SORL1 gene mutation and octapeptide repeat insertion in PRNP gene in a case presenting with rapidly progressive dementia and cerebral amyloid angiopathy

BACKGROUND

Cerebral amyloid angiopathy (CAA) has been associated with a variety of neurodegenerative disorders, included prion diseases (PrDs) and Alzheimer's disease (AD); its pathophysiology is still largely unknown. We report the case of an 80-year-old man with a rapidly progressive dementia and neuroimaging features consistent with CAA carrying two genetic defects in the PRNP and SORL1 genes.

METHODS

Neurological examination, brain Magnetic Resonance Imaging (MRI), electroencephalogram-electromyography (EEG-EMG) polygraphy and analysis of 14-3-3 and tau proteins, Aβ40 and Aβ42 in the cerebrospinal fluid (CSF) were performed. The patient underwent a detailed genetic study by next generation sequencing analysis.

RESULTS

The patient presented with progressive cognitive dysfunction, generalized myoclonus and ataxia. About 9 months after symptom onset, he was bed-bound, almost mute and akinetic. Brain MRI was consistent with CAA. CSF analysis showed high levels of t-tau and p-tau, decreased Aβ42, decreased Aβ42/Aβ40 ratio, while 14.3.3 protein was not detected. EEG-EMG polygraphy demonstrated diffuse slowing, frontal theta activity and generalized spikes-waves related to upper limb myoclonus induced by intermittent photic stimulation. Genetic tests revealed the presence of the E270K variant in the SORL1 gene and the presence of a single octapeptide repeat insertion (OPRI) in the coding region of the PRNP gene.

CONCLUSIONS

The specific pathogenic contribution of the two DNA variations is difficult to determine without neuropathology; among the possible explanations, we discuss the possibility of their link with CAA. Vascular and degenerative pathways actually interact in a synergistic way, and genetic studies may lead to more insight into pathophysiological mechanisms.

Association between Alzheimer's disease genes and trajectories of cognitive function decline in Han Chinese in Taiwan

Genetic background has been considered one of the important contributors to the rate of cognitive decline among patients with Alzheimer’s disease (AD). We conducted a 4-year longitudinal follow-up study, recruited 255 AD and 44 mild cognitive impairment (MCI) patients, and used a data-driven trajectory analysis to examine the influence of selected AD risk genes on the age for and the rate of cognitive decline in Han Chinese population. Genotyping of selected single-nucleotide polymorphisms in the APOE, ABCA7, SORL1, BIN1, GAB2, and CD33 genes was conducted, and a Bayesian hierarchical model was fitted to analyze the trajectories of cognitive decline among different genotypes. After adjusting for sex and education years, the APOE ε4 allele was associated with an earlier mean change of −2.39 years in the age at midpoint of cognitive decline, the G allele in ABCA7 rs3764650 was associated with an earlier mean change of −1.75 years, and the T allele in SORL1 rs3737529 was associated with a later mean change of 2.6 years. Additionally, the rate of cognitive decline was associated with the APOE ε4 allele and SORL1 rs3737529. In summary, APOE and SORL1 might be the most important genetic factors related to cognitive decline in Han Chinese population.

[A rare variant in the sortilin-related receptor 1 gene is associated with declined cognitive functions in the elderly]

AIM

To estimate the association of rs11218343 in the sortilin-related receptor 1 (SORL1) gene with cognitive performance in the elderly and with Alzheimer's disease (AD) in the Russian population.

MATERIAL AND METHODS

A sample included 586 elderly people (mean age 70.9±5.7 years) without AD diagnosis and 100 patients with late-onset AD (mean age 72.1±7.8 years) from the Tomsk population. SORL1 rs11218343 was genotyped using PCR and MALDI-TOF mass spectrometry. Cognitive performance in the sample of elderly without AD was assessed by Montreal Cognitive Assessment (MoCA) test.

RESULTS

Allele frequencies of the SORL1 polymorphism were not significantly different between the elderly without AD and AD patients. However mean MoCA score in the carriers of the rare allele (19.00±6.61) was significantly lower than in homozygotes for the common variant (22.25±3.89) (F=4.97; p=0.026).

CONCLUSION

The rare variant in SORL1 gene previously associated with AD in genome-wide association studies and meta-analyses was associated with lower total МоСА scores in the random sample of elderly people that suggests declined cognitive functions in the carriers of this variant in elderly.

SORL1 gene, plasma biomarkers, and the risk of Alzheimer's disease for the Han Chinese population in Taiwan

Background

The sortilin-related receptor 1 (SORL1) gene, regulating the trafficking and recycling of amyloid precursor protein, has been related to Alzheimer’s disease (AD) and mild cognitive impairment (MCI). The aim of the present study was to investigate the relationship between SORL1 polymorphisms, plasma concentrations of amyloid-beta (Aβ) isoforms, and AD and MCI susceptibility for a Han Chinese population in Taiwan.

Methods

Eight single-nucleotide polymorphisms (SNPs) in SORL1 and the apolipoprotein E gene (APOE) ε4 alleles were genotyped in 798 patients with AD, 157 patients with MCI, and 401 control subjects. Plasma concentrations of Aβ42, Aβ40, and neuropsychiatric tests for six different cognitive domains were examined.

Results

Among the eight tested SNPs, SORL1 rs1784933 was most significantly associated with AD and MCI in our population. The G allele of rs1784933 exerted a protective effect and was associated with a reduced risk of AD (odds ratio [OR] = 0.75, p = 0.004) and MCI (OR = 0.69, p = 0.013). The significance remained after we adjusted for age, sex, and APOE ε4 alleles. For the overall participants, the plasma concentrations of Aβ42 were nominally significant for subjects carrying the rs1784933 G allele having a lower level than those without the G allele (p = 0.046). There was a similar trend for the G allele carriers to have a lower plasma Aβ40 level than noncarriers, but this was not significant. The nonsynonymous SNP rs2298813 was also related to a lower disease risk when AD and MCI were combined as a group (OR = 0.76, p = 0.035). However, there was no association between SORL1 genotypes and any of the six cognitive tests.

Conclusions

Findings from our study provide support for the effect of SORL1 gene on the disease risks and pathognomonic surrogates of AD/MCI. The interaction between SORL1 polymorphisms and Aβ formation requires further study.

SORL1 gene polymorphism association with late-onset Alzheimer's disease

We examined the relationship between loci polymorphisms (rs689021, rs3824966, and rs1784933) of the sortilin-related receptor 1 gene (SORL1) and late-onset Alzheimer's disease (LOAD) in the Chinese Han population of the Hunan Changsha region. A case-control association analysis was used. Clinical data and peripheral blood were collected from 201 Alzheimer's disease patients and 257 healthy controls. PCR and MALDI-TOF mass spectrometry detection technologies were used to identify single nucleotide polymorphism (SNP) distribution at SORL1 gene loci. Genotype and allele frequency differences were analyzed and compared between groups. No significant differences were found in genotype frequency distributions of the rs689021 and rs3824966 loci. Similarly, allele frequency distributions of the C and T alleles of rs689021, and the C and G alleles of rs3824966 showed no significant differences. However, the genotype frequency distribution of the rs1784933 locus was significantly different, and the allele frequency distribution of the A and G alleles were also significantly different. Multifactor logistic regression analysis showed that after correcting for confounding factors such as gender, age, and cholesterol, LOAD risk in rs1784933 AA genotype carriers was 1.803 times that in AG+GG genotype carriers. SORL1 gene SNPs at rs689021 and rs3824966 loci show no relationship with LOAD onset in the Chinese Han population of the Hunan Changsha region. Conversely, a SORL1 gene SNP at the rs1784933 locus is associated with LOAD onset, with the A allele being a risk factor.