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Genetic influences on atrophy patterns in familial Alzheimer's disease: a comparison of APP and PSEN1 mutations.

ABSTRACT: Mutations in the presenilin1 (PSEN1) and amyloid ?-protein precursor (APP) genes account for the majority of cases of autosomal dominantly inherited Alzheimer's disease (AD). We wished to assess and compare the patterns of cerebral loss produced by these two groups of mutations. Volumetric magnetic resonance imaging and neuropsychological assessments were performed in individuals with clinical AD carrying mutations in the APP (n = 10) and PSEN1 (n = 18) genes and in healthy controls (n = 18). Voxel-based morphometry (VBM), cortical thickness, and region of interest analyses were performed. Mini-Mental State Examination scores were similar in the two disease groups suggesting similar levels of disease severity. There was evidence that APP subjects have smaller hippocampal volume compared with PSEN1 subjects (p = 0.007), and weak evidence that they have larger whole-brain and grey matter volumes (both p = 0.07). Although there was no evidence of statistically significant differences between APP and PSEN1 in VBM or cortical thickness analyses, effect-maps were suggestive of APP subjects having more medial temporal lobe atrophy and conversely PSEN1 subjects showing more neocortical loss. Neuropsychological data were consistent with these regional differences and suggested greater memory deficits in the APP patients and greater impairment in non-memory domains in the PSEN1 group, although these differences were not statistically significant. We conclude that the mechanisms by which APP and PSEN1 mutations cause neuronal loss may differ which furthers our understanding of the neuropathology underlying AD and may inform future therapeutic strategies and trial designs.

SUBMITTER: Scahill RI

PROVIDER: S-EPMC4982537 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Project description:BackgroundAmyloid protein precursor (APP), presenilin-1 (PSEN1), and presenilin-2 (PSEN2) mutations cause autosomal dominant forms of early-onset Alzheimer disease (AD-EOAD). Although these genes were identified in the 1990s, variant classification remains a challenge, highlighting the need to colligate mutations from large series.Methods and findingsWe report here a novel update (2012-2016) of the genetic screening of the large AD-EOAD series ascertained across 28 French hospitals from 1993 onwards, bringing the total number of families with identified mutations to n = 170. Families were included when at least two first-degree relatives suffered from early-onset Alzheimer disease (EOAD) with an age of onset (AOO) ≤65 y in two generations. Furthermore, we also screened 129 sporadic cases of Alzheimer disease with an AOO below age 51 (44% males, mean AOO = 45 ± 2 y). APP, PSEN1, or PSEN2 mutations were identified in 53 novel AD-EOAD families. Of the 129 sporadic cases screened, 17 carried a PSEN1 mutation and 1 carried an APP duplication (13%). Parental DNA was available for 10 sporadic mutation carriers, allowing us to show that the mutation had occurred de novo in each case. Thirteen mutations (12 in PSEN1 and 1 in PSEN2) identified either in familial or in sporadic cases were previously unreported. Of the 53 mutation carriers with available cerebrospinal fluid (CSF) biomarkers, 46 (87%) had all three CSF biomarkers-total tau protein (Tau), phospho-tau protein (P-Tau), and amyloid β (Aβ)42-in abnormal ranges. No mutation carrier had the three biomarkers in normal ranges. One limitation of this study is the absence of functional assessment of the possibly and probably pathogenic variants, which should help their classification.ConclusionsOur findings suggest that a nonnegligible fraction of PSEN1 mutations occurs de novo, which is of high importance for genetic counseling, as PSEN1 mutational screening is currently performed in familial cases only. Among the 90 distinct mutations found in the whole sample of families and isolated cases, definite pathogenicity is currently established for only 77%, emphasizing the need to pursue the effort to classify variants.

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Genetic influences on atrophy patterns in familial Alzheimer's disease: a comparison of APP and PSEN1 mutations.

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