Molecular Epidemiology of Charcot-Marie-Tooth Disease in Northern Ostrobothnia, Finland: A Population-Based Study.

BACKGROUND: Charcot-Marie-Tooth (CMT) disease is the most common hereditary neuromuscular disorder with a population prevalence of 9.7-82.3/100,000. In this study, we have estimated the prevalence of CMT and its subtypes in Finland and examined the frequency of molecular etiologies. METHODS: A population-based survey included adult patients with peripheral neuropathy from the province of Northern Ostrobothnia, Finland. Secondary causes of peripheral polyneuropathy were excluded and patients with clinical and neurophysiological features pertinent with CMT were included. Molecular diagnostics was carried out when DNA was available. RESULTS: We found 107 subjects with CMT yielding a prevalence 34.6/100,000 in Northern Ostrobothnia. The heterozygous point mutation p.His123Arg in ganglioside induced differentiation associated protein 1 (GDAP1) was found in 31.5% and peripheral myelin protein 22 (PMP22) duplication in 16.9% of the affected. Point mutations in myelin protein zero, mitofusin 2, and gap junction protein beta 1 accounted for 6.7% of the cases. In addition, 18 persons had hereditary neuropathy with liability to pressure palsies and 15 of them carried the PMP22 deletion. CONCLUSIONS: The prevalence of CMT in Northern Ostrobothnia, Finland, seems to be slightly higher than those in previous studies in European populations. Founder mutation in the GDAP1 gene accounts for a large part of the genetically defined CMT2 in Finland.

The effect of TOMM40 poly-T repeat lengths on age of onset and cerebrospinal fluid biomarkers in Finnish Alzheimer's disease patients.

BACKGROUND: Poly-T repeat lengths of rs10524523 in TOMM40 together with APOE polymorphism have been reported to affect the risk of late-onset Alzheimer's disease (LOAD) and the age of onset (AOO). OBJECTIVE: To explore whether the AOO and cerebrospinal fluid biomarkers Aß42, total tau and phosphorylated tau are associated with different repeat lengths. METHODS: We conducted both the fragment and sequencing analysis of rs10524523 in 336 LOAD patients with a known APOE genotype. RESULTS: AOO and Aß42 levels associated significantly with certain poly-T repeat lengths of rs10524523 in LOAD patients encompassing APOE 34/44 genotype. CONCLUSION: We conclude that the poly-T repeat associations of rs10524523 in TOMM40 reflect the APOE ε4-dependent association in LOAD.

Down-regulation of seladin-1 increases BACE1 levels and activity through enhanced GGA3 depletion during apoptosis.

Seladin-1 is a neuroprotective protein selectively down-regulated in brain regions affected in Alzheimer disease (AD). Seladin-1 protects cells against beta-amyloid (Abeta) peptide 42- and oxidative stress-induced apoptosis activated by caspase-3, a key mediator of apoptosis. Here, we have employed RNA interference to assess the molecular effects of seladin-1 down-regulation on the beta-secretase (BACE1) function and beta-amyloid precursor protein (APP) processing in SH-SY5Y human neuroblastoma cells in both normal and apoptotic conditions. Our results show that approximately 60% reduction in seladin-1 protein levels, resembling the decrease observed in AD brain, did not significantly affect APP processing or Abeta secretion in normal growth conditions. However, under apoptosis, seladin-1 small interfering RNA (siRNA)-transfected cells showed increased caspase-3 activity on average by 2-fold when compared with control siRNA-transfected cells. Increased caspase-3 activity coincided with a significant depletion of the BACE1-sorting protein, GGA3 (Golgi-localized gamma-ear-containing ADP-ribosylation factor-binding protein), and subsequently augmented BACE1 protein levels and activity. Augmented BACE1 activity in turn correlated with the enhanced beta-amyloidogenic processing of APP and ultimately increased Abeta production. These adverse changes associated with decreased cell viability in seladin-1 siRNA-transfected cells under apoptosis. No changes in GGA3 or BACE1 levels were found after seladin-1 knockdown in normal growth conditions. Collectively, our results suggest that under stress conditions, reduced seladin-1 expression results in enhanced GGA3 depletion, which further leads to augmented post-translational stabilization of BACE1 and increased beta-amyloidogenic processing of APP. These mechanistic findings related to seladin-1 down-regulation are important in the context of AD as the oxidative stress-induced apoptosis plays a key role in the disease pathogenesis.

Alzheimer's Disease-Related Polymorphisms in Shunt-Responsive Idiopathic Normal Pressure Hydrocephalus.

BACKGROUND: Idiopathic normal pressure hydrocephalus (iNPH) is a late onset, surgically treated progressive brain disease caused by impaired cerebrospinal fluid dynamics and subsequent ventriculomegaly. Comorbid Alzheimer's disease (AD) seems to be frequent in iNPH. OBJECTIVE: We aim to evaluate the role of AD-related polymorphisms in iNPH. METHODS: Overall 188 shunt-operated iNPH patients and 688 controls without diagnosed neurodegenerative disease were included into analysis. Twenty-three single-nucleotide polymorphisms (SNPs FRMD4A [rs7081208_A, rs2446581_A, rs17314229_T], CR1, BIN, CD2AP, CLU, MS4A6A, MS4A4E, PICALM, ABCA7, CD33, INPP5D, HLA_DRB5, EPHA1, PTK2B, CELF1, SORL1, FERMT2, SLC24A, DSG2, CASS4, and NME8) adjusted to APOE were analyzed between groups by using binary logistic regression analysis. Neuroradiological characteristics and AD-related changes in the right frontal cortical brain biopsies were available for further analysis. RESULTS: Logistic regression analysis adjusted to age, gender, and other SNPs indicated allelic variation of NME8 between iNPH patients and non-demented controls (p = 0.014). The allelic variation of NME8 was not related to the neuropathological changes in the brain biopsies of iNPH patients. However, periventricular white matter changes (p = 0.017) were more frequent in the iNPH patients with the AA-genotype, an identified risk factor of AD. CONCLUSIONS: Our findings increase the evidence that iNPH is characterized by genetic and pathophysiological mechanisms independent from AD. Considering that NME8 plays a role in the ciliary function and displays SNP-related diversity in white matter changes, the mechanisms of NME8 in iNPH and other neurodegenerative processes are worth further study.

Effects of Alzheimer's Disease-Associated Risk Loci on Amyloid-ß Accumulation in the Brain of Idiopathic Normal Pressure Hydrocephalus Patients.

BACKGROUND: Idiopathic normal pressure hydrocephalus (iNPH) is a dementing condition featuring characteristic symptoms, ventriculomegaly, and normal or slightly elevated cerebrospinal fluid pressure. In Alzheimer's disease (AD) patients, diffuse aggregates of amyloid-ß (Aß) and neurofibrillary hyperphosphorylated tau are detected in the neocortex of the brain, while similar accumulation of Aß is also detected in iNPH. Recent genome-wide association studies have identified several novel risk loci for AD, potentially affecting Aß-related cellular processes. Apart from the apolipoprotein E ɛ4 allele (APOE4), the risk effect of single loci is low, emphasizing the importance of the polygenic risk score approach when assessing the combined effects. OBJECTIVE: To study the effects of AD-associated individual and polygenic risk score of single nucleotide polymorphisms (SNPs) on the accumulation of Aß in the brain samples of iNPH patients. METHODS: A sample set of frontal cortex biopsies from 188 iNPH patients were divided into two groups according to the Aß pathology. After the genotyping of the AD-associated risk loci, polygenic risk score was calculated for each iNPH patient and subsequently analyzed in relation to Aß deposition. RESULTS: Apart from the APOE4, none of the SNPs revealed a statistically significant effect on the accumulation of Aß in iNPH. Also, the non-APOE4 polygenic risk score did not associate with Aß deposition. CONCLUSION: Novel AD-associated risk genes have no significant effect on Aß accumulation in the brain of iNPH patients. However, APOE4 affects the Aß deposition in the brain of iNPH and AD patients in a similar manner.

The role of the FTD-ALS associated C9orf72 expansion in suicide victims.

Impulsive and aggressive traits are not only common features displayed by patients with behavioural variant frontotemporal dementia (bvFTD), they may well be the first clinical manifestations of the disease. In addition, suicidal behaviour has been postulated to be a symptom of bvFTD. A hexanucleotide repeat expansion in chromosome 9 open reading frame 72 (C9orf72) is the major genetic cause for familial bvFTD. During recent years, several genetic factors predisposing to suicide have been identified, but there are no previous studies analysing the role of the C9orf72 expansion in suicides. In the present study, we aimed to analyse the prevalence of the C9orf72 expansion in unselected suicide victims. The prevalence of the C9orf72 expansion was analysed in a cohort of 109 Finnish victims of suicide (mean age at death 46.1 years; range 18-86 years). The C9orf72 expansion was analysed from the post mortem blood samples. Results showed that no abnormal length C9orf72 expansions were detected in the study cohort. In conclusion, even though suicidal behaviour may be encountered in bvFTD patients, the C9orf72 expansion is not a common genetic finding in unselected suicide victims.

The C9ORF72 expansion sizes in patients with psychosis: a population-based study on the Northern Finland Birth Cohort 1966.

Patients with behavioral variant frontotemporal dementia (bvFTD) have many psychotic symptoms, especially at the onset of the disease. The C9ORF72 expansion is the most common genetic etiology observed with bvFTD and the prevalence of the expansion is notably high among Finnish bvFTD patients. The aim of this study was to evaluate the prevalence of the C9ORF72 expansion among the clearly characterized patients with psychosis, mainly schizophrenia, in early midlife. The C9ORF72 repeat sizes were analyzed in 130 (48% women) patients with psychosis from the Northern Finland Birth Cohort 1966 (N=11,017), the mean onset age being 27.9 (SD 7.0) years. Despite the high frequency of psychiatric symptoms in bvFTD patients and the extremely high prevalence of the C9ORF72 expansion in Finland, pathogenic expansion (>40 repeats) was not detected among the Northern Finland Birth Cohort 1966 individuals with psychosis, indicating that these disorders, especially schizophrenia before the age of 43 years, may not be associated with the C9ORF72 expansion. However, we identified four cases with intermediate size repeats (17-26), but the role of the intermediate repeats in the etiology of psychosis is unknown.

Genetic Variation in δ-Opioid Receptor Associates with Increased ß- and γ-Secretase Activity in the Late Stages of Alzheimer's Disease.

The agonist-induced activation of human δ-opioid receptor (δOR) has been shown to increase ß- (BACE1) and γ-secretase activities leading to increased production of amyloid-ß (Aß) peptide. We have recently shown that phenylalanine to cysteine substitution at amino acid 27 in δOR (δOR-Phe27Cys) increases amyloid-ß protein precursor processing through altered endocytic trafficking. Also, a genetic meta-analysis of the δOR-Phe27Cys variation (rs1042114) in two independent Alzheimer's disease (AD) patient cohorts indicated that the heterozygosity of δOR-Phe27Cys increases the risk of AD. Here, we investigated α-, ß-, and γ-secretase activities in human brain with respect to δOR-Phe27Cys variation in the temporal cortex of 71 subjects with varying degree of AD-related neurofibrillary pathology (Braak stages I-VI). As a result, a significant increase in ß- (p = 0.03) and γ- (p = 0.01), but not α-secretase, activities was observed in late stage AD samples (Braak stages V-VI), which were heterozygous for δOR-Phe27Cys as compared to the δOR-Phe27 and δOR-Cys27 homozygotes. The augmented ß-secretase activity was not associated with increased mRNA expression or protein levels of BACE1 in the late stage AD patients, who were heterozygous for the δOR-Phe27Cys variation. These findings suggest that δOR-Phe27Cys variation modulates ß- and γ-secretase activity in the late stages of AD likely via post-translational mechanisms other than alterations in the mRNA or protein levels of BACE1, or, in the expression of γ-secretase complex components.

Effects of Alzheimer's disease-associated risk loci on cerebrospinal fluid biomarkers and disease progression: a polygenic risk score approach.

BACKGROUND: Several risk loci for Alzheimer's disease (AD) have been identified during recent years in large-scale genome-wide association studies. However, little is known about the mechanisms by which these loci influence AD pathogenesis. OBJECTIVE: To investigate the individual and combined risk effects of the newly identified AD loci. METHODS: Association of 12 AD risk loci with AD and AD-related cerebrospinal fluid (CSF) biomarkers was assessed. Furthermore, a polygenic risk score combining the effect sizes of the top 22 risk loci in AD was calculated for each individual among the clinical and neuropathological cohorts. Effects of individual risk loci and polygenic risk scores were assessed in relation to CSF biomarker levels as well as neurofibrillary pathology and different biochemical measures related to AD pathogenesis obtained from the temporal cortex. RESULTS: Polygenic risk scores associated with CSF amyloid-ß42 (Aß42) levels in the clinical cohort, and with soluble Aß42 levels and γ-secretase activity in the neuropathological cohort. The γ-secretase effect was independent of APOE. APOE-ε4 associated with CSF Aß42 (p < 0.001) levels. For the other risk loci, no significant associations with AD risk or CSF biomarkers were detected after multiple testing correction. CONCLUSIONS: AD risk loci polygenically contribute to Aß pathology in the CSF and temporal cortex, and this effect is potentially associated with increased γ-secretase activity.

Effects of NR1H3 genetic variation on the expression of liver X receptor α and the progression of Alzheimer's disease.

Alzheimer's disease (AD) has been postulated to involve defects in the clearance of amyloid-ß (Aß). Activation of liver X receptor α (LXRα) increases the expression of apolipoprotein E (ApoE) as well as cholesterol transporters ABCA1 and ABCG1, leading to augmented clearance of Aß. We have previously shown that the C allele of rs7120118 in the NR1H3 gene encoding LXRα reduces the risk of AD. Here, we wanted to assess whether the rs7120118 variation affects the progression of AD and modulates the expression of NR1H3 and its downstream targets APOE, ABCA1 and ABCG1.We utilized tissue samples from the inferior temporal cortex of 87 subjects, which were subdivided according to Braak staging into mild, moderate and severe AD groups on the basis of AD-related neurofibrillary pathology. APOE ε4 allele increased soluble Aß42 levels in the tissue samples in a dose-dependent manner, but did not affect the expression status of APOE. In contrast, the CC genotype of rs7120118 was underrepresented in the severe group, although this result did not reach statistical significance. Also, patients with the CC genotype of rs7120118 showed significantly decreased soluble Aß42 levels as compared to the patients with TT genotype. Although the severity of AD did not affect NR1H3 expression, the mRNA levels of NR1H3 among the patients with CT genotype of rs7120118 were significantly increased as compared to the patients with TT genotype. These results suggest that genetic variation in NR1H3 modulates the expression of LXRα and the levels of soluble Aß42.

Genetic loci associated with Alzheimer's disease and cerebrospinal fluid biomarkers in a Finnish case-control cohort.

OBJECTIVES: To understand the relation between risk genes for Alzheimer's disease (AD) and their influence on biomarkers for AD, we examined the association of AD in the Finnish cohort with single nucleotide polymorphisms (SNPs) from top AlzGene loci, genome-wide association studies (GWAS), and candidate gene studies; and tested the correlation between these SNPs and AD markers Aß(1-42), total tau (t-tau), and phosphorylated tau (p-tau) in cerebrospinal fluid (CSF). METHODS: We tested 25 SNPs for genetic association with clinical AD in our cohort comprised of 890 AD patients and 701-age matched healthy controls using logistic regression. For the correlational study with biomarkers, we tested 36 SNPs in a subset of 222 AD patients with available CSF using mixed models. Statistical analyses were adjusted for age, gender and APOE status. False discovery rate for multiple testing was applied. All participants were from academic hospital and research institutions in Finland. RESULTS: APOE-ε4, CLU rs11136000, and MS4A4A rs2304933 correlated with significantly decreased Aß(1-42) (corrected p<0.05). At an uncorrected p<0.05, PPP3R1 rs1868402 and MAPT rs2435211 were related with increased t-tau; while SORL1 rs73595277 and MAPT rs16940758, with increased p-tau. Only TOMM40 rs2075650 showed association with clinical AD after adjusting for APOE-ε4 (p = 0.007), but not after multiple test correction (p>0.05). CONCLUSIONS: We provide evidence that APOE-ε4, CLU and MS4A4A, which have been identified in GWAS to be associated with AD, also significantly reduced CSF Aß1-42 in AD. None of the other AlzGene and GWAS loci showed significant effects on CSF tau. The effects of other SNPs on CSF biomarkers and clinical AD diagnosis did not reach statistical significance. Our findings suggest that APOE-ε4, CLU and MS4A4A influence both AD risk and CSF Aß1-42.