Probable novel PSEN2 Val214Leu mutation in Alzheimer's disease supported by structural prediction

Genetic and epigenetic targets of natural dietary compounds as anti-Alzheimer's agents

Alzheimer's disease is a progressive neurodegenerative disorder and the most common cause of dementia that principally affects older adults. Pathogenic factors, such as oxidative stress, an increase in acetylcholinesterase activity, mitochondrial dysfunction, genotoxicity, and neuroinflammation are present in this syndrome, which leads to neurodegeneration. Neurodegenerative pathologies such as Alzheimer's disease are considered late-onset diseases caused by the complex combination of genetic, epigenetic, and environmental factors. There are two main types of Alzheimer's disease, known as familial Alzheimer's disease (onset < 65 years) and late-onset or sporadic Alzheimer's disease (onset ≥ 65 years). Patients with familial Alzheimer's disease inherit the disease due to rare mutations on the amyloid precursor protein (APP), presenilin 1 and 2 (PSEN1 and PSEN2) genes in an autosomal-dominantly fashion with closely 100% penetrance. In contrast, a different picture seems to emerge for sporadic Alzheimer's disease, which exhibits numerous non-Mendelian anomalies suggesting an epigenetic component in its etiology. Importantly, the fundamental pathophysiological mechanisms driving Alzheimer's disease are interfaced with epigenetic dysregulation. However, the dynamic nature of epigenetics seems to open up new avenues and hope in regenerative neurogenesis to improve brain repair in Alzheimer's disease or following injury or stroke in humans. In recent years, there has been an increase in interest in using natural products for the treatment of neurodegenerative illnesses such as Alzheimer's disease. Through epigenetic mechanisms, such as DNA methylation, non-coding RNAs, histone modification, and chromatin conformation regulation, natural compounds appear to exert neuroprotective effects. While we do not purport to cover every in this work, we do attempt to illustrate how various phytochemical compounds regulate the epigenetic effects of a few Alzheimer's disease-related genes.

Orchestration of Genetic Alterations in PSEN1 and PSEN2 Genes in Development of Alzheimer's Disease through Computational Analysis

Dementia is a syndrome that can cause a number of progressive illnesses that affect memory, thinking, and ability to perform everyday tasks. Alzheimer's disease (AD) is the most common cause of dementia and represents a major public health problem. AD is a progressive disease, where in early stages there is mild memory loss and in late-stage patient loses the ability to carry on a conversation. AD (for which there is no exact cause and cure known so far) is the sixth leading cause of deaths in the United States. Every 68 second someone develops AD. This study focuses on protein structure modeling of genes presenilin 1 and 2 ( PSEN1 and PSEN2 ) and their mutated forms (Asn141Tyr found in Chinese family, Gly34Ser identified in a Japanese patient, and Arg62Cys & Val214Leu identified in the Korean patients). It also involves wild and mutant type comparison, protein interaction studies, docking and phylogenetic history based on representative ortholog species and also sheds insight into the comparative evolutionary rates of coding sequence across various orthologs. This study gives a time and cost-effective analysis of genes ( PSEN1 and PSEN2 ) underlying AD and genetic alterations that drive development and causes of disease.

Genetic Screening of Patients with Sporadic Alzheimer's Disease and Frontotemporal Lobar Degeneration in the Chinese Population

Background

Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) account for the vast majority of neurodegenerative dementias. AD and FTLD have different clinical phenotypes with a genetic overlap between them and other dementias.

Objective

This study aimed to identify the genetic spectrum of sporadic AD and FTLD in the Chinese population.

Methods

A total of 74 sporadic AD and 29 sporadic FTLD participants were recruited. All participants underwent whole-exome sequencing (WES) and testing for a hexanucleotide expansion in C9orf72 was additionally performed for participants with negative WES results.

Results

Four known pathogenic or likely pathogenic variants, including PSEN1 (p.G206D), MAPT (p.R5H), LRRK2 (p.W1434*), and CFAP43 (p.C934*), were identified in AD participants, and 1 novel pathogenic variant of ANXA11 (p.D40G) and two known likely pathogenic variants of MAPT (p.D177V) and TARDBP (p.I383V) were identified in FTLD participants. Twenty-four variants of uncertain significance as well as rare variants in risk genes for dementia, such as ABCA7, SORL1, TRPM7, NOS3, MPO, and DCTN1, were also found. Interestingly, several variants in participants with semantic variant primary progressive aphasia were detected. However, no participants with C9orf72 gene variants were found in the FTLD cohort.

Conclusions

There was a high frequency of genetic variants in Chinese participants with sporadic AD and FTLD and a complex genetic overlap between these two types of dementia and other neurodegenerative diseases.

Clinical and genetic characteristics in a central-southern Chinese cohort of early-onset Alzheimer's disease

Background

Mutations in the presenilin-1 (PSEN1), presenilin-2 (PSEN2), and amyloid precursor protein (APP) genes have been commonly identified in early-onset Alzheimer's disease (EOAD). Some of the mutations in the three causative genes, especially the PSEN1 gene, result in variable phenotypes and exhibit clinical heterogeneity among EOAD families.

Methods

Using next-generation sequencing (NGS), we performed genetic screening in a Chinese cohort of 18 patients with EOAD, consisting of five familial EOAD and 13 sporadic cases.

Results

We identified two likely pathogenic PSEN1 mutations (one novel) and a novel APP mutation in three cases of EOAD, where two are familial and one is sporadic, respectively. In addition, we detected a few variants of uncertain significance (VUS) in several genes, including not only the two known variants in PSEN2 (p.H169N and p.V214L) but also genes causal of other types of dementia or previously identified as risk factors for AD, suggesting the possible involvement of multiple genes in the etiopathology of AD. The patients carrying PSEN1 mutations had an earlier mean age at the onset than those with PSEN2 or APP variants. The initial symptoms varied greatly among patients in the EOAD cohort, from progressive memory impairment and epilepsy to uncommon motor symptoms such as involuntary tremors in the upper extremities.

Conclusions

In conclusion, our study provides further evidence of the genetic profile of patients with EOAD from China and expands the mutation spectrum of both PSEN1 and APP. In addition, our results highlight the clinical heterogeneity in patients with EOAD and mutations in PSEN1, PSEN2, and APP and suggest strong effects of genetic variants on clinical phenotypes. Future functional studies are needed to clarify the interaction between AD-causative gene mutations and phenotypic heterogeneity.

PSEN2 and ABCA7 variants causing early-onset preclinical pathological changes in Alzheimer's disease: a case report and literature review

BACKGROUND

Alzheimer's disease (AD) is a debilitating and highly heritable neurodegenerative disease. Early-onset AD (EOAD) was defined as AD occurring before age 65. Although it has a high genetic risk, EOAD due to PSEN2 variation is very rare. ABCA7 is an important risk gene for AD. Previously reported cases mainly carried variations in a single pathogenic or risk gene. METHODS AND RESULTS: In this study, we report a 35-year-old female carrying variants in both the PSEN2 gene (c.640G > T p.V214L) and ABCA7 gene (c.2848G > A p.V950M). Four previously reported cases carried PSEN2 V214L, and no reported cases carried ABCA7 V950M. She had a history of migraine, patent foramen ovale, spontaneous subarachnoid hemorrhage without aneurysm, and multiple cerebral microhemorrhages. Her MMSE score was 24/30, and her MoCA score was 22/30. The concentration of Aβ42 and the ratio of Aβ42 to Aβ40 in cerebral spinal fluid were obviously decreased. Published variants of PSEN2 and ABCA7 in PubMed were reviewed, and the patients' characteristics were summarized and compared to provide information for the clinical diagnosis of AD.

CONCLUSIONS

It is necessary to conduct genetic screening in cases with atypical manifestations.

Genetic study of young-onset dementia using targeted gene panel sequencing in Taiwan

Recent genetic progress allows the molecular diagnosis of young-onset dementia, including Alzheimer's disease (AD) and frontotemporal dementia (FTD). We aimed to identify the mutational and clinical spectra of causal genes in a Taiwanese cohort of young-onset dementia. Ninety-one patients with young-onset dementia and 22 age/gender-matched controls were recruited. Genetic causes were identified by a targeted panel containing 90 causative genes for AD, FTD, and related neurodegenerative disorders. Plasma biomarkers, including total tau, Aβ42, and Aβ40, were assayed. Molecular amyloid and tau PET scans were performed in some patients carrying mutations. Nine of 52 patients (17.3%) with young-onset AD had mutations: 2 (22.2%), 4 (44.5%), 2 (22.2%), and 1 (11.1%) in APP, PSEN1, PSEN2, and TREM2, respectively. Two of 33 patients (6.1%) with young-onset FTD had mutations in MAPT and LRRK2. Three of the 6 patients (50.0%) with possible FTD combined with other neurodegenerative disorders had individual mutations in APP, PSEN2, or MAPT. Patients with PSEN1 mutations had earlier onset of disease than those without mutations (p = .02). Plasma level of total tau was increased and Aβ42 and Aβ40 levels decreased in all groups of dementia patients compared to controls. Our findings provide a genetic spectrum of young-onset dementia in our population.

Molecular Genetics of Early- and Late-Onset Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly and this complex disorder is associated with environmental as well as genetic factors. Early-onset AD (EOAD) and late-onset AD (LOAD, more common) are major identified types of AD. The genetics of EOAD is extensively understood, with three gene variants such as APP, PSEN1, and PSEN2 leading to the disease. Some common alleles, including APOE, are effectively associated with LOAD identified, but the genetics of LOAD is not clear to date. It has been accounted that about 5-10% of EOAD patients can be explained through mutations in the three familiar genes of EOAD. The APOE ε4 allele augmented the severity of EOAD risk in carriers, and the APOE ε4 allele was considered as a hallmark of EOAD. A great number of EOAD patients, who are not genetically explained, indicate that it is not possible to identify disease-triggering genes yet. Although several genes have been identified by using the technology of next-generation sequencing in EOAD families, including SORL1, TYROBP, and NOTCH3. A number of TYROBP variants are identified through exome sequencing in EOAD patients and these TYROBP variants may increase the pathogenesis of EOAD. The existence of the ε4 allele is responsible for increasing the severity of EOAD. However, several ε4 allele carriers propose the presence of other LOAD genetic as well as environmental risk factors that are not identified yet. It is urgent to find out missing genetics of EOAD and LOAD etiology to discover new potential genetic facets which will assist in understanding the pathological mechanism of AD. These investigations should contribute to developing a new therapeutic candidate for alleviating, reversing and preventing AD. This article, based on current knowledge, represents the overview of the susceptible genes of EOAD, and LOAD. Next, we represent the probable molecular mechanism that might elucidate the genetic etiology of AD and highlight the role of massively parallel sequencing technologies for novel gene discoveries.

Exploring the Role of PSEN Mutations in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia. Mutations of presenilin (PSEN) genes that encode presenilin proteins have been found as the vital causal factors for early-onset familial AD (FAD). AD pathological features such as memory loss, synaptic dysfunction, and formation of plaques have been successfully mimicked in the transgenic mouse models that coexpress FAD-related presenilin and amyloid precursor protein (APP) variants. γ-Secretase (GS) is an enzyme that plays roles in catalyzing intramembranous APP proteolysis to release pathogenic amyloid beta (Aβ). It has been found that presenilins can play a role as the GS's catalytic subunit. FAD-related mutations in presenilins can modify the site of GS cleavage in a way that can elevate the production of longer and highly fibrillogenic Aβ. Presenilins can interact with β-catenin to generate presenilin complexes. Aforesaid interactions have also been studied to observe the mutational and physiological activities in the catenin signal transduction pathway. Along with APP, GS can catalyze intramembrane proteolysis of various substrates that play a vital role in synaptic function. PSEN mutations can cause FAD with autosomal dominant inheritance and early onset of the disease. In this article, we have reviewed the current progress in the analysis of PSENs and the correlation of PSEN mutations and AD pathogenesis.

A Review of the Familial Alzheimer's Disease Locus PRESENILIN 2 and Its Relationship to PRESENILIN 1

PRESENILIN 1 (PSEN1) and PRESENILIN 2 (PSEN2) genes are loci for mutations causing familial Alzheimer's disease (fAD). However, the function of these genes and how they contribute to fAD pathogenesis has not been fully determined. This review provides a summary of the overlapping and independent functions of the PRESENILINS with a focus on the lesser studied PSEN2. As a core component of the γ-secretase complex, the PSEN2 protein is involved in many γ-secretase-related physiological activities, including innate immunity, Notch signaling, autophagy, and mitochondrial function. These physiological activities have all been associated with AD progression, indicating that PSEN2 plays a particular role in AD pathogenesis.

Perspectives on ethnic and racial disparities in Alzheimer's disease and related dementias: Update and areas of immediate need

Alzheimer's disease and related dementias (ADRDs) are a global crisis facing the aging population and society as a whole. With the numbers of people with ADRDs predicted to rise dramatically across the world, the scientific community can no longer neglect the need for research focusing on ADRDs among underrepresented ethnoracial diverse groups. The Alzheimer's Association International Society to Advance Alzheimer's Research and Treatment (ISTAART; alz.org/ISTAART) comprises a number of professional interest areas (PIAs), each focusing on a major scientific area associated with ADRDs. We leverage the expertise of the existing international cadre of ISTAART scientists and experts to synthesize a cross-PIA white paper that provides both a concise "state-of-the-science" report of ethnoracial factors across PIA foci and updated recommendations to address immediate needs to advance ADRD science across ethnoracial populations.

Genetic Markers of Alzheimer's Disease

Alzheimer's disease is a complex and heterogeneous, severe neurodegenerative disorder and the predominant form of dementia, characterized by cognitive disturbances, behavioral and psychotic symptoms, progressive cognitive decline, disorientation, behavioral changes, and death. Genetic background of Alzheimer's disease differs between early-onset familial Alzheimer's disease, other cases of early-onset Alzheimer's disease, and late-onset Alzheimer's disease. Rare cases of early-onset familial Alzheimer's diseases are caused by high-penetrant mutations in genes coding for amyloid precursor protein, presenilin 1, and presenilin 2. Late-onset Alzheimer's disease is multifactorial and associated with many different genetic risk loci (>20), with the apolipoprotein E ε4 allele being a major genetic risk factor for late-onset Alzheimer's disease. Genetic and genomic studies offer insight into many additional genetic risk loci involved in the genetically complex nature of late-onset Alzheimer's disease. This review highlights the contributions of individual loci to the pathogenesis of Alzheimer's disease and suggests that their exact contribution is still not clear. Therefore, the use of genetic markers of Alzheimer's disease, for monitoring development, time course, treatment response, and prognosis of Alzheimer's disease, is still far away from the clinical application, because the contribution of genetic variations to the relative risk of developing Alzheimer's disease is limited. In the light of prediction and prevention of Alzheimer's disease, a novel approach could be found in the form of additive genetic risk scores, which combine additive effects of numerous susceptibility loci.

The Whole Exome Sequencing Clarifies the Genotype- Phenotype Correlations in Patients with Early-Onset Dementia

Our study aimed to identify the underlying causes in patients with early onset dementia by clinical and genetic exploration. We recruited a group of 38 patients with early-onset dementia. Firstly, hexanucleotide repeat expansions in C9ORF72 gene were screened in all subjects to exclude the possibility of copy number variation. Then, the whole exome sequencing (WES) was conducted, and the data were analyzed focusing on 89 dementia-related causing and susceptible genes. The effects of identified variants were classified according to the American College of Medical Genetics and Genomics (ACMG) standards and guidelines. There were no pathogenic expansions in C9ORF72 detected. According to the ACMG standards and guidelines, we identified five known pathogenic mutations, PSEN1 P284L, PSEN1c.857-1G>A, PSEN1 I143T, PSEN1 G209E and MAPT G389R, and one novel pathogenic mutation APP K687N. All these mutations caused dementia with the mean onset age of 38.3 (range from 27 to 51) and rapid progression. Eleven variants with uncertain significance were also detected and needed further verification. The clinical phenotypes of dementia are heterogeneous, with both onset ages and clinical features being influenced by mutation position as well as the causative gene. WES can serve as efficient diagnostic tools for different heterogeneous dementia.

A pathogenic PSEN2 p.His169Asn mutation associated with early-onset Alzheimer's disease

Background

Autosomal dominant early-onset Alzheimer’s disease (EOAD) is genetically heterogeneous and has been associated with mutations in 3 different genes, coding for amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2). Most frequent cases are associated with mutations in the PSEN1 gene, whereas mutations in the APP and PSEN2 genes are rare.

Methods

Patient who presented progressive memory decline in her 50s was enrolled in this study. A broad battery of neuropsychological tests and neuroimaging was applied to make the diagnosis. Genetic tests were performed in the patient to evaluate possible mutations using next-generation sequencing (NGS). The pathogenic nature of missense mutation and its 3D protein structure prediction were performed by in silico prediction programs.

Results

A pathogenic mutation in the PSEN2 gene in a Korean patient associated with EOAD was identified. Targeted Next-generation sequencing and Sanger sequencing revealed a heterozygous C to A transition at position 505 (c.505C>A), resulting in a probably missense mutation at codon 169 (p.His169Asn) in PSEN2. PolyPhen-2 and SIFT software analyses predicted this mutation to be a probable damaging variant. This hypothesis was supported by the results of 3D in silico modelling analyses that predicted the p.His169Asn may result in major helix torsion due to histidine to asparagine substitution. Mutation may cause additional stresses with hydrophobic residues on the surface that interact inside the transmembrane domain III, which is a conserved domain in PSEN2 His169.

Conclusion

These findings revealed that the p.His169Asn might be an important residue in PSEN2, which may alter the functions of PSEN2, suggesting its potential involvement with AD phenotype. Future functional studies are needed to evaluate the role of PSEN2 p.His169Asn mutation in AD disease progression.

The genes associated with early-onset Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that accounts for the most cases of dementia, which is characterized by the deposition of dense plaques of amyloid beta (Aβ) plaques and neurofibrillary tangles consisting of hyperphosphorylated tau. The two main types of AD can be classified as early-onset AD (EOAD, onset < 65 years) and late-onset AD (LOAD, onset ≥ 65 years). Evidence from family and twin studies indicate that genetic factors are estimated to play a role in at least 80% of AD cases. The first milestone with linkage analysis revealed the mutations in APP, PSEN1, and PSEN2 genes that cause EOAD. But pathogenic mutations in these three genes can only explain a small fraction of EOAD families. The additional disease-causing genes have not yet been identified. This review provides an overview of the genetic basis of EOAD and the relationship between the functions of these risk genes and the neuropathologic features of AD. A better understanding of genetic mechanisms underlying EOAD pathogenesis and the potentially molecular mechanisms of neurodegeneration will lead to the development of effective diagnosis and treatment strategies for this devastating disease.

Novel Mutation (Gly212Val) in the PS2 Gene Associated with Early-Onset Familial Alzheimer's Disease

Mutations in the presenilin 2 gene (PS2) are an extremely rare cause of early-onset autosomal dominant Alzheimer's disease (AD), accounting for only 5% of these families. These cases represent a particular model of AD, and the scarcity of reports on their clinical phenotypes makes them of great interest. We report a family with early-onset autosomal dominant AD in four members, where the two living siblings were found to carry the novel PS2 mutation Gly212Val (exon 7, transmembrane domain IV) with highly predicted pathogenicity. Age at onset ranged from 60 to 65 years and three of the cases died between ages 74 and 76 years. Clinical phenotype was quite homogeneous among affected members of the family, and overall features, including cognitive decline, tau/p-tau and amyloid-β cerebrospinal fluid markers, neuroimaging, and neuropathology were consistent with typical AD. Lewy bodies were present but restricted to the amygdala.

A case of possibly pathogenic PSEN2 R62C mutation in a patient with probable early-onset Alzheimer's dementia supported by structure prediction

A 49-year-old Korean male patient with dementia was diagnosed with probable early-onset Alzheimer’s disease (AD). He presented with memory problems, personality changes, and disorientation. His family history of dementia was probably negative, since no family member with dementia was found or mentioned. Mild cortical atrophy was observed upon magnetic resonance imaging analyses of his brain, and the single-photon emission computed tomography analysis revealed hypoperfusion in the frontal, temporal, and limbic lobes. The patient was tested for mutations in APP, PSEN1, PSEN2, PGRN, MAPT, and PRNP genes. Genetic analysis revealed R62C mutation in PSEN2 gene. PSEN2 R62C mutation was previously reported in European populations, including Dutch and Belgian families with AD. Herein, we present the first case report of PSEN2 R62C mutation in Asia. PolyPhen-2 and SIFT software analyses predicted this mutation as “possibly damaging”, suggesting its potential involvement with AD. In silico protein structural prediction analyses of PSEN2 R62 and C62 revealed two divergent structures, suggesting that large perturbations of R62C mutation might cause dysfunctions of PSEN2, which may alter the normal amyloid production.

A genetic screen of the mutations in the Korean patients with early-onset Alzheimer's disease

Early-onset Alzheimer's disease (EOAD) has distinct clinical characteristics in comparison to late-onset Alzheimer's disease (LOAD). The genetic contribution is suggested to be more potent in EOAD. However, the frequency of causative mutations in EOAD could be variable depending on studies. Moreover, no mutation screening study has been performed yet employing large population in Korea. Previously, we reported that the rate of family history of dementia in EOAD patients was 18.7% in a nationwide hospital-based cohort study, the Clinical Research Center for Dementia of South Korea (CREDOS) study. This rate is much lower than in other countries and is even comparable to the frequency of LOAD patients in our country. To understand the genetic characteristics of EOAD in Korea, we screened the common Alzheimer's disease (AD) mutations in the consecutive EOAD subjects from the CREDOS study from April 2012 to February 2014. We checked the sequence of APP (exons 16-17), PSEN1 (exons 3-12), and PSEN2 (exons 3-12) genes. We identified different causative or probable pathogenic AD mutations, PSEN1 T116I, PSEN1 L226F, and PSEN2 V214L, employing 24 EOAD subjects with a family history and 80 without a family history of dementia. PSEN1 T116I case demonstrated autosomal dominant trait of inheritance, with at least 11 affected individuals over 2 generations. However, there was no family history of dementia within first-degree relation in PSEN1 L226F and PSEN2 V214L cases. Approximately, 55.7% of the EOAD subjects had APOE ε4 allele, while none of the mutation-carrying subjects had the allele. The frequency of genetic mutation in this study is lower compared to the studies from other countries. The study design that was based on nationwide cohort, which minimizes selection bias, is thought to be one of the contributors to the lower frequency of genetic mutation. However, the possibility of the greater likeliness of earlier onset of sporadic AD in Korea cannot be excluded. We suggest early AD onset and not carrying APOE ε4 allele are more reliable factors for predicting an induced genetic mutation than the presence of the family history in Korean EOAD population.

Mutations, associated with early-onset Alzheimer's disease, discovered in Asian countries

Alzheimer's disease (AD), the most common form of senile dementia, is a genetically complex disorder. In most Asian countries, the population and the number of AD patients are growing rapidly, and the genetics of AD has been extensively studied, except in Japan. However, recent studies have been started to investigate the genes and mutations associated with AD in Korea, the People's Republic of China, and Malaysia. This review describes all of the known mutations in three early-onset AD (EOAD) causative genes (APP, PSEN1, and PSEN2) that were discovered in Asian countries. Most of the EOAD-associated mutations have been detected in PSEN1, and several novel PSEN1 mutations were recently identified in patients from various parts of the world, including Asia. Until 2014, no PSEN2 mutations were found in Asian patients; however, emerging studies from Korea and the People's Republic of China discovered probably pathogenic PSEN2 mutations. Since several novel mutations were discovered in these three genes, we also discuss the predictions on their pathogenic nature. This review briefly summarizes genome-wide association studies of late-onset AD and the genes that might be associated with AD in Asian countries. Standard sequencing is a widely used method, but it has limitations in terms of time, cost, and efficacy. Next-generation sequencing strategies could facilitate genetic analysis and association studies. Genetic testing is important for the accurate diagnosis and for understanding disease-associated pathways and might also improve disease therapy and prevention.

PSEN1 L226F mutation in a patient with early-onset Alzheimer's disease in Korea

In this study, we report a first 226leucine (Leu) mutation to phenylalanine (Phe) in (PSEN1, CTC>TTC, L226F) in Asia from a Korean early-onset Alzheimer's disease (EOAD) patient. Polymerase chain reaction (PCR)-single strand conformation polymorphism, sequencing, and in silico predictions were performed. Previously, L226F was reported in EOAD patients by Zekanowski et al and Gómez-Tortosa et al. Disease phenotypes appeared in their thirties, and family history was positive in both cases. In our patient, age of onset was similar (37 years of age), but the mutation seemed to be de novo, since no affected family member was found. This leucine to phenylalanine substitution may cause additional stresses inside the transmembrane region due to large aromatic side chain and increased hydrophobic interactions with hydrocarbon chains in the membrane and its binding partners. Clinical phenotype of the mutation was aggressive progression into neurodegeneration, resulting in rapid cognitive decline. One of the patients was initially diagnosed with frontotemporal dementia, but the diagnosis was revised to AD upon postmortem studies in which Aβ plaques were seen. A second mutation, L226R, was found for the L226 residue. Similar to L226F, the patient with L226R also developed the first symptoms in his 30s, but EOAD was diagnosed in his 40s. These findings suggested that L226 might be an important residue in PSEN1, since mutations could result in neurodegenerative disease phenotypes at relatively young ages. There are mutations, such as L226F, which may not present clear clinical symptoms for the definitive diagnosis between frontotemporal dementia and AD. In addition, the similarities in the phenotypes could also be possible between AD and frontotemporal dementia, suggesting difficulties in differential diagnosis of various neurodegenerative diseases.

Probable novel PSEN2 Pro123Leu mutation in a Chinese Han family of Alzheimer's disease

We describe a probably novel mutation in exon 5 of the presenilin 2 gene (Pro123Leu) in a Chinese familial early-onset Alzheimer's disease, which clinically manifests as progressive memory loss, cognitive impairment, parkinsonism, and myoclonic jerks. Clinical and neuroimaging examination, target region capture, and high-throughput sequencing were performed in a family of 4 generations. Cerebral perfusion and glucose metabolism were evaluated using arterial spin labeling perfusion magnetic resonance imaging and (18)F-fludeoxyglucose positron emission tomography, respectively. Target region capture sequencing yielded a novel missense mutation at codon 123 (P123L) which is a heterozygous C to T point mutation at position 368 (c.368C>T) in exon 5 of the presenilin 2 leading to a proline-to-leucine substitution. The results were also identified by Sanger sequencing in 7 family members but not in the other 9 unaffected family members and 100 control subjects. This mutation is probably pathogenic and is the first of its kind reported in an early-onset familial AD associated with atypical symptom presentation.

Mutations in presenilin 2 and its implications in Alzheimer's disease and other dementia-associated disorders

Alzheimer's disease (AD) is the most common form of dementia. Mutations in the genes encoding presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein have been identified as the main genetic causes of familial AD. To date, more than 200 mutations have been described worldwide in PSEN1, which is highly homologous with PSEN2, while mutations in PSEN2 have been rarely reported. We performed a systematic review of studies describing the mutations identified in PSEN2. Most PSEN2 mutations were detected in European and in African populations. Only two were found in Korean populations. Interestingly, PSEN2 mutations appeared not only in AD patients but also in patients with other disorders, including frontotemporal dementia, dementia with Lewy bodies, breast cancer, dilated cardiomyopathy, and Parkinson's disease with dementia. Here, we have summarized the PSEN2 mutations and the potential implications of these mutations in dementia-associated disorders.