Experimental evidence for temporal uncoupling of brain Aß deposition and neurodegenerative sequelae.

Brain Aß deposition is a key early event in the pathogenesis of Alzheimer´s disease (AD), but the long presymptomatic phase and poor correlation between Aß deposition and clinical symptoms remain puzzling. To elucidate the dependency of downstream pathologies on Aß, we analyzed the trajectories of cerebral Aß accumulation, Aß seeding activity, and neurofilament light chain (NfL) in the CSF (a biomarker of neurodegeneration) in Aß-precursor protein transgenic mice. We find that Aß deposition increases linearly until it reaches an apparent plateau at a late age, while Aß seeding activity increases more rapidly and reaches a plateau earlier, coinciding with the onset of a robust increase of CSF NfL. Short-term inhibition of Aß generation in amyloid-laden mice reduced Aß deposition and associated glial changes, but failed to reduce Aß seeding activity, and CSF NfL continued to increase although at a slower pace. When short-term or long-term inhibition of Aß generation was started at pre-amyloid stages, CSF NfL did not increase despite some Aß deposition, microglial activation, and robust brain Aß seeding activity. A dissociation of Aß load and CSF NfL trajectories was also found in familial AD, consistent with the view that Aß aggregation is not kinetically coupled to neurotoxicity. Rather, neurodegeneration starts when Aß seeding activity is saturated and before Aß deposition reaches critical (half-maximal) levels, a phenomenon reminiscent of the two pathogenic phases in prion disease.

Acute targeting of pre-amyloid seeds in transgenic mice reduces Alzheimer-like pathology later in life.

Amyloid-ß (Aß) deposits are a relatively late consequence of Aß aggregation in Alzheimer's disease. When pathogenic Aß seeds begin to form, propagate and spread is not known, nor are they biochemically defined. We tested various antibodies for their ability to neutralize Aß seeds before Aß deposition becomes detectable in Aß precursor protein-transgenic mice. We also characterized the different antibody recognition profiles using immunoprecipitation of size-fractionated, native, mouse and human brain-derived Aß assemblies. At least one antibody, aducanumab, after acute administration at the pre-amyloid stage, led to a significant reduction of Aß deposition and downstream pathologies 6 months later. This demonstrates that therapeutically targetable pathogenic Aß seeds already exist during the lag phase of protein aggregation in the brain. Thus, the preclinical phase of Alzheimer's disease-currently defined as Aß deposition without clinical symptoms-may be a relatively late manifestation of a much earlier pathogenic seed formation and propagation that currently escapes detection in vivo.

CNGB3 mutation spectrum including copy number variations in 552 achromatopsia patients.

Achromatopsia is a rare autosomal recessive cone disorder characterized by color vision defects, photophobia, nystagmus, and severely reduced visual acuity. The disease is caused by mutations in genes encoding crucial components of the cone phototransduction cascade (CNGA3, CNGB3, GNAT2, PDE6C, and PDE6H) or in ATF6, involved in the unfolded protein response. CNGB3 encoding the beta subunit of the cyclic nucleotide-gated ion channel in cone photoreceptors is the major achromatopsia gene. Here, we present a comprehensive spectrum of CNGB3 mutations and their prevalence in a cohort of 1074 independent families clinically diagnosed with achromatopsia. Of these, 485 (45.2%) carried mutations in CNGB3. We identified a total of 98 different potentially disease-causing CNGB3 variants, 58 of which are novel. About 10% of patients with CNGB3 mutations only harbored a single heterozygous variant. Therefore, we performed quantitative real-time PCR in 43 of such single heterozygotes in search of the missing allele, followed by microarray-based comparative genomic hybridization and breakpoint mapping. We discovered nine different heterozygous copy number variations encompassing one to 10 consecutive exons in 16 unrelated patients. Moreover, one additional patient with a homozygous CNGB3 deletion encompassing exons 4-18 was identified, highlighting the importance of CNV analysis for this gene.