The Whole Exome Sequencing Clarifies the Genotype- Phenotype Correlations in Patients with Early-Onset Dementia

Abstract

Our study aimed to identify the underlying causes in patients with early onset dementia by clinical and genetic exploration. We recruited a group of 38 patients with early-onset dementia. Firstly, hexanucleotide repeat expansions in C9ORF72 gene were screened in all subjects to exclude the possibility of copy number variation. Then, the whole exome sequencing (WES) was conducted, and the data were analyzed focusing on 89 dementia-related causing and susceptible genes. The effects of identified variants were classified according to the American College of Medical Genetics and Genomics (ACMG) standards and guidelines. There were no pathogenic expansions in C9ORF72 detected. According to the ACMG standards and guidelines, we identified five known pathogenic mutations, PSEN1 P284L, PSEN1c.857-1G>A, PSEN1 I143T, PSEN1 G209E and MAPT G389R, and one novel pathogenic mutation APP K687N. All these mutations caused dementia with the mean onset age of 38.3 (range from 27 to 51) and rapid progression. Eleven variants with uncertain significance were also detected and needed further verification. The clinical phenotypes of dementia are heterogeneous, with both onset ages and clinical features being influenced by mutation position as well as the causative gene. WES can serve as efficient diagnostic tools for different heterogeneous dementia.

Keywords: Alzheimer’s disease; frontotemporal dementia; next-generation sequencing; variants classification.

Figure 1.. Magnetic resonance imaging (MRI), Alzheimer’s disease (AD) pathogenic mutations and Pedigrees for five cases

Brain MRI (T2W-FLAIR) images from AT001 (A), AT002 (D), AT040 (J), AT045 (M) and brain MRI (T2WI) images from AT003 (G). (B, E, H, K, N) are the Sanger sequencing results of AT001, AT002, AT003, AT040, and AT045. (C, F, I, L, O) indicate pedigrees of AT001, AT002, AT003, AT040, and AT045. * T2W-FLAIR: T2 weighted fluid-attenuated inversion recovery; T2WI: T2-weighted imaging.