Clinical and pathologic features of chromosome 21-linked familial Alzheimer's disease

Prominent amyloid plaque pathology and cerebral amyloid angiopathy in APP V717I (London) carrier - phenotypic variability in autosomal dominant Alzheimer's disease

The discovery of mutations associated with familial forms of Alzheimer's disease (AD), has brought imperative insights into basic mechanisms of disease pathogenesis and progression and has allowed researchers to create animal models that assist in the elucidation of the molecular pathways and development of therapeutic interventions. Position 717 in the amyloid precursor protein (APP) is a hotspot for mutations associated with autosomal dominant AD (ADAD) and the valine to isoleucine amino acid substitution (V717I) at this position was among the first ADAD mutations identified, spearheading the formulation of the amyloid cascade hypothesis of AD pathogenesis. While this mutation is well described in multiple kindreds and has served as the basis for the generation of widely used animal models of disease, neuropathologic data on patients carrying this mutation are scarce. Here we present the detailed clinical and neuropathologic characterization of an APP V717I carrier, which reveals important novel insights into the phenotypic variability of ADAD cases. While age at onset, clinical presentation and widespread parenchymal beta-amyloid (Aβ) deposition are in line with previous reports, our case also shows widespread and severe cerebral amyloid angiopathy (CAA). This patient also presented with TDP-43 pathology in the hippocampus and amygdala, consistent with limbic predominant age-related TDP-43 proteinopathy (LATE). The APOE ε2/ε3 genotype may have been a major driver of the prominent vascular pathology seen in our case. These findings highlight the importance of neuropathologic examinations of genetically determined AD cases and demonstrate striking phenotypic variability in ADAD cases.

Psychiatric genetics: research challenges and pathways forward

Lessons from past psychiatric genetic research, together with key issues in psychiatry requiring genetic investigation, are reviewed in order to consider the implications for the ways forward. It is argued that traditional quantitative genetics needs to use a combination of twin, adoptee, and family strategies, to examine continuities and discontinuities in psychopathology between childhood and adult life, to compare dimensions and categories, to employ adequate conceptualization and measurement of disorders, to use statistical techniques based on latent constructs, to use biological trait indicators where possible, to examine risk factors as well as diseases, to include good measures of postulated environmental risk variables, to study the interplay between genes and environment, and to study the key assumptions underlying genetic strategies. Molecular cytogenetics needs to consider both the general and specific psychopathological risks associated with chromosome abnormalities and to examine the mechanism involved, to examine the role of submicroscopic chromosomal deletions and of mitochondrial disorders, and to investigate the mechanisms involved in trinucleotide repeat amplifications that take place during intergenerational transmission. Molecular genetics needs to make greater use of smaller pedigrees in view of the concerns over phenotypic definition and genetic heterogeneity in very large extended dense pedigrees, to use sib-pair designs in view of the likelihood that most psychiatric disorder will prove to be multifactorial, to combine association strategies with linkage analyses, to pay careful attention to the definition of phenotypes in probands, to remain in close touch with other branches of biological psychiatry, and to make effective use of collaboration between centers. To date, transgenic models have had a rather limited application in psychiatry but, despite their difficulties, they are likely to provide an underpinning for gene therapy in disorders where that seems feasible.