 previously reported pathogenic variants (APP: p.V717I; PSEN1: p.M139I, p.T147I, p.L173W, p.F177S, p.R269H; PSEN2: p.V139M) were identified. The novel variant APP p.K687Q was classified as likely pathogenic, and the other 4 variants (APP: p.D244G, p.T297M, p.D332G; PSEN1: p.R157S) were classified as uncertain significance. Therefore, APP, PSEN1, and PSEN2 mutations account for 2 (25.0%), 5 (62.5%), and 1 (12.5%) of the genotyped cases positive for mutations, respectively. Furthermore, the genotype-phenotype correlations were described. Our findings broaden the genetic spectrum of FAD with APP, PSEN1, and PSEN2 variants.